Patent Publication Number: US-10788678-B2

Title: High brightness solid state illumination system for fluorescence imaging and analysis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 15/924,943, entitled High Brightness Solid State Illumination System for Fluorescence Imaging and Analysis, which was filed on Mar. 19, 2018, which was a continuation of then co-pending U.S. patent application Ser. No. 14/862,492, entitled High Brightness Solid State Illumination System for Fluorescence Imaging and Analysis, which was filed on Sep. 23, 2015, said application is a continuation-in-part (CIP) of U.S. patent application Ser. No. 13/897,237, entitled High Brightness Solid States Illumination System for Fluorescence Imaging and Analysis, which was filed on May 17, 2013, which was related to co-pending U.S. patent application Ser. No. 13/900,089, filed May 22, 2013, entitled “High Brightness Illumination System and Wavelength Conversion Module for Microscopy and Other Applications”, which claims priority from U.S. Provisional patent application Ser. No. 61/651,130, filed May 24, 2012. Each of these prior applications is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to high brightness solid state illumination systems, particularly illumination systems for fluorescence imaging and analysis. 
     BACKGROUND 
     High radiance illumination sources are required for fluorescence imaging and analysis, including fluorescence microscopy. Some applications require broadband or white light illumination. Other applications require relatively narrow band illumination of a particular wavelength range in the ultraviolet (UV), visible or infrared (IR) spectral region. 
     For example, conventional microscopy illumination systems typically utilize short arc lamps such as high pressure mercury, metal halide, and xenon lamps. These lamps are capable of very high radiance and are suitable sources for direct coupled illumination systems, as well as light guide coupled illumination systems, e.g. using a liquid light guide or a fiber light guide. Nevertheless, it is recognized that there are a number of problems associated with conventional lamp technologies, such as short lifetime, temporal variation of the output power, high voltage operation (typically kilovolts are required to strike the lamp), and use of mercury. The latter is now seen as an environmental hazard and subject to regulations to limit use in numerous countries throughout the world. 
     Solid state light lighting technology has progressed significantly in recent years and some high brightness light sources using solid state Light Emitting Devices (LEDs), e.g. light emitting diodes, are now available that can potentially provide sufficiently high radiance, broadband illumination for replacement of conventional arc lamps. Solid state LED light sources can offer advantages over conventional arc lamps, such as, much improved lifetime, lower cost of ownership, lower voltage operation, lower power consumption (enabling some battery operated portable devices), and freedom from mercury. Additionally LED light sources can be readily controlled electronically, by modulating the current or voltage driving the device, which allows for fast switching and intensity control through the LED driver, which can be a significant advantage in many applications. 
     Nevertheless, despite technological advances in LED technology, high brightness LED light sources are not available to cover all wavelengths required for illumination systems for fluorescence imaging and analysis. In particular, the output of LED devices still do not match the radiance of traditional arc-lamps in some regions of the visible spectrum, especially in the 540 nm to 630 nm spectral band, i.e. in the green/yellow/amber range of the visible spectrum. The solid state lighting industry refers to this issue as the “green gap”. Emission in this region of the spectrum is fundamentally limited by the lack of availability of semiconductor materials having a suitable band gap to produce light of the required wavelength. 
     This is a particular problem for fluorescence imaging and analysis which may, for example, require illumination of a biological sample with a relatively narrow band of illumination of a particular wavelength that is absorbed by a selected fluorophore or marker in the substance under test. 
     For example, a traditional fluorescence illumination system, e.g. for fluorescence imaging or microscopy, comprises a short arc mercury lamp which provides light emission having spectral peaks near 365 nm, 405 nm, 440 nm, 545 nm and 575 nm. Standard fluorophores that are commonly used for fluorescence imaging and analysis are selected to have absorption spectra having peaks optimized to match these lamp emission peaks. To replace a standard mercury lamp illuminator with a LED based illuminator, it is desirable to be able to provide emission at the same wavelengths and with a comparable output power. There are suitably powerful LEDs that are commercially available for emission at 365 nm, 405 nm, 440 nm. However, in view of the “green gap” mentioned above, there are currently no single color, high brightness LEDs commercially available for emission at 545 nm and 575 nm. 
     It is well known in the art of LED lighting and illumination to use LEDs in combination with luminescent materials, i.e. fluorescent materials or phosphors, to generate light of wavelengths that are outside the range emitted directly by the LEDS, i.e. by wavelength conversion. In particular, a UV or blue light emitting LED may be combined with a remote or direct die-contact phosphor layer or coating to obtain broadband light emission of a desired color temperature. For example, a blue light emitting diode or diode array with an emission peak in the range between 445 nm and 475 nm is combined with a phosphor layer comprising particles of Ce:YAG (cerium doped yttrium aluminum garnet) suspended in an encapsulant material such as silicone, which is deposited directly on the LED. The blue light from the LED is absorbed by the phosphor and generates a broadband green/yellow/amber light which combines with the scattered blue light to produce a spectrum that provides the perception of white light. The overall brightness is limited by the blue light intensity from the LED and thermal quenching of the phosphor, and the spectrum provides limited emission in regions of the spectrum seen as green/yellow, approximately 560 nm and amber, approximately 590 nm. 
     Thus, relative to a mercury lamp, commercially available white light LEDs that use a blue light emitting LED combined with a Ce:YAG phosphor, produce significantly weaker emission in the 545 nm and 575 nm regions. For example, at the objective plane of a microscope, output power at 545 nm and 575 nm from such a white light LED was found to be about 10 times lower than the output power from a mercury lamp. This level of power is insufficient for most conventional fluorescence microscopy applications. 
     By increasing the drive current, some improvement of the light output can be achieved, but fundamentally, the power in this circumstance is limited by the maximum drive current density (i.e. current per unit area) and factors, such as, the LED optical to electrical conversion efficiency, the LED output intensity, the phosphor quantum efficiency, and thermal quenching of both the LED and phosphor, as well as the cooling capacity. Even in the best case, the output from an overdriven air cooled white LED is still 4 to 5 times less than a conventional lamp within the 545 nm and 575 nm spectral range and the lifetime may be significantly reduced by overdriving the device. 
     The following references provide some other examples of the use of LED sources combined with fluorescent materials or phosphors in other forms. 
     U.S. Pat. No. 7,898,665 to Brukilacchio et al., issued Mar. 1, 2011, entitled “Light Emitting Diode Illumination System,” for example, discloses a system comprising an arrangement of multiple LEDS that are coupled to a fluorescent rod which emits at a different wavelength to provide sufficiently high brightness illumination for applications such as microscopy or endoscopy. For example a single crystal of Ce:YAG may be pumped by multiple LEDs to generate yellow or amber emission. However, the efficiency of such a device would be limited by total internal reflection due to the high index of refraction of Ce:YAG and requires coupling of multiple LEDs to generate output of sufficient brightness, which increases the cost, size, thermal and electrical requirements. 
     To provide a more compact and efficient system, the above referenced related U.S. Patent application No. 61/651,130, discloses an illumination system that comprises a laser light source, e.g. providing blue light emission in the 440 nm to 490 nm range, for excitation of a wavelength conversion module comprising a wavelength conversion medium, such as Ce:YAG crystal, of a particular shape and size, set in a mounting for thermal dissipation, and an optical concentrator. The shape and size of the wavelength conversion crystal, provides a compact light source with a configuration suitable for applications that require high brightness and narrow bandwidth illumination at a selected wavelength, e.g. for fluorescence microscopy, or other applications requiring étendue-limited coupling or light guide coupling. While effective, due to the particular shape and size of the crystal and cooling requirements, this system is currently relatively costly to manufacture. A solution that is lower cost, compact and provides a broader spectrum is desirable for some applications. 
     Thus, there is a need for improved or alternative high radiance illumination sources, particularly those that can provide illumination at wavelengths of 545 nm and 575 nm, for example, for fluorescence imaging and analysis applications. 
     SUMMARY OF THE INVENTION 
     The present invention seeks to overcome or mitigate one or more disadvantages of known high brightness illumination systems for fluorescence imaging and analysis, or at least provide an alternative. 
     Thus, one aspect of the present invention provides a method of providing high brightness illumination for fluorescence imaging and analysis, comprising: providing a first light source comprising a light emitting device (LED) and a phosphor layer, the LED emitting a first wavelength λ 1  within an absorption band of the phosphor layer and the phosphor layer emitting broadband light emission of longer wavelength comprising light in a wavelength band Δλ PHOSPHOR ; providing a second light source comprising a laser emitting a second wavelength λ 2 , within the absorption band of the phosphor layer; and while operating the LED to generate emission at λ 1  and Δλ PHOSPHOR , concurrently optically pumping the phosphor layer with laser emission λ 2  to increase emission intensity in the phosphor emission wavelength band Δλ PHOSPHOR . In some implementations, the phosphor layer is optically pumped by the LED or the laser, but not concurrently by both. 
     The method may comprise optically coupling emission comprising λ1 and Δλ PHOSPHOR , along a common optical axis, to an optical output. The method may comprise providing another light source emitting another wavelength λ 3 , and optically coupling emission comprising λ 1 , Δλ PHOSPHOR  and λ 3 , along a common optical axis, to an optical output. 
