Abstract:
In general, in one aspect, the invention features a method that includes converting radiation at a first wavelength λ i  to radiation at a second wavelength λ g  and exposing an article to the radiation at λ g  to convert the radiation at λ g  to radiation at a third wavelength λ r  and radiation at a fourth wavelength λ b . λ r  is red radiation, λ g  is green radiation, and λ b  is blue radiation and the article includes lithium tantalate.

Description:
BACKGROUND  
       [0001]     The disclosure relates to color projection displays that utilize a laser radiation source.  
         [0002]     Color displays typically use three complimentary component colors to render a full color image. Conventionally, the component colors are either red, green, and blue or cyan, magenta, and violet. When provided in appropriate ratios, the three component colors combine to provide white light to an observer.  
         [0003]     One type of display is a projection display. In certain embodiments, color projection displays superimpose three different images each composed of a different complimentary color. The result is a full color image. In general, projection displays can use a variety of different light sources. Certain projection displays use one or more lasers as their light source(s).  
       SUMMARY  
       [0004]     In certain aspects, this disclosure relates to a laser source that includes an infrared laser, and one or more nonlinear optical crystals arranged so that radiation from the infrared laser interact with the crystal(s) to emit three beams at an exit end of the crystal(s). The three beams are composed of red, green and blue radiation, respectively. The wavelengths of the colors and the intensity of each beam are arranged so that when the three beams are combined they produce the color of white light, e.g., light resembling warm daylight as defined in the CIE chromaticity diagram.  
         [0005]     In general, in one aspect, the invention features a method that includes converting radiation at a first wavelength λ i  to radiation at a second wavelength λ g , and exposing an article to the radiation at λ g  to convert the radiation at λ g  to radiation at a third wavelength λ r  and radiation at a fourth wavelength λ b . λ r  is red radiation, λ g  is green radiation, and λ b  is blue radiation and the article includes lithium tantalate.  
         [0006]     Implementations of the method can include one or more of the following features and/or features of other aspects. For example, the method can include directing radiation at λ r , λ g , and λ b  out of the article, wherein the radiation directed out of the optical medium at λ r , λ g , and λ b  have respective intensities such that the combined radiation at λ r , λ g , and λ b  directed out of the article corresponds to white radiation. Converting the radiation at λ i  to radiation at λ g  can include exposing another article to the radiation at λ i , wherein the radiation at λ i  interacts with the other article to produce radiation at λ g . The other optical medium can include KTP, LBO, or MgO-doped PPSLT. In some embodiments, λ i =2λ g . The radiation at λ i  can be converted to the radiation at λ g  by second harmonic generation.  
         [0007]     The article can include PPSLT or PPMgSLT. The radiation at λ g  can interact with the article to produce radiation at λ r . The radiation at λ r  can be produced by optical parametric oscillation involving the radiation at λ g  and the article. The optical parametric oscillation can produce radiation at a fifth wavelength, λ nir , where λ r &lt;λ nir . The radiation at λ r  can be produced by optical parametric generation involving the radiation at λ g  and the article. The optical parametric generation can produce radiation at a fifth wavelength, λ nir , where λ r &lt;λ nir .  
         [0008]     Converting the radiation at λ g  to radiation at λ b  can include converting radiation at λ g  to radiation at a fifth wavelength, λ nir , where the radiation at λ g  and λ nir  interact with the article to produce the radiation at λ b . The radiation at λ b  can be produced by sum frequency generation involving the radiation at λ nir  and λ g  and the article.  
         [0009]     The method can include modulating the radiation at λ r , λ g , and λ b  and directing the modulated radiation at λ r , λ g , and λ b  to a viewer.  
         [0010]     In general, in another aspect, the invention features a system that includes a laser configured to produce radiation at a first wavelength λ I , a first article positioned to receive radiation from the laser at λ i  and to convert the radiation at λ i  to radiation at a second wavelength, λ g , a second article comprising lithium tantalite, the second article being positioned to receive the radiation at λ g  and to convert radiation at λ g  to radiation at a third wavelength, λ r , and radiation at a fourth wavelength, λ b . λ r  is red radiation, λ g  is green radiation, and λ b  is blue radiation.  