     By way of example, the LED light source may comprise a standard white light emitting LED light source, i.e. comprising a blue light emitting LED emitting at wavelength λ 1  and a yellow Ce:YAG phosphor layer or coating providing broadband emission over a wavelength band Δλ PHOSPHOR . Typically, during normal operation of the blue light emitting LED, the phosphor layer is not saturated by light from the blue LED. Thus, concurrent optical pumping of the phosphor layer with the laser wavelength λ 2 , within the absorption band of the Ce:YAG phosphor layer, effectively increases the phosphor emission Δλ PHOSPHOR  in the green, yellow and amber regions of the spectrum. 
     In particular, the supplementary laser optical pumping of the phosphor provides increased optical output over the emission band of the phosphor, so that sufficiently high radiance can be achieved at specific wavelengths, e.g. 545 nm and 575 nm, which are conventionally used for fluorescence imaging and analysis applications. 
     Another aspect of the present invention provides an illumination system for fluorescence imaging and analysis, comprising: a light source module comprising: a first light source comprising a first light emitting device (LED) and a phosphor layer, the first LED for providing emission at a first wavelength λ 1  within an absorption band of the phosphor layer and the phosphor layer providing broadband light emission of longer wavelength comprising light in a wavelength band Δλ PHOSPHOR ; a second light source for providing laser emission at a second wavelength λ 2 , within the absorption band of the phosphor layer; a controller for driving the first light source to generate emission at λ 1  and Δλ PHOSPHOR  and for concurrently driving the laser and optically pumping the phosphor layer with the laser wavelength λ 2 , to increase emission in the emission band of the phosphor Δλ PHOSPHOR ; and optical coupling means for coupling light emission to an optical output of the illumination system. 
     Thus a laser pumped LED light source unit or module is provided, which has a high radiance output in the emission band of the phosphor Δλ PHOSPHOR . The pump laser wavelength λ 2  may be the same as the LED wavelength λ 1 , or different from λ 1 , provided it is within the absorption band of the phosphor layer. The laser is preferably a solid state laser, e.g. a laser diode, and the control unit provides LED/laser controllers and LED/laser drivers. A suitable choice of phosphor allows for an optical output with high brightness at particular wavelengths, e.g. for applications such as fluorescence imaging and analysis. The phosphor layer may be selected to cover a band within the spectral range from 350 nm to 750 nm and more particularly from 530 nm to 630 nm, i.e. within in the green gap. 
     In particular, this system provides for high brightness (i.e. high radiance) illumination, e.g., in the 545 nm and 575 nm bands, which are commonly used for fluorescence imaging and analysis, such as, for fluorescence microscopy and for array slide scanners. 
     The optical coupling means comprises one or more optical elements such as lenses or optical concentrators for focusing the laser emission onto the phosphor layer, collecting emission at λ 1  and Δλ PHOSPHOR , and coupling the emission at these wavelengths to the optical output of the light source module. 
     For example, the optical coupling means comprises an optical element for coupling the laser wavelength λ 2  to the phosphor layer for optical pumping of the phosphor layer and for coupling emission from the first LED and the phosphor layer, comprising λ 1  and Δλ PHOSPHOR , to the optical output. Preferably the optical element comprises a dichroic element that acts as a beam-splitter/combiner for coupling the laser wavelength λ 2  onto the phosphor layer for optical pumping of the phosphor layer and for coupling emission from the first LED and the phosphor layer, comprising λ 1  and Δλ PHOSPHOR , to the optical output. 
     If the pump laser wavelength λ 2  is less than the wavelength emission λ 1  of the LED, in a preferred embodiment, the dichroic element has a band edge λ D  greater than the laser wavelength λ 2 , so that it reflects the laser emission λ 2  and transmits output light emission comprising λ 1  and Δλ PHOSPHOR . 
     As an example, λ 1  comprises emission in the range from 445 nm to 475 nm, i.e. from a blue LED, and Δλ PHOSPHOR  covers the emission wavelength range from 500 nm to 750 nm. Preferably Δλ PHOSPHOR  covers the emission wavelength range from at least 530 to 630 nm (i.e. the “green gap”), and the pump laser wavelength λ 2  is 450 nm or less. 
     A dichroic beam-splitter/combiner, having a band edge wavelength λ D , between λ 1  and λ 2 , may be positioned for reflecting the laser emission λ 2  and transmitting output light emission comprising λ 1  and Δλ PHOSPHOR . For example, for wavelength ranges in the example above, if the pump laser wavelength λ 2  is 440 nm, and the blue LED emits λ 1  in the range from 445 nm to 475 nm, the dichroic element has a band edge λ D  of 443 nm. 
     The illumination system may further comprise one or more additional light sources, e.g. at least one of a LED light source providing an emission wavelength λ 3  and an LED light source providing emission at wavelength λ 4 . For example, these additional LED light sources are individual LED light sources that provide outputs λ 3  and λ 4  in the near UV and UV spectral regions, respectively. Optical coupling elements are provided to couple outputs at these and other wavelengths, along a common optical axis, to the optical output of the system. 
     Optical coupling elements may include a second dichroic element, i.e. a dichroic beam-splitter/combiner, for combining outputs λ 3  and λ 4 , and then the first dichroic element combines λ 3  and λ 4  with λ 1  and Δλ PHOSPHOR . For example, the first LED has an emission band λ 1  in the range between 440 nm and 490 nm and more preferably between 445 nm and 475 nm. The Δλ PHOSPHOR  band emitted by the phosphor layer is in the range from 500 nm to 750 nm and more preferably in the range from 530 nm to 630 nm. If the phosphor layer is Ce:YAG as described above, the laser wavelength λ 1  is preferably 450 nm or less, for optical pumping of the phosphor layer. The additional individual LED light sources provide λ 3  comprising near UV emission in the range from 410 nm to 445 nm and λ 4  comprising UV emission in the range from 370 nm to 410 nm or from 350 nm to 390 nm. 
     In this example, a second dichroic element having a band pass edge wavelength between λ 3  and λ 4 , e.g. 409 nm, is used to combine these two wavelengths. Then, if the laser pump wavelength λ 2 , and LED emission at λ 3  and λ 4 , are all on the short wavelength side of the 443 nm band edge wavelength λ D  of the first dichroic element, this element combines λ 3  and λ 4  with λ 1  and Δλ PHOSPHOR , along the primary optical axis, to provide an optical output comprising each of these wavelengths. 
     Optionally the system may comprise one or more additional individual LED light sources and/or one or more additional light source modules for light emission in other spectral bands. For example, additional light sources may provide spectral bands that are in the ultraviolet and near ultraviolet region. These additional sources may comprise, e.g.: a UV LED emitting in the range from 350 nm to 390 nm, e.g. having a peak at 365 nm; or a UV LED emitting in the range from 370 to 410 nm, e.g. having a peak at 385 nm; or a phosphor coated UV LED emitting in the near UV range from 410 nm to 445 nm. 
     In one embodiment, the at least one additional light source or light source module comprises a LED providing emission at λ 4  and a phosphor layer (Phosphor2) providing a broad emission band Δλ PHOSPHOR2 . For example, if both λ 4  and Δλ PHOSPHOR2  lie on the same side (i.e. the short wavelength side in the example above) of the band edge wavelength λ D  of the first dichroic element, the dichroic element combines λ 4  and Δλ PHOSPHOR2  with λ 1  and Δλ PHOSPHOR , to enable coupling of each of these wavelength bands, along the primary optical axis, to the optical output of the light source unit. 
     Typically, an optical filtering system within a fluorescence imaging system, such as a fluorescence microscope, provides for further filtering of a selected wavelength band from the output of the illumination system. 
     If desired, the illumination system may also comprise one or more additional LED light source modules, providing other wavelength bands. It may comprise an additional laser pumped LED light source module, i.e. a second pump laser emitting a wavelength λ 5  within an absorption band of a second phosphor layer (Phosphor2), for optically pumping the second phosphor layer (Phosphor2). A second dichroic beam-splitter/combiner may be provided, having a wavelength edge that is selected to reflect the laser wavelength λ 5  and transmit the emission bands at λ 4  and Δλ PHOSPHOR2 . 
     Another aspect of the present invention provides illumination system for fluorescence imaging and analysis, comprising: first and second light source modules and a controller; 
     the first light source module for providing emission in a first wavelength band, comprising: a first light source comprising a first LED and a first phosphor layer, the first LED providing emission at a first wavelength λ 1  within an absorption band of the phosphor layer and the first phosphor layer providing broadband light emission Δλ PHOSPHOR1 ; a second light source comprising a laser emitting at a second wavelength λ 2 , within the absorption band of the first phosphor layer; wherein the controller concurrently drives the first light source to generate emission comprising λ 1  and Δλ PHOSPHOR1  and drives the laser for optically pumping the first phosphor layer with the laser wavelength λ 2  to increase emission in the emission band of the phosphor Δλ PHOSPHOR1 ; 
     the second module for providing emission in a second wavelength band different from the first wavelength band, comprising: a third light source comprising second LED and a second phosphor layer different from the first phosphor layer, the second LED emitting at a wavelength λ 4  within an absorption band of the second phosphor layer and the second phosphor layer providing broadband light emission Δλ PHOSPHOR2 ; a fourth light source comprising a laser emitting at a wavelength λ 5  within the absorption band of the second phosphor layer; wherein the controller concurrently drives the second light source to generate emission comprising λ 4  and Δλ PHOSPHOR2  and the laser for optically pumping the second phosphor layer with the laser wavelength λ 5  and the laser wavelength λ 5 , to increase emission in the emission band of the second phosphor Δλ PHOSPHOR2 ; and 
     optical coupling means comprising at least one dichroic beam-splitter/combiner for coupling one or more of λ 1 , Δλ PHOSPHOR1 , λ 4  and Δλ PHOSPHOR2 , along a common optical axis, to an optical output of the illumination system. 
     The optical coupling means comprises optical coupling elements such as a coupling lens, an optical concentrator or other optics, and one or more dichroic elements having suitable passband, i.e. dichroic beam-splitters/combiners, to enable the LED light sources and laser light sources to be compactly arranged and for optically coupling the light emission from the LEDs and the phosphor layers to the primary optical axis, aligned to the optical output of the illumination system. The optical coupling elements may comprise dichroic elements for splitting and/or combining emission wavelengths from each light source, as required, and preferably first and second dichroic beam-splitters/combiners having band edges selected for reflecting laser wavelengths λ 2  and λ 5 , respectively. 
     An illumination system, according to preferred embodiments of the invention, has the potential of meeting and exceeding the output of the best arc lamps systems available today at particular wavelengths used for fluorescence microscopy, while overcoming at least some of the limitations of existing high brightness LED light sources. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, of preferred embodiments of the invention, which description is by way of example only. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the drawings, identical or corresponding elements in the different Figures have the same reference numeral, or corresponding elements have reference numerals incremented by 100 in successive Figures. 
         FIG. 1  illustrates schematically an illumination system comprising a light source module according to a first embodiment of the invention; 
         FIG. 2  illustrates schematically an illumination system comprising a light source module according to a second embodiment; 
         FIG. 3  shows spectral data for the light source module  100 - 1  illustrated in  FIG. 2 , without laser pumping and with laser pumping; 
         FIG. 4  shows experimental results comparing the optical output power of the light source module illustrated in  FIG. 2 , with and without laser pumping; 
         FIG. 5  illustrates schematically an illumination system according to a third embodiment, wherein a light source unit comprises a first light source module similar to that shown in  FIG. 2 , together with two additional LED light sources; 
         FIG. 6  illustrates schematically an illumination system according to a fourth embodiment, wherein a light source unit comprises a first light source module similar to that shown in  FIG. 2 , together with a second light source module; 
         FIG. 7  shows an output spectrum of the second light source module shown in  FIG. 6 ; 
         FIG. 8  illustrates schematically an illumination system according to a fifth embodiment wherein the light source unit comprises a first light source module and a second light source module; 
         FIG. 9  shows the spectral output of the first and second light source modules of  FIG. 8 : A. without laser pumping of either module, and B. with laser pumping of both modules; 
         FIG. 10  illustrates schematically an illumination system according to a sixth embodiment, similar to that shown in  FIG. 5 , except that the pump laser is coupled by a flexible fiber light guide to the first light source unit. 
         FIG. 11  shows a first arrangement of optical elements for coupling emission of one or more wavelengths, from a light source unit as illustrated in  FIG. 5 , along a primary optical axis to the optical output of the illumination system; 
         FIG. 12  shows a second arrangement of optical elements for coupling emission of one or more wavelengths, from a light source unit as illustrated in  FIG. 10 , along a primary optical axis to the optical output of the illumination system; 
         FIGS. 13A-C  show three configurations of optical elements for coupling of the pump laser to the phosphor layer of the LED1 using respectively:  13 A. a lens;  13 B. a Compound Parabolic Concentrator (CPC); and  13 C. a taper; 
         FIG. 14  shows an arrangement of optical elements for coupling emission of one or more wavelengths, from a light source unit as illustrated in  FIG. 4 , to an optical input of a fluorescence microscope system, using a liquid light guide; 
         FIG. 15  illustrates schematically an illumination system according to another embodiment; 
         FIG. 16  illustrates schematically an illumination system according to yet another embodiment; 
         FIG. 17  illustrates schematically an illumination system according to even another embodiment; 
         FIG. 18  illustrates schematically an illumination system according to still another embodiment; 
         FIG. 19  is a chart showing a prophetic example of optical output vs. intensity setting in an exemplary illumination system with more than one operating mode; 
         FIG. 20  is a schematic representation of another exemplary illumination system; 
         FIG. 21  is a detailed exemplary optical configuration of a light source unit, like the light source unit in  FIG. 20 ; 
         FIG. 22  is a schematic representation of one exemplary alternative configuration for providing laser light that may be used to pump the phosphor in any one of the light source units disclosed herein; 
         FIG. 23  is a schematic representation of another exemplary alternative configuration for providing laser light that may be used to pump the phosphor in any one of the light source units disclosed herein; 
         FIG. 24  is a schematic representation of yet another exemplary alternative configuration for providing laser light that may be used to pump the phosphor in any one of the light source units disclosed herein; and 
         FIG. 25  is a side view of a tapered hexagonal rod, and shows the shape and relative size of opposite ends of the tapered hexagonal rod. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A schematic diagram showing elements of an illumination system  1000 , according to a first embodiment of the invention, is shown in  FIG. 1 . The illumination system  1000  comprises a light source unit or module  100  for providing high brightness illumination for fluorescence illumination and analysis. The light source unit  100  comprises first and second light sources  110  and  120 . The first light source  110  comprises an LED  112  (LED1) and a phosphor layer  114 , the LED  112  emitting a first wavelength λ 1  within an absorption band of the phosphor layer and the phosphor layer  114  emitting broadband light emission of longer wavelength, comprising light in a wavelength band Δλ PHOSPHOR  (abbreviated as Δλ P  in the Figures). The second light source  120  comprises a laser  120  emitting at a second wavelength λ 2 , also within an absorption band of the phosphor layer. The illumination system  1000  also comprises drive means or drive unit, i.e. controller/driver  180  comprising a power supply  182 , LED/laser controller  184  and LED/laser drivers  186 , which are coupled by electrical connections  188  for concurrently driving the LED  110  and the laser  120 , to enable optical pumping of the phosphor layer  114  with the laser  120 , i.e. at the laser wavelength λ 2 . 
     As shown in  FIG. 1 , in a simple arrangement to provide for laser pumping of the phosphor layer, the first and second light sources  110  and  120  are arranged so that the laser  120  illuminates the phosphor layer  114  at an angle, e.g. at grazing incidence, and emission from the LED  112  and the phosphor  114 , comprising wavelengths λ 1  and Δλ PHOSPHOR , that is emitted along a primary optical axis A, is coupled to an optical output  160  of the system. The laser  120  may be coupled to the phosphor layer through a light guide, an optical concentrator or other optical elements (not shown in  FIG. 1 ). 
     The first light source  110  may be a phosphor coated LED, mounted on a suitable heatsink for thermal management, e.g. a phosphor LED which provides high brightness white light illumination, i.e. comprising a blue light emitting LED  112  having a deposited phosphor coating  114  providing emission over a desired wavelength band Δλ PHOSPHOR  in the longer wavelength visible range. Under normal operation of the first light source  110 , even when the LED  112  is driven at higher current or voltage (i.e. the maximum driving current is limited by a maximum driving current density), the phosphor layer  114  is not saturated by the blue light emission from LED  112 . Thus, supplementary optical pumping of the phosphor  114 , using the pump laser  120 , significantly increases the optical output of the phosphor emission band Δλ PHOSPHOR . The pump laser wavelength λ 2  may be the same or different from the LED wavelength λ 1 , provided it is also within the absorption band of the phosphor layer  114 . 
     Thus, under normal operation, without laser pumping, driving the LED  112  generates light from the LED itself at wavelength λ 1  together with emission in the emission band of the phosphor Δλ PHOSPHOR . By concurrently optically pumping the phosphor with the laser wavelength λ 2 , the optical output in the emission band of the phosphor Δλ PHOSPHOR  is increased significantly, as will be further explained below with reference to  FIGS. 2, 3 and 4 , and subsequent Figures. 
     A preferred arrangement for high brightness illumination systems for fluorescence imaging and analysis, comprises two or more light source modules, i.e. providing different output wavelengths, and optical elements for coupling outputs from the two or more light source modules along a primary optical axis to the optical output of the system. 