         [0011]     Embodiments of the system can include one or more of the following features and/or features of other aspects. For example, the laser can be a pulsed laser. λ i  can be infrared radiation. The first article can include KTP, LBO, or PPMgSLT. The second article can include a first portion that includes a plurality of inverted domain regions arranged to produce the radiation at λ r  and radiation at a fifth wavelength, λ nir , when the radiation at λ g  interacts with the first portion. The second article can include a second portion that includes a plurality of inverted domain regions arranged to produce the radiation at λ b  when the radiation at λ nir  and λ g  interacts with the second portion. The first and second portions can have dimensions l 1  and l 2 , respectively, such that a relative intensity of radiation at λ r , λ g , and λ b  exiting the second article in combination corresponds to white radiation. The second article can include opposing faces that are dielectric multilayer coated to form an optical cavity having a resonant wavelength at λ r . The second article can include one or more dielectric-coated mirrors to form an optical cavity having a resonant wavelength at λ r . The lithium tantalate can include PPSLT or PPMgSLT.  
         [0012]     In some embodiments, the system includes a first modulator positioned to receive radiation at λ r  exiting the second article, a second modular positioned to receive radiation at λ g  exiting the second article, and a third modulator positioned to receive radiation at λ b  exiting the second article. The system can include an electronic controller in communication with the first, second, and third modulators, the electronic controller being configured to cause the first, second, and third modulators to modulate an intensity profile of the radiation at λ r , λ g , and λ b , respectively, to form an image at a viewing region.  
         [0013]     In general, in a further aspect, the invention features a system that includes a source configured to provide radiation at a first wavelength λ I , a means for frequency doubling the radiation at λ i  to produce radiation at a second wavelength λ g , a means for parametrically converting radiation at λ g  to radiation at a third wavelength λ r  and a fourth wavelength λ nir , and for converting the radiation at λ g  and λ nir  to radiation at a fifth wavelength, λ b . λ r  is red radiation, λ g  is green radiation, and λ b  is blue radiation. Embodiments of the system can include any of the features of the aforementioned aspects.  
         [0014]     Among other advantages, embodiments feature laser display systems that are relatively simple and compact. For example, laser display systems can be composed of just a few components and fewer adjustable parts. Embodiments of laser display systems do not require additional optics to separate the three complimentary colors. For example, by tilting slightly (e.g., at an angle less than about 5 degrees, less than about 3 degrees, less than about 2 degrees, such as between about 1 and about 2 degrees) the angle between an input beam and an alignment direction of the inverted domains in a nonlinear crystal, the complimentary color beams can naturally exit the crystal in three different directions. No additional dispersive optics are needed to separate the colors.  
         [0015]     Embodiments of laser display systems can be relatively efficient. For example, in some embodiments, the total output power of the display system essentially equals the power of the source (e.g., the exciting laser). The overall wall-plug efficiency can be more than 0.1% (e.g., about 0.5% or more, about 1% or more, about 2% or more, about 5% or more).  
         [0016]     Embodiments of laser display systems can be relatively robust. For example, certain display systems operate above room temperature and are regulated so that temperature fluctuations are relatively small (e.g., regulated to +/−0.15 degrees C.). Being above ambient temperature, embodiments of laser display systems are not substantially affected by changes to the environmental conditions. Furthermore, in embodiments, nonlinear crystals used in laser display systems can have relatively long lifetimes at the elevated temperatures.  
         [0017]     In some embodiments, laser display systems can provide high quality images. For example, embodiments can automatically reduce laser speckle. The process of generating a longer wavelength (e.g., red) beam can be a high gain parametric process, with a relatively high bandwidth and consequently relatively low coherence. Associated complimentary beams (e.g., blue beams) have correspondingly low coherence. Low coherence light in turn results in low speckle. In some embodiments, a random phase plate can be added to other beams to reduce its spatial coherence and corresponding speckle.  