     Thus, a schematic diagram showing elements of an illumination system  1000 - 1 , according to a second embodiment of the invention, is shown in  FIG. 2 . The illumination system  1000 - 1  comprises a light source unit or module  100 - 1  for providing high brightness illumination for fluorescence illumination and analysis. The light source unit  100 - 1  is similar to that shown in  FIG. 1 , in that it comprises first and second light sources  110  and  120 . The first light source  110  comprises an LED  112  (LED1) and a phosphor layer  114 , the first LED  112  emitting at a first wavelength λ 1  within an absorption band of the phosphor layer and the phosphor layer  114  emitting broadband light emission of longer wavelength, comprising light in a wavelength band Δλ PHOSPHOR  (abbreviated as Δλ P  in the Figures). The second light source  120  comprises a laser  120 , preferably a solid state laser diode, emitting at a second wavelength λ 2 , also within an absorption band of the phosphor layer. Also provided is a dichroic element, i.e. a beam-splitter/combiner,  116  (D 1 ), which reflects the laser wavelength λ 2  to couple the pump laser excitation to the phosphor layer, and transmits λ 1  and Δλ PHOSPHOR . That is, for the arrangement shown in  FIG. 2 , the dichroic beam-splitter/combiner has a band edge λ D  between λ 1  and λ 2 . Thus the combined emission from the LED  112  and the phosphor  114 , λ 1  and Δλ PHOSPHOR , is coupled, along the primary optical axis A, to the optical output  160 . Optionally, another light source  100 - 2 , i.e. comprising an LED  130  (LED3) emitting another wavelength band λ 3  may be provided and the dichroic beam-splitter/combiner  116  is also used to couple λ 3  to the primary optical axis. 
     Preferably, other optical coupling elements such as lenses or optical concentrators are also provided for more efficiently coupling the laser emission λ 2  to the phosphor, and for collecting the light emission λ 1 +Δλ PHOSPHOR , and coupling this light emission, to an optical output  160  of the light source unit  100 . However, for simplicity these additional optical elements are not shown in  FIG. 2 , and they will be described in more detail below with reference to  FIGS. 11 to 14 . By way of example only, the first light source  110  comprises, a low cost, commercially available “white light” solid state light source i.e. a “white light LED” comprising a phosphor layer  114  pumped by a blue light LED  112 , which is manufactured for the demands of general high brightness lighting. One example is a PhlatLight® White LED manufactured by Luminus Devices, which comprises a blue light emitting LED and a Ce:YAG type phosphor coating that provides an emission spectrum, such as illustrated in  FIG. 3 , spectrum B. The spectrum comprises a strong blue light peak in a first spectral region λ 1  at around 450 nm from LED1 and a broad emission band Δλ PHOSPHOR  from 500 nm to 700 nm at longer wavelengths that peaks in the 530 nm to 630 nm region of the spectrum. Thus under normal operation, i.e. when electrically driven at a suitable current and voltage, the resulting light emission, λ 1  and Δλ PHOSPHOR , combines to provide a white light spectrum, spectrum B. With supplementary optical pumping by laser  120  at λ 2 , i.e. at 440 nm as shown in spectrum C, in the absorption band of the phosphor (spectrum E), the laser pumped emission spectrum shows increased intensity in the broad emission band Δλ PHOSPHOR  of the phosphor, as shown by spectrum A. That is, spectrum A comprises emission from LED1 at λ 1  at 445 nm to 475 nm, at a similar intensity as in spectrum B, with a much stronger peak Δλ PHOSPHOR  between 500 nm and 750 nm, peaking at around 530 nm to 630 nm. 
       FIGS. 3 and 4  demonstrate that under normal operation of this phosphor based LED  110 , even when driven at higher current or voltage (i.e. the maximum driving current is limited by a maximum driving current density), the phosphor layer  114  is not saturated by the blue light emission from LED  112 . Thus, supplementary optical pumping of the phosphor  114  using the pump laser  120  significantly increases the optical output Δλ PHOSPHOR  from the phosphor at longer wavelengths, as shown by comparing the emission spectra A and B, in  FIG. 3 . In particular, by selecting an appropriate phosphor LED  110 , having a phosphor emission in the 500 nm to 700 nm range, and preferably having a peak in the range from 530 to 630 nm, high brightness illumination can be provided at these wavelengths, i.e. even within the green gap. 
       FIG. 4  shows the optical output of light source module  100 - 1  as a function of LED drive current with and without supplementary laser optical pumping of the phosphor layer. That is,  FIG. 4  compares the optical power at the objective plane of a fluorescence imaging system, when operating the white light LED with and without laser pumping, using a 40× objective and an excitation filter to provide an illumination band from 545 nm to 575 nm. For operation at the maximum driving current, with laser pumping, the output of the light source unit  100  in this wavelength band was increased 2-3 times at the maximum driving current, compared to operation of the same white light phosphor LED  110  without supplementary laser pumping of the phosphor layer. 
     Thus, by way of example, the light source module  100 - 1  for illumination system  1000 - 1  comprises a first light source  110  comprising the LED1  112  emitting λ 1  in the range 445 nm to 475 nm having a phosphor  114  emitting Δλ PHOSPHOR  in the range 500 nm to 750 nm, which is pumped by the second light source  120  comprising the laser emitting λ 2  at 440 nm. The band edge wavelength λ D  of the dichroic element is selected at 443 nm, i.e. between λ 1  and λ 2 , and arranged to reflect the laser wavelength λ 2 , and transmit λ 1  and Δλ PHOSPHOR . Thus, the optical output of the illumination module  100  comprises λ 1 +Δλ PHOSPHOR . 
     Referring again to  FIG. 2 , optionally, if it is required to provide another light source  100 - 2 , i.e. comprising an LED  130  (LED3) emitting another wavelength band λ 3 , the dichroic beam-splitter/combiner  116  provides a compact and convenient way to couple light of wavelength λ 3  from LED  130  to the primary optical axis. As illustrated, the dichroic beam-splitter/combiner  116  has a pass band edge selected to reflect the laser emission at the laser wavelength λ 2 , and transmit emission at λ 1  from the LED  110  and Δλ PHOSPHOR  from the phosphor, and also reflect λ 3 , the output emission comprises λ 1  and Δλ PHOSPHOR  and λ 3 . Thus, the combined optical output λ 1 +Δλ PHOSPHOR , and optionally λ 3 , of the illumination system can be coupled to the optical input of a fluorescence imaging and analysis system, such as a slide scanner or fluorescence microscope, with suitable coupling optics (not shown in  FIG. 2 , see  FIGS. 11 to 14 ). As is conventional, filters within the fluorescence imaging system provide for selection of appropriate wavelengths for broadband or narrowband illumination, e.g. standard wavelength bands for fluorescence analysis, just as they would be if a conventional lamp illumination system was used. Beneficially, the solid state illumination system of the embodiment not only provides high radiance illumination at selected wavelengths, but also provides other advantages of solid state light sources over conventional lamps, i.e. electronic control of illumination parameters, such as, intensity and pulse duration. 
     An illumination system  2000  according to a third embodiment is shown in  FIG. 5 . The light source unit  200  comprises a first light source module  100 - 1 , comprising first and second light sources  110  and  120 , identical to module  100 - 1  shown in  FIG. 2 . Like parts are labeled with the same reference numerals in each Figure. Additionally, a second light source module  100 - 2  comprises two additional light sources  100 - 2  and  100 - 3 , i.e. a LED or LED arrays  130  and  140  for light emission at other wavelengths. A second dichroic element, i.e. beam-splitter/combiner  118  is provided, which has a band edge selected to combine the output of LED3 and LED4. That is, a LED  130  (LED3) provides light emission at λ 3 , and a LED  140  (LED4) provides light emission at wavelength λ 4 . For example, LED3 and LED4 may provide near ultraviolet (near UV) emission and UV emission respectively. 
     The drive system  180  is similar to that shown in  FIG. 1 , comprising a power supply  182 , LED/laser controller  184  and LED/laser drivers  186  for driving each of the LED light sources, i.e. LEDs  110 ,  130  and  140  and laser  120 . The additional dichroic element  118  is provided for coupling the output from the third and fourth light sources  130  and  140 , and then combining other wavelengths, via the first dichroic element  116 , along the primary optical axis, to couple each of the combined wavelengths, λ 1 , Δλ P , λ 3  and λ 4 , to the output  160  of the light source unit  200 . 
     For example, the first light source  110  may comprise a blue light emitting LED  112  emitting a wavelength λ 1  in the range from 445 nm to 475 nm, with a phosphor layer  114  emitting in Δλ PHOSPHOR  in the 530 nm to 630 nm band. The second light source  120  comprises a laser emitting at λ 2 , i.e. at 440 nm in the absorption band of the phosphor layer  114 , and the dichroic element  116  has a 443 nm edge, i.e. as described with respect to the light source unit  100 - 1  shown in  FIG. 2 . To provide a combined UV/near UV illumination band, LED  130  comprises a near UV LED (LED3) providing near UV emission at λ 3 , e.g. 410 nm to 445 nm, and LED  140  comprises a UV LED (LED4) providing UV emission at λ 4 , e.g. 370 nm to 410 nm or 350 nm to 390 nm. In the configuration illustrated in  FIG. 5 , the second dichroic element  118  is provided which has a band edge to reflect the shorter wavelength UV emission at λ 4  from LED4 and transmit the longer wavelength emission λ 3  from LED3. The emission λ 3 +λ 4  is reflected by the first dichroic element  116  and redirected to the optical output  160 . That is, LED3 and LED4 can cover wavelengths in the near UV and UV bands which are reflected by the first dichroic element  116 , i.e. wavelengths shorter than the 443 nm band edge. Thus, the illumination system  2000  provides for high brightness illumination covering the UV, near UV, blue, green, yellow and red, to the near infrared regions. With suitable choices of λ 1 , λ 2 , Δλ PHOSPHOR , λ 3 , λ 4 , the system can provide sufficient intensity at each wavelength commonly used for fluorescence imaging and analysis. 
     An illumination system  3000  according to a fourth embodiment is shown in  FIG. 6 . This system comprises a first light source module  100 - 1  identical to unit  100 - 1  shown in  FIG. 2  and module  100 - 1  shown in  FIG. 5 . Thus, it comprises a first light source  110  comprising LED  112  (LED1) and its phosphor layer  114  (Phosphor1) and a second light source comprising the pump laser  120 , providing output emission at λ 1  and Δλ P1 . The second light source  100 - 2  module comprises a LED  140  (LED4) and a different phosphor layer  124  (Phosphor2). For example, to provide a UV and near UV band, LED 4 comprises a UV LED, providing UV emission λ 4  at 370-410 nm or 350-390 nm, for exciting Phosphor2. Phosphor2 provides a near UV emission band, Δλ P2 , e.g. 410-445 nm. A sample emission spectrum of the second illumination module, comprising λ 4  and Δλ P2 , is shown in  FIG. 7 . As explained with reference to  FIG. 5 , since λ 4  and Δλ P2  are shorter than the 443 nm band edge of the dichroic element  116 , they will be reflected and redirected to the optical output  160  of the illumination unit. 
     An illumination system  4000  according to a fifth embodiment is shown in  FIG. 8 . An illumination unit  400  comprises first and second illumination modules  100 - 1  and  100 - 2 . The first illumination module  100 - 1  is identical to module  100 - 1  illustrated in  FIGS. 2 and 5 . The second illumination module  100 - 2  is a similar laser pumped phosphor LED, i.e. phosphor LED  130 , comprising LED  140  (LED4) emitting λ 4 , phosphor layer  124  (Phosphor2) emitting Δλ P2 , and a pump laser  150  emitting laser wavelength λ 5 . In this embodiment, to provide a UV and near UV band and λ 4  and Δλ P2 , the light source module  100 - 2  comprises LED4 emitting in a UV band, e.g. 375-410 within an absorption band of Phosphor2, and Phosphor2 emitting in the near UV band, e.g. 410-445 nm. The dichroic element  118  is positioned to reflect the pump laser emission at λ 5  and transmit the LED4 emission at λ 4 . That is, second dichroic element  118  has a passband edge between the LED5 laser wavelength λ 5  and the LED4 wavelength λ 4 , e.g. 373 nm. The resulting output emission spectrum of system  4000  is shown in  FIG. 9 : spectrum A: without laser pumping of light source module  100 - 1  or  100 - 2 ; and spectrum B: with laser pumping of both modules  100 - 1  and  100 - 2 . These spectra demonstrate the significant increase in emission intensity of both Phosphor 1 and Phosphor2 emission, with laser pumping. 
     An illumination system  5000  according to a fifth embodiment, comprising a light source unit  500  is illustrated in  FIG. 10 . This system is similar to that shown in  FIG. 5 , and all like components are labeled with the same reference numerals. This embodiment differs from that shown in  FIG. 5  in that the pump laser  120  (Laser2) is housed within the control unit  180  instead of within the light source unit  500 . The output of the pump laser is coupled by a flexible light guide  190  to an input  162  of the light source unit  500 , and then directed by the dichroic element  116  for pumping of the phosphor layer  114 . 
     In each of the embodiments described above, the pump laser system  120  may comprise a solid state laser, e.g. a single laser diode or a laser diode array. Each LED light source may comprise a single LED or a LED array. The phosphor layer for LED1 is integrated with LED1, i.e. a direct die contact layer or coating deposited on LED1, or a phosphor suspended in an encapsulant such as silicon, also in direct contact with LED1. The Phosphor2 layer for LED4 is similarly integrated with LED4. In a variation of the module  100 - 2  shown in  FIG. 6 , Phosphor1 or Phosphor2 may be a remote phosphor layer, e.g. a phosphor coating on a separate substrate, pumped by (non-laser) LED1 or LED4. While specific arrangements of dichroic elements, i.e. beam-splitters and combiners, have been described it will be appreciated that other arrangements of these elements can be provided. In particular the wavelengths of each light source element may be combined or split by suitable choices of the bandpass or band edge of each dichroic element. 
     To simplify optical coupling, it is preferable that each dichroic element is selected to reflect the pump laser wavelengths, i.e. λ 2  or λ 5 , in the embodiments described above. Additionally, to provide for effective optical coupling of the pump laser to the phosphor layer and efficient collection of the light emission from each light source, optical coupling elements such as lenses or optical concentrators are used. For simplicity these elements are not shown in the preceding Figures.  FIGS. 11 to 14  show further details for arrangements of these optical coupling elements, by way of example. 
       FIG. 11  shows an arrangement of optical coupling elements for the system illustrated in  FIG. 5 . Like parts are labeled with the same reference numerals. For thermal management, the phosphor LED  110  comprising LED  112  (LED1) and phosphor layer  114  is mounted on a copper plate  119  which is cooled by water or forced air. Focusing and collection optics comprise lens  122 , which collects light emission from the pump laser  120 . The pump laser light λ 2  is reflected from dichroic element  116 , and collected by collection lens  124  to focus the pump laser light λ 2  onto the phosphor layer  114 . Light emission at λ 1  and Δ PHOSPHOR  is collected by collection lens  124 , transmitted by the dichroic element  116  and collimated by output coupling lenses  126  for coupling to the optical output  160  of the illumination system, e.g. to an optical input of a fluorescence imaging and analysis system or to an optical input of a microscope (not shown). Emission from the LEDs  130  and  140  is collected by lenses  132  and  142 , respectively, and coupled through the second dichroic plate  118 , the first dichroic plate  116  and the output coupling lenses  126  to the optical output  160 . 
       FIG. 12  shows an arrangement of optical coupling elements for a system such as illustrated in  FIG. 10 . This arrangement is similar to that shown in  FIG. 8 , except that the pump laser  120  is housed externally of the light source unit, for example within the control unit  180  as shown in  FIG. 8 , and the pump laser radiation is coupled to an input  162  of the light source unit  500  via a flexible optical light guide  190 . 
       FIGS. 13  A, B and C show three variants of the arrangement of optical coupling elements shown in  FIG. 10 . In  FIG. 13B  the coupling lens  124 A of  FIG. 13A  is replaced by a compound parabolic concentrator  124 B, and in  FIG. 13C  a conical tapered concentrator  124 C is used. Other optical coupling elements are similar to those shown in  FIG. 11 . 
     In various implementations (including those described throughout this application), any one of these optical coupling elements (e.g., coupling lens  124 A, compound parabolic concentrator  124 B, or tapered concentrator  124 C, etc.) can positioned relative to the phosphor as shown in  FIGS. 13A, 13B , or  13 C. More specifically, in any of the implementations disclosed herein, a coupling element (e.g., coupling lens  124 A, compound parabolic concentrator  124 B, or conical tapered concentrator  124 C, etc.) can be positioned adjacent to or in contact with the phosphor and arranged so that light being directed toward the phosphor (e.g., from a pump laser) and light emitted by the phosphor passes through the coupling element. 
     In some implementation, the optical coupling element may be a non-conical tapered concentrator, such as a tapered hexagonal or square rod. One example of a tapered hexagonal rod is shown in  FIG. 25 . More specifically,  FIG. 25  shows the tapered nature of the rod and the hexagonal shape of each end. Since the rod is tapered, one end (with a dimension from one flat face to an opposite flat face of “A 1 ”) is dimensionally smaller than the other end (with a dimension from one flat face to an opposite flat face of “A 2 ”). In an exemplary implementation, a tapered rod (hexagonal or otherwise) may have a dimensional ratio of A 1 /A 2  of between 1/3 and 1/2, with a length of between 40 and 50 millimeters. 
     In another variant of the optical coupling elements, shown in  FIG. 14 , the optical emission transmitted or reflected towards the optical output is collected by output coupling lens  126  and focused onto the input of an optical light guide  192 , which may be a liquid light guide, for coupling to an input coupling lens  128  of a fluorescence imaging system, such as a fluorescence microscope or slide scanner. Again, other optical coupling elements are similar to those shown in  FIG. 11  and are labeled with like reference numerals. 
     In summary, a solid state high radiance illumination source as disclosed herein is capable of providing for high intensity illumination at each of a number of wavelengths commonly used for fluorescence analysis and imaging. The laser pumped LED and arrangement of optical components provide for a compact light source unit that may comprise one or more individual LED light sources or LED light source modules, providing different wavelength outputs. The system provides an alternative to conventional arc lamps, and addresses limitations of other available solid state LED light sources to provide high brightness at selected wavelengths, particularly in the 530 nm to 630 nm range. 