         [0018]     Laser display systems can be readily adapted for dynamic display. For example, in some embodiments, modulators can be positioned in the path of each complimentary beam at the output end of the device, allowing the display system to change the relative intensity of the complimentary beams to produce a display&#39;s visible effect.  
         [0019]     Applications include systems for video display and entertainment (e.g., laser) shows.  
         [0020]     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description, drawings, and the claims. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0021]      FIG. 1  is a schematic diagram of an embodiment of a display system.  
         [0022]      FIG. 2  is a schematic diagram of an embodiment of a component for use in a display system.  
         [0023]      FIG. 3  is a schematic diagram of components of an embodiment of a display system.  
         [0024]      FIG. 4  is a schematic diagram of components of an embodiment of a display system.  
         [0025]      FIG. 5  is a schematic diagram of components of an embodiment of a display system.  
         [0026]      FIG. 6  is a schematic diagram of components of an embodiment of a display system. 
     
    
       [0027]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0028]     Referring to  FIG. 1 , a display system  100  includes a laser  110 , a first non-linear optical medium  114 , a second non-linear optical medium  116 , and three modulator/scanner units  122 ,  124 , and  126 . Laser  110  provides input radiation  111  through element(s)  141  (e.g., a lens, a polarizer, a waveplate, and/or a filter) to first non-linear optical medium  114 . Radiation  113  exits first non-linear optical medium  114 , passes through element(s)  142  (e.g., a lens, a mirror, and/or a filter) and enters second non-linear optical medium  116 , which emits three radiation beams  117 ,  118 , and  119  to modulator/scanner units  122 ,  124 , and  126 , respectively. Modulator/scanner units  122 ,  124 , and  126  direct respective modulated beams  123 ,  125 , and  127  out of display system  100  for display to a viewer. Display system  100  also includes an electronic controller  120  (e.g., a computer processor), which is in communication with modulator/scanner units  122 ,  124 , and  126  and provides information to these units related to the image to be displayed.  
         [0029]     During operation, laser  110  provides radiation  111  at a wavelength λ i . First non-linear optical medium  114  converts a portion of the incident radiation at λ i  into radiation at another wavelength, λ g .  
         [0030]     Radiation  113  at λ i  and λ g  exits first non-linear optical medium  114  and enters second non-linear optical medium  116 , which converts some of the radiation at λ i  and λ g  into radiation at wavelengths λ r  and λ b . These conversion processes are discussed below. Radiation at λ r , λ g , and λ b  exits second optical medium  116  (shown as beams  117 ,  118 , and  119 , respectively) along different paths.  
         [0031]     Beam  117  at λ r  is directed to modulator/scanner  122 , beam  118  at λ g  is directed to modulator/scanner  124 , and beam  119  at λ b  is directed to modulator/scanner  126 . The modulator/scanners encode information into the respective beams, providing modulated beams  123 ,  125 , and  127 , respectively. The information encoded into the beams typically includes spatial and temporal modulations that result in the beams providing an image (e.g., a dynamic image) to a viewing space (e.g., a screen). The information is provided to the modulator/scanners by electronic controller  120 . Examples of modulators/scanners include MEMS devices (e.g., Digital Micromirror Devices (DMD)), scanning mirrors (e.g., mirrors mounted on one or more actuators, such as scanning galvanometers), grating light valves (GLVs), and liquid crystal spatial light modulators.  
         [0032]     Typically, λ r , λ g , and λ b  are at red, green, and blue wavelengths respectively. For example, λ r  is in a range from about 600 nm to about 700 nm, λ g  is in a range from about 500 nm to about 560 nm, and λ b  is in a range from about 400 nm to about 490 nm.  