     The high radiance solid state illumination system also provides advantages over conventional lamp illumination sources, for example, allowing for electronic control of intensity and pulse generation as disclosed in PCT International patent application no. PCT/CA2012/00446 entitled “Light Source, Pulse Controller and Method for Programmable Pulse Generation and Synchronization of Light Emitting Devices”. 
       FIG. 15  is a schematic representation of an exemplary illumination system  6000  (e.g., for fluorescence imaging and/or analysis). The system  6000  is similar in some ways to the system  2000  in  FIG. 5 . The illustrated system  6000  has a control unit  180 , a light source unit  200 , and a user interface  181 . 
     The light source unit  200  includes a first light source module  100 - 1  (with a first light source  112 , a phosphor light source  114 , a second light source  120 , and a first dichroic optical element (D 1 )  116 ), a second light source module  100 - 2  (with a third light source  130 ), a third light source module  100 - 3  (with a fourth light source  140 ) and a second dichroic element (D 2 )  118 . Each of the first, second, third, and fourth light sources  112 ,  120 ,  130  and  140  in the illustrated implementation is a light emitting diode (LED). Of course, in various implementations, any or all of these may be a different kind of light source. In some implementations, any or all of these may be a laser. In one exemplary alternative configuration, the second light source  120  is a laser, while the first light source  112 , the third light source  130 , and the fourth light source  140  are light emitting diodes. 
     The control unit  180  has a power supply  182 , a controller  184  and drivers  186 , which are coupled by electrical connections  188  to the light source unit  200 . The control unit  180  is generally adapted to control the light source unit  200 . 
     In various implementations, including the one shown in  FIG. 15 , the phosphor light source  114  is a physically attached to the first light source  112  (e.g., as a layer of phosphor applied to a surface of the first light source  112 ). In other implementations, the phosphor light source  114  is physically separate from the first light source  112 . If physically separate, the phosphor light source  114  may take the form of a ceramic or single crystal phosphor substrate, for example. 
     The first light source  112  is configured to emit light at a first wavelength λ 1  within an absorption band of the phosphor light source  114 . The second light source is configured to emit light at a second wavelength λ 2  also within the absorption band of the phosphor light source  114 . The third light source  130  is configured to emit light at a third wavelength λ 3 . The fourth light source  140  is configured to emit light at a fourth wavelength λ 4 . The phosphor light source  114  is configured (e.g., when being pumped or excited) to emit light having a wavelength in a wavelength band Δλ PHOSPHOR . In a typical implementation, the wavelength of light emitted by the phosphor light source  114  is longer than the first wavelength λ 1 . 
     The controller  180  is configured to drive the first, second, third and/or fourth light sources, concurrently or otherwise. For example, in some implementations, the controller  180  is adapted to drive the first light source  112  and the second light source  120  to pump the phosphor light source  114  concurrently. In some implementations, the controller  180  is adapted to drive only one of the first light source  112  or the second light source  120  at a given time to pump the phosphor light source, without concurrently driving the other. For example, in one implementation, the controller  180  is adapted to drive the second light source  120  to optically pump the phosphor light source  114  without concurrently driving the first light source  112  to optically pump the phosphor light source  114 . In a typical implementation, one or more (or both) of the third light source  130  and fourth light source  140  are configured to operate while the phosphor light source  114  is being pumped. 
     The first dichroic optical element (D 1 )  116  in the illustrated implementation is configured to: 1) direct light emitted by the second light source  120  at the second wavelength λ 2  onto the phosphor light source  114 , 2) direct light emitted by the phosphor light source  114  in the wavelength band Δλ PHOSPHOR  (and, optionally, light emitted by the first light source  112  at the first wavelength λ 1 ) to an optical output  160  of the illumination system, 3) direct light emitted by the third light source  130  at the third wavelength λ 3  to the optical output  160  of the illumination system, and 4) direct light emitted by the fourth light source  140  at the fourth wavelength λ 4  to the optical output  160  of the illumination system. 
     The second dichroic optical element (D 2 )  118  in the illustrated implementation is configured to: 1) direct the light emitted by the third light source  130  at the third wavelength λ 3  to the first dichroic optical element (D 1 )  116 , and 2) direct the light emitted by the fourth light source  140  at the fourth wavelength λ 4  to the first dichroic optical element (D 1 )  116 . 
     Light emitted from each respective one of the first, second, third and fourth light sources  112 ,  120 ,  130 ,  140  follows a particular path through the illustrated light source unit  200 . In this regard, light from the first light source  112  (if energized) is directed onto the phosphor light source  114  and travels through the first dichroic optical element (D 1 )  116  to the optical output  160 . Light from the second light source  120  is directed by the first dichroic light source (D 1 )  116  onto the phosphor light source  114 . Light from the phosphor light source  114  travels through the first dichroic optical element (D 1 )  116  to the optical output  160 . Light from the third light source  130  travels through the second dichroic optical element (D 2 )  118  and is then reflected by the first dichroic optical element (D 1 )  116  to the optical output  160 . Light from the fourth light source  140  is reflected by the second dichroic optical element (D 2 )  118  toward the first dichroic optical element (D 1 )  116  and is then reflected by the first dichroic optical element (D 1 )  116  toward the optical output  160 . 
     Thus, in the illustrated implementation, light from the third light source  130  and light from the fourth light source  140  travel between the first dichroic optical element (D 1 )  116  and the second dichroic optical element (D 2 )  118  along a first common optical path. Moreover, light emitted by the first light source  112  (if the first light source  112  is energized), light emitted by the phosphor light source  114 , light emitted by the second light source  120 , light emitted by the third light source  130 , and light emitted by the fourth light source  140  travel from the first dichroic optical element (D 1 )  116  to the optical output  160  along a second common optical path. 
     In some implementations, the illustrated system is operable within and switchable between multiple operating modes. These operating modes can include, for example, any two or more of the following: a first operating mode (e.g., a low power mode) in which only the first light source  112  is optically pumping the phosphor light source  114 , a second operating mode (e.g., a medium power mode) in which only the second light source  120  is optically pumping the phosphor light source  114 , and a third operating mode (e.g., a high power mode) in which the first light source  112  and the second light source  120  are concurrently optically pumping the phosphor light source  114 . In some implementations, the illumination system is switchable between any or all three of these (and possibly more) operating modes. 
     If the system is operable within and switchable between multiple operating modes, in general, the controller  180  typically implements any switching that happens. Moreover, in some implementations, the system has a user interface device  181  (e.g., a knob, toggle switch, touch screen, etc.) that enables a user to specify which of the available operating modes (e.g., low power/intensity, medium power/intensity or high power/intensity) the system should be operating in. In these implementations, the controller  180  can be configured to implement the switching in response to an instruction from the user interface device  181 . In some implementations, the system can be adapted to switch between available operating modes automatically (i.e., without specific input from a human at the time of the switching). In these implementations, the switching may occur automatically in response to a software instruction, a timing signal, or the like. 
       FIG. 16  shows another exemplary illumination system  7000  that is in some ways similar to system  6000  in  FIG. 15 . In system  7000  the second light source  120  is a pump laser (though it could, of course, alternatively, be an LED), and in system  7000  the phosphor light source  114  is physically separate from the first light source  112 . 
       FIG. 17  shows an exemplary illumination system  8000  that is similar in some ways to system  7000  in  FIG. 16 . In system  8000  there is no first light source (e.g.,  120  in  FIG. 16 )—and the phosphor light source  114  is a physically stand-alone component. In the illustrated system  8000 , only the second light source  120  is configured to pump the phosphor light source  114 . 
       FIG. 18  shows an exemplary illumination system  9000  that is similar in some ways to system  6000  in  FIG. 15 . In system  9000 , however, 1) the second light source  120  is a pump laser, 2) there are three (instead of two) dichroic optical elements: a first dichroic optical element (D 1 )  116 , a second dichroic optical element (D 2 )  118  and a third dichroic optical element (D 3 )  119 , and 3) there is an optical filter  121  between the third  119  and first  116  dichroic optical elements. In a typical implementation, the optical filter  121  is configured to filter out a portion of light emitted by the phosphor light source  114 —so that only a portion of the phosphor emission spectrum is combined with the other wavelengths. 
     Due to the extra optical elements and the different overall configuration in system  9000  as compared to the system  6000  in  FIG. 15 , some of the optical light paths that the light from the different light sources follow are somewhat different as well. 
     For example, in system  9000 , light from the first light source  112  is directed onto and pumps the phosphor  114 , travels through the third dichroic optical element  119 , may be (or may not be) partially filtered by the optical filter  121  travels through the first dichroic optical element  116  and through the optical output  160 . Light from the second light source  120  is reflected by the third dichroic optical element  119  onto the phosphor  114  to pump the phosphor  114 . Light from the third light source  130  travels through the second dichroic optical element  118 , is reflected by the first dichroic optical element and travels through the optical output  160 . Light from the fourth light source  140  is reflected by the second dichroic optical element  118  and reflected again by the first dichroic optical element  116  and then travels through the optical output  160 . 
     In various implementations, one or more of the systems disclosed herein may be operable within and switchable between multiple operating modes. These operating modes can include, for example, any two or more of the following: a first operating mode (e.g., a low power mode) in which only a first light source  112  is optically pumping the phosphor light source  114 , a second operating mode (e.g., a medium power mode) in which only a second light source  120  is optically pumping the phosphor light source  114 , and a third operating mode (e.g., a high power mode) in which the first light source  112  and the second light source  120  are concurrently optically pumping the phosphor light source  114 . An illumination system may be switchable between any or all three of these (and possibly more) operating modes. 
     If a system is operable within and switchable between multiple operating modes, in general, the controller  180  typically implements any switching that happens. Moreover, in some implementations, if the system has a user interface device (i.e., device  181  in  FIGS. 15-18 ), the user interface device enables a user to specify which of the available operating modes (e.g., low power/intensity, medium power/intensity or high power/intensity) the system should be operating in. In these implementations, the controller  180  can be configured to implement switching in accordance with or in response to any instructions it receives from the user via the user interface device (e.g.,  181 ). In some implementations, the system can be adapted to switch between available operating modes automatically (i.e., without specific input from a human at the time of the switching). In these implementations, the switching may occur automatically in response to a software instruction, a timing signal, or the like. 
       FIG. 16  is a chart showing a prophetic example of optical output vs. intensity setting (both represented by arbitrary units) in an exemplary illumination system (whose first light source  112  is an LED and whose second light source  120  is a laser, such as shown in  FIG. 8 ) with more than one operating mode. 
     The chart in  FIG. 16  includes information that relates to two operating modes: a first (lower optical output) operating mode, where only the LED  112  is pumping the phosphor material  114 , and a second (higher optical output) operating mode, where only laser is pumping the phosphor material  114 . In some implementations, the system might also have a third (even higher optical output) operating mode, where both the LED  112  and the laser are pumping the phosphor material  114  concurrently (e.g., on opposite sides of the phosphor material  114 ). 
     As shown in the chart of  FIG. 16 , the transition between one operating mode (e.g., the first (lower optical output) operating mode) and another operating more (e.g., the second (higher optical output) operating mode) is substantially linear. In general, this linearity can be achieved by properly calibrating the system (e.g., by ensuring that the user settings correlate with drive currents for the LED and the laser such that the optical output, particularly when transitioning between two different operating modes, is substantially linear). 
     In some implementations, the techniques and systems disclosed herein facilitate generating a relatively large amount of Yellow/Green light without increasing the size of the light emitting area and mixing this with other discrete LED wavelengths to form a broad spectrum light source. In a typical implementation, Yellow light is generated in the phosphor layer (or component) after absorbing blue light, which may be injected from the front of the layer (or component), from the back of the layer (or component), or from both. Also, in some implementations, pump 1 is LED1 and produces a Blue light, the Phosphor Layer is (but need not be) part of LED1, and pump 2 is a laser that produces Blue light. It has been found that, in practice, in some implementations, concurrently pumping the phosphor layer (e.g., with LED1 &amp; a pump laser) may create a high heat load (e.g., on LED1—where the phosphor layer is integrated with LED1) and for many applications the pump laser and phosphor layer provided enough optical power, even when LED1 is not operational. 
       FIG. 20  is a schematic representation of an exemplary illumination system  10000 . The illustrated illumination system  10000  has a light source unit  200 , a drive means or drive unit (i.e. controller/driver)  180  for the light source unit  200 , and a user interface  181 . 
     The light source unit  200  in the illustrated implementation has a plurality of light emitting diodes (LEDs), including LED3, LED4, LED5, LED6, and LED7, a plurality of dichroic optical elements D 1 , D 2 , D 3 , D 3 , D 4 , D 5 , and D 6 , a phosphor light source  114 , and a pump laser  120 . In a typical implementation, the system  10000  also has a plurality of other optical elements (e.g., lenses, collimators, light guides, and the like), which are not shown in  FIG. 20 . 
     During system  10000  operation, one or more (or, more typically, all) of the LEDs (LED3, LED4, LED5, LED6 and LED7) and the pump laser  120  produce light, the dichroic optical elements (D 1 , D 2 , D 3 , D 3 , D 4 , D 5 , and D 6 ), as applicable, collectively direct the light produced by the LED(s) and/or pump laser  120  and into a single system output. 
     In a typical implementation, each respective one of the LEDs (LED3, LED4, LED5, LED6 and LED7) and the pump laser  120  is configured to produce light at a particular wavelength. More specifically, according to the illustrated implementation, LED3 is configured to produce light at one wavelength λ 3 , LED4 is configured to produce light at another wavelength λ 4 , LED5 is configured to produce light at yet another wavelength λ 5 , LED6 is configured to produce light at still another wavelength λ 6 , LED7 is configured to produce light yet another wavelength λ 7 , and the pump laser  120  is configured to produce light at wavelength λ 2 . In a typical implementation, each of these wavelengths (λ 2 , λ 2 , λ 4 , λ 5 , λ 6 , and λ 7 ) is different than the others. However, in some implementations, some of those wavelengths may be the same or similar to others. 
     In a typical implementation, the phosphor light source  114  is configured to fluoresce at a wavelength λ phosphor  when optically stimulated (or pumped) by the pump laser. In a typical implementation, the light produced by the pump laser  120 , at wavelength λ 2 , is within an absorption band of the phosphor light sources  114 . 
     During system  10000  operation, light produced by the pump laser, at wavelength λ 2 , is reflected off of dichroic optical element D 3  toward the phosphor light source  114 . This light, at wavelength λ 2 , causes the phosphor light source  114  to fluoresce, at wavelength λ phosphor . The light from the phosphor light source  114 , at wavelength λ phosphor , passes through dichroic optical element D 3 , is reflected off dichroic optical element D 4 , and passes through dichroic optical element D 1  to the system output. Light from LED5, at wavelength λ 5 , is reflected off dichroic optical element D 5 , passes through dichroic optical elements D 4  and D 1  to the system output. Light from LED6, at wavelength λ 6 , passes through dichroic optical elements D 5 , D 4 , and D 1  to the system output. Light from LED3, at wavelength λ 3 , passes through dichroic optical element D 2 , and is reflected off dichroic optical element D 1  to the system output. Light from LED7, at wavelength λ 7 , is reflected off dichroic optical elements D 6 , D 2 , and D 1  to the system output. Light from LED4, at wavelength λ 4 , passes through dichroic optical element D 6 , and is reflected off dichroic optical elements D 2  and D 1  to the system output. 
     The system  10000  is configured, therefore, such that when all of the LEDs, the pump laser  120 , and the phosphor light source  114  are emitting light, the light exiting the system output is a combination of all the light produced by all of the LEDs and the phosphor light source  114 . Moreover, when any sub-group of the LEDs, the pump laser  120 , and the phosphor light source  114  are emitting light, the light exiting the system output is a combination of all the light being produced by the LED(s) and/or phosphor light source  114  that are emitting light. 
     The control unit  180  in the illustrated implementation has a power supply  182 , an LED/laser controller  184 , and LED/laser drivers  186 . The power supply  182  is generally configured and operable to provide power to other components including, for example, the LED/laser controller  184  and/or the LED/laser drivers  186 . The LED/laser drivers  186  are coupled by electrical connections  188  to the LEDs and to the pump laser  120  in the light source unit  200 . The LED/laser drivers  186  are configured to drive (concurrently or otherwise) every one of the LEDs and the pump laser  120  in the light source unit  200 . The LED/laser controller  184  is generally configured to control operation of the LED/laser drivers  186 . 
     In some implementations, if the system  10000  is operable within and switchable between multiple operating modes (e.g., a low power/intensity mode, a medium power/intensity mode, or a high power/intensity mode), in general, the controller  180  may cause switching between those operating modes. In one exemplary implementation, a low power/intensity mode might call for only one or more (but less than all) of the light emitting components in the light source unit  200  to be operational and, therefore, emitting light. In one exemplary implementation, a high power/intensity mode might call for all of the light emitting components in the light source unit  200  to be operational and, therefore, emitting light. In one exemplary implementation, a medium power/intensity mode might call for operating more light emitting components than the low power/intensity mode calls for, but operating fewer light emitting components than the high power/intensity mode calls for. 
     In some implementations, the user interface  181 , which may be a knob, toggle switch, touch screen, etc., enables a user to specify which of the available operating modes (e.g., low power/intensity, medium power/intensity or high power/intensity) the system  10000  should be operating in. In these implementations, the controller  180  can be configured to implement the switching in response to an instruction from the user interface device  181 . In some implementations, the system can be adapted to switch between available operating modes automatically (i.e., without specific input from a human at the time of the switching). In these implementations, the switching may occur automatically in response to a software instruction, a timing signal, or the like, sometimes without any contemporaneous input from a human user whatsoever. In various implementations, the user interface  181  may provide a user with other ways to access, view and/or enter information into the system. 
     Thus, it can be seen that, in the implementation represented in  FIG. 20 , the first dichroic optical element D 1  is configured to at least direct the light emitted by the phosphor light source  114  at wavelength λ phosphor  to the optical output of the illumination system  10000 . More particularly, in the illustrated implementation, this light, emitted by the phosphor light source  114  at wavelength λ phosphor , passes through the third and fourth dichroic optical elements D 3  and D 4  first before reaching the first dichroic element D 1 , but then is directed, by the first dichroic optical element D 1 , to the optical output of the illumination system  10000 . 