         [0033]     In general, the relative intensities of the radiation at λ r , λ g , and λ b  in beams  117 ,  118 , and  119 , respectively, can vary. For example, the ratio of intensities at λ r  to λ g  can be greater than 1 (e.g., about 1.2 or more, about 1.4 or more, about 1.5 or more). The ratio of intensities at λ g  to λ b  can be greater than 1 (e.g., about 1.5 or more, about 1.8 or more, about 2 or more, about 2.2 or more). In some embodiments, the ratio of intensities at λ r :λ g :λ b  are about 2:1.4:1. In certain embodiments, the wavelengths and relative intensities are selected so that the combination of the radiation at λ r , λ g , and λ b  corresponds to white light as defined by its CIE chromaticity co-ordinates. For example, the combination of the radiation in beams  117 ,  118 , and  119  can have chromaticity co-ordinates x and y in a range from about 0.25 to about 0.4 (e.g., about 0.33). In some embodiments, the combination of the radiation in beams  117 ,  118 , and  119  provides white light corresponding to a color correlated temperature (CCT) of about 4,800 K or more (e.g., about 5,000 K or more, about 5,200 K or more, about 5,400 K or more, about 5,600 K or more).  
         [0034]     Generally, laser  110  is an infrared laser and radiation  111  is at a wavelength λ i  in a range from about 900 nm to about 2,000 nm (e.g., 1064 nm). λ i  is selected based on the conversion properties of the first and second non-linear optical media so that the output wavelengths of system  100  are at desired wavelengths (e.g., so that the λ r , λ g , and λ b  are red, green, and blue wavelengths, respectively).  
         [0035]     Typically, laser  110  is a pulsed laser, and radiation  111  is emitted in pulses at frequencies in the range of about 1 kHz or more (e.g., about 10 kHz or more, about 20 kHz or more). Pulse duration can vary, and is typically in the range of 1 to 100 nanoseconds (e.g., about 10 nanoseconds), although, in certain embodiments, picosecond and sub-picosecond pulses can be used.  
         [0036]     Further, laser  110  provides radiation  111  at sufficient power to interact with first and second non-linear optical media  114  and  116  to produce the radiation at λ r , λ g , and λ b . For example, in some embodiments, laser  110  can have a peak output power of about 10 kW or more (e.g., about 50 kW or more, about 100 kW or more. As used herein, peak power for a pulsed laser refers to the ratio of the energy per pulse (in Joules) to the pulse duration (in seconds).  
         [0037]     First non-linear optical medium  114  converts radiation at λ i  to radiation at λ g  by a non-linear optical process. In certain embodiments, the conversion process used by medium  114  is second harmonic generation. Accordingly, in these embodiments, 2λ g =λ i . First non-linear medium  114  is composed of material(s) selected based on the desired conversion process and wavelength λ i . First non-linear medium  114  can be composed of Potassium Titanium Oxide Phosphate (KTP), Lithium Triborate (LBO), and/or MgO-doped periodically-poled stoichiometric lithium tantalate (PPMgSLT).  
         [0038]     Second non-linear optical medium  116  converts radiation at λ i  and λ g  to radiation at λ r  and λ b  by one or more non-linear optical processes. In some embodiments, these processes can include optical parametric oscillation which involves transfer of power at λ g  to radiation at wavelengths λ r  and another wavelength λ nir  (e.g., λ nir &gt;λ r ). The non-linear optical process can also include sum frequency generation where power at λ nir  and λ g  are transferred to λ b .  
         [0039]     Second non-linear optical medium  116  is formed from one or more materials selected based on the desired conversion processes and wavelengths of operation of the system. Second non-linear optical medium  116  can be formed, for example, from PPSLT or PPMgSLT.  
         [0040]     In some embodiments, second non-linear optical medium  116  includes an optical cavity for radiation at one or more of wavelengths λ nir , λ r , λ g , or λ b . For example, in some embodiments, non-linear optical medium  116  can have its entry face dielectric multilayer coated for high reflectivity (e.g. &gt;99%) at λ r  and high transmission (e.g. &gt;95%) at λ g  and its exit face dielectric multilayer coated for partial reflectivity (e.g. &lt;100%) at λ r  and high transmission (e.g. &gt;95%) at λ g  and λ b  so that medium  116  forms a monolithic optical cavity and have radiation at λ r , λ g , and λ b  exit as beam  117 .  
         [0041]     In some embodiments, nonlinear optical medium  116  can be placed between elements (e.g., mirrors, such as dielectric multilayer mirrors) that are highly reflective at λ r  in order to increase the intensity of the radiation at this wavelength in second non-linear optical medium  116 . The reflector at the output side of second non-linear optical medium  116  should have a reflectivity less than 100% at λ r  in order to allow radiation at λ r  to exit as beam  117 .  
         [0042]     Referring to  FIG. 2 , in some embodiments, second non-linear optical medium  116  is a non-linear crystal composed of two portions, portion  210  and portion  220 , respectively. Medium  116  has an overall length, L, along one dimension where the length of portion  210  is L 1  and the length of portion  220  is L 2 .  
         [0043]     First portion of length L 1  has domain sections  212  and inverted domain sections  214  periodically arranged along length L 1 . Sections  212  and  214  have a spatial period of λ 1 , where sections  214  have a width δ 1  and sections  212  have a width λ 1 -δ 1 .  
         [0044]     L 1 , λ 1 , and δ 1  are selected to provide gain in a parametric process to provide radiation at λ r  and λ nir  when the first portion is excited by the radiation at λ g . In particular, λ 1  and δ 1  are selected, along with the orientation of second non-linear optical medium  116 , so that quasi phase matching (QPM) is achieved in portion  210 .  
         [0045]     Second portion  220  of length L 2  has domain sections  222  and inverted domain sections  224  periodically arranged along length L 2 . Domain sections  222  and  224  have a spatial period of λ 2 , where sections  224  have a width δ 2  and sections  222  have a width λ 2 -δ 2 .  
         [0046]     In second portion  220 , L 2 , λ 2 , and δ 2  are selected so that the interaction of the radiation at λ nir  and λ g  with the second portion provides radiation at λ b . λ 2  and δ 2  are selected, along with the orientation of second non-linear optical medium  116 , so that quasi phase matching is achieved in portion  220 .  
         [0047]     The lengths L 1  and L 2  are chosen so that the resulting intensities of beams  117 ,  118 , and  119  provide the desired ratios of red, green, and blue (e.g., so that their combination results in the desired shade of white light).  
         [0048]     While the foregoing embodiment of second non-linear optical medium  116  includes periodic inverted domain sections, other configurations are also possible. In general, the sections in either the first and/or second portions can be periodically, aperiodically or quasi-periodically arranged. Periodic arrangements can give the highest parametric gain. However, in certain embodiments, aperiodic or quasiperiodic sections can give better tolerances on the temperature and wavelength stability compared to periodic sections.  
         [0049]     In general, first and second non-linear optical crystals  114  and  116  can be bulk crystals, in the form of a planar waveguide, or in the form of a fiber waveguide.  
         [0050]     In some embodiments, first non-linear optical medium  114  and/or non-linear optical medium  116  are maintained at an elevated temperature (e.g., greater than room temperature). The first and/or second non-linear optical media can be maintained at a temperature of about 100° C. or more (e.g., about 120° C. or more, about 140° C. or more, about 160° C. or more, about 180° C. or more, about 200° C. or more).  
         [0051]     Embodiments can include one or more heaters arranged to heat the first and/or second non-linear optical medium. For example, the first and/or second non-linear optical media can be positioned adjacent an electrical heating element. A thermocouple can be used to monitor the temperature of the first and/or second non-linear optical media and provide feedback to the heater to maintain the media temperature within a desired range.  
         [0052]     As a specific example, laser  110  is a diode-laser-pumped all solid-state Nd:YAG laser that provides infrared pulses of several nanosecond in duration at about 1064 nm (λ i ) and a pulse repetition rate of about 10 kHz or more. The first non-linear optical medium is a type II phase-matched KTP crystal. This frequency doubles the 1064 nm radiation to generate radiation at 532 nm (λ g ). The generated 532 nm light is focused with a lens to a beam waist of about 100 μm into the second non-linear optical medium which is a QPM crystal. The QPM crystal is PPSLT with L 1  of about 2.5 cm having periodically-poled domains with a domain period of about 11.7 μm. L 2  is about 1.5 cm with periodically-poled domains having a domain period of about 8.5 μm. The crystal is about 5 mm wide and about 1 mm thick. The crystal temperature is maintained at about 160° C. The input end of the crystal is dielectric coated for high reflection (e.g., of about 99% or more) at 633 nm, and anti-reflection (e.g., providing reflection of about 1% or less) at 532 nm. The output end of the crystal is coated for about 50% reflecting at 633 nm, and anti-reflection (e.g., providing reflection of about 1% or less) at 532 nm and 460 nm. With these parameters, the output wavelengths are 633 nm (red), 532 nm (green) and 459 nm (blue). Since the crystal does not substantially absorb at any of these wavelengths, the sum of the powers of the three outputs will approximately equal to the power of the input at 532 nm. The ratio of the power of the three colors can be adjusted to the ratio of 2:1.4:1, corresponding to warm daylight color. The intensity of the green input is about 40 MW/cm 2 , which approximately 5 or more times above threshold. This is a level that is substantially safe from optical damage to the crystal surface. While the input beam is generally circularly shaped, it could be oblong with a major-axis to minor-axis ratio of up to about 3 to accommodate higher power applications.  
         [0053]     In system  100 , both first and second non-linear optical media are placed outside of laser  110 . However, in general, other placements of the non-linear optical media are possible. For example, in another variation, the first non-linear optical medium can be incorporated into the laser (e.g., within the optical cavity of the laser). Referring to  FIG. 3 , a display system  300  includes a laser  312 , a first non-linear optical medium  314 , a second non-linear optical medium  316 , and three modulator/scanners  322 ,  324 , and  326 . First non-linear optical medium  314  is positioned within laser  312  and the laser is arranged to emit radiation at λ g  rather than λ i . The operation is otherwise the same as system  100 .  
         [0054]     In certain embodiments, the first and second non-linear optical media can be combined into a single article. For example, referring to  FIG. 4 , a display system  400  includes a laser  412 , a non-linear optical medium  414 , and three modulator/scanners  422 ,  424 , and  426 . Non-linear optical medium  414  includes a first portion that provides the same function as the first non-linear optical medium in system  100 . Non-linear optical medium  414  also includes another portion that provides the function of the second non-linear optical medium in system  100 .  
         [0055]     In general, display systems can include components in addition to those described in relation to systems  100 ,  300 , and  400  above. For example, referring to  FIG. 5 , a display system  500  includes a dielectric mirror  518  positioned between a second non-linear optical medium  516  and modulator/scanners  522 ,  524 , and  526 . System  500  also includes a laser  512  and a first non-linear optical medium  514 . Dielectric mirror  518  is configured to reflect a portion (e.g., about 30% to about 70%) of the incident radiation at λ r , while transmitting substantially all (e.g., about 99% or more) incident radiation at λ g  and λ b . The surface of second non-linear optical medium  516  can be anti-reflection coated for radiation at λ r , λ g , and λ b .  
         [0056]     Other configurations are also possible. For example, referring to  FIG. 6 , a display system  600  includes a laser  612  (e.g., picosecond or subpicoseond high peak power (e.g., &gt;100 kW) laser), a first non-linear optical medium  614 , a second non-linear optical medium  616  aligned with portion L 2  near laser  612  and portion L 1  away from laser  612 , and modulator/scanners  622 ,  624 , and  626 . In addition, display system  600  includes a mirror  618  positioned between laser  612  and the non-linear