     Moreover, in the implementation represented in  FIG. 20 , the first dichroic optical element D 1  is configured to direct light emitted by the third light source LED3 at the third wavelength λ 3  to the optical output of the illumination system  10000 . In this regard, the light emitted by the third light source LED3 first passes through the second dichroic optical element D 2 , but then is directed, by the first dichroic optical element D 1 , to the optical output of the illumination system  10000 . 
     Additionally, in the implementation represented in  FIG. 20 , the first dichroic optical element D 1  is configured to direct light emitted by the fourth light source LED4 at the fourth wavelength λ 4  to the optical output of the illumination system  10000 . In this regard, the light emitted by the fourth light source LED4 first passes through the sixth dichroic optical element D 6  and is reflected off the second dichroic optical element D 2 , but is then directed, by the first dichroic optical element D 1 , to the optical output of the illumination system  10000 . 
     Moreover, in the implementation represented in  FIG. 20 , the second dichroic optical element D 2  is configured to direct light emitted by the third light source LED3 at the third wavelength λ 3  to the first dichroic optical element D 1 , and to direct light emitted by the fourth light source LED4 at the fourth wavelength λ 4  to the first dichroic optical element D 1 . In this regard, the light emitted by the fourth light source LED4 first passes through the sixth dichroic optical element before reaching the second dichroic optical element D 2 . 
     The various light emitting components in the illustrated light source unit  200  can be adapted to emit light at various wavelengths. In one specific exemplary implementation, λ 2  (from pump laser  114 ) is 450 nanometers, λ 3  (from LED3) is 475 nanometers, λ 4  (from LED4) is 430 nanometers, λ 5  (from LED5) is 635 nanometers, λ 6  (from LED6) is 735 nanometers, λ 7  (from LED7) is 385 nanometers, Δλ phosphor  (the range of wavelengths from phosphor light source  114 ) is 500-600 nanometers. 
     In this specific exemplary implementation, dichroic optical element D 3  may be configured to transmit λ phosphor  (from phosphor light source  114 ), which is 500-600 nanometers, but reflect 445-460 nanometers (e.g., a range that would include the light emitted by pump laser  120 , at λ 2  (e.g., 450 nanometers)). 
     One detailed exemplary optical configuration of a light source unit, like the light source unit  200  in  FIG. 20 , is shown in  FIG. 21 . 
     The optical configuration of the light source unit  200  in  FIG. 21  has a plurality of light emitting diodes (LEDs) including LED3, LED4, LED5, LED6, and LED7, a plurality of dichroic optical elements D 1 , D 2 , D 3 , D 3 , D 4 , D 5 , and D 6 , a tapered optical rod TR, a phosphor light source  114 , a pump laser  120  (e.g., an array of laser diodes), and a plurality of other optical elements, including optical elements OE 1 , OE 2 , OE 3 , OE 4 , OE 5 , OE 6 , OE 7 , OE 8 , and OE 9 . In the illustrated implementation, optical elements OE 1  and OE 2  are configured such that light from the pump laser  120  passes through optical elements OE 1  and OE 2  before reaching dichroic D 3 . Also, in the illustrated implementation, optical element OE 3  is configured such that light from the phosphor, that has passed through the tapered optical rod TR and dichroic D 3  then passes through optical element OE 3 . Moreover, in the illustrated implementation, optical element OE 4  is configured such that light from LED 5 passes through optical element OE 4  before reaching dichroic D 5 . Additionally, in the illustrated implementation, optical element OE 5  is configured such that light from LED 6 passes through optical element OE 5  before it reaches dichroic D 5 . Also, in the illustrated implementation, optical element OE 6  is configured such that light from LED 4 passes through optical element OE 6  before it reaches dichroic D 6 . Additionally, in the illustrated implementation, optical element OE 7  is configured such that light from LED 7 passes through LED 7 before it reaches dichroic D 6 . Moreover, in the illustrated implementation, optical element OE 8  is configured such that light from LED 3 passes through optical element OE 8  before it reaches dichroic D 2 . Finally, in the illustrated implementation, optical element OE 9  is configured such that light passes through optical element OE 9  before passing into a light pipe LP at the output of the light source unit  200 . 
     In various implementations, each optical element OE 1 , OE 2 , OE 3 , OE 4 , OE 5 , OE 6 , OE 7 , OE 8 , and OE 9  may be configured to perform any one or more of a variety of different optical functions. These optical functions may include, for example, collimating, focusing, mixing, etc. As an example, in a typical implementation, including the implementation shown in  FIG. 21 , optical elements OE 1  and OE 2  are configured to collimate and focus. Further, in a typical implementation, the light pipe LP, which can be any kind of integrating rod, taper or light mixer, helps produce better spatial and color uniformity in light exiting the illustrated light source unit  200 . In cross-section, the light pipe LP can have any one of a variety of different shapes including, for example, rectangular, square, hexagonal, etc. The light pipe LP acts as an optical element along the common optical path to collect and mix all wavelengths. Another example of this kind of light pipe is identified as item  192  in  FIG. 14 . The light pipe could be a combination of a hexagonal homogenizing rod+a liquid light guide or fiber light guide. 
     In some implementations, the pump laser  120  and collimating and focusing optics OE 1 , OE 2 , in the light source unit  200  of  FIG. 21  (and/or the pump laser in other light source units disclosed herein), may be replaced with an alternative configuration for providing laser light that may include, for example, an array of laser diodes, or a plurality of linear laser diodes (either directly coupled to an integrated optical rod, or indirectly coupled to an integrated optical rod through one or more mirrors). The tapered optical rod TR can be similar to the element  124   c  in  FIG. 13C , and can have any cross-sectional shape (e.g., circular, rectangular, hexagonal, etc.). 
       FIG. 22  is a schematic representation of one exemplary alternative configuration for providing light (e.g., laser light and/or light within an absorption band of the phosphor light source) that may be used to pump the phosphor in any one of the light source units disclosed herein. The alternative source of laser light in the illustrated implementation includes a 4 by 5 array of laser diodes, together with collimating and focusing optics. Each laser diode in the illustrated array is configured to direct its light into the collimating and focusing optics. If this alternative configuration for providing laser light were placed into the light source unit  200  of  FIG. 21  in place of the pump laser shown in  FIG. 21 , then the light exiting the collimating and focusing optics would head towards dichroic D 3 . 
       FIG. 23  is a schematic representation of another exemplary alternative configuration for providing laser light that may be used to pump the phosphor in any one of the light source units disclosed herein. The alternative source of laser light in the illustrated implementation includes multiple laser diodes, with an integrated rod, together with collimating and focusing optics. More specifically, the illustrated configuration includes two linear laser diodes, side-by-side, and optically (and, optionally, physically) coupled to the integrated rod. The integrated rod, which may be, for example, a light pipe or waveguide is configured to receive the output light from each respective one of the laser diodes. After passing through the integrated rod, the light passes into the collimating and focusing optics If this alternative configuration for providing laser light were placed into the light source unit  200  of  FIG. 21  in place of the pump laser shown in  FIG. 21 , then the light exiting the collimating and focusing optics would head towards dichroic D 3 . 
       FIG. 24  is a schematic representation of yet another exemplary alternative configuration for providing laser light that may be used to pump the phosphor in any one of the light source units disclosed herein. The alternative source of laser light in the illustrated implementation includes multiple laser diodes, a plurality of mirrors, and an integrated rod, together with collimating and focusing optics. More specifically, the illustrated configuration includes three laser diodes, arranged side-by-side relative to one another (though other configurations are possible), and optically coupled, via the plurality of mirrors, to the integrated rod. More specifically, light from each laser diode is directed to a corresponding one of the mirrors, which reflects the light into the integrated rod, which may be, for example, a light pipe or waveguide. After passing through the integrated rod, the light passes into the collimating and/or focusing optics. If this alternative configuration for providing laser light were placed into the light source unit  200  of  FIG. 21  in place of the pump laser shown in  FIG. 21 , then the light exiting the collimating and focusing optics would head towards dichroic D 3 . 
     Although embodiments have been described in detail above by way of example, it will be apparent that modifications to the embodiments may be made. For example, each LED light source referred to as a LED, and it is apparent that each may be a single LED or an LED array of multiple LED, and the phosphor layer may be directly coated on the emitter surface of the LED or LED array, or provided as an overlying phosphor containing layer. For simplicity single optical elements such as lenses are illustrated, but compound lens or other suitable coupling optics may be used. It will also be apparent that additional LED light sources may be added and similarly optically coupled to the optical output using optical coupling elements comprising dichroic beam-splitter/combiners. However, to reduce reflective and transmissive losses, and reduce size and cost, it may desirable to provide a simple design with fewer components. 
     Additionally, various features from different implementations described herein may be combined in ways not explicitly shown in the drawings or otherwise described explicitly. 
     The wavelengths and/or wavelength ranges indicated in this description should not be construed as limiting examples. The wavelengths and wavelength ranges indicated herein may vary. 
     Although embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and not to be taken by way of limitation, the scope of the present invention being limited only by the appended claims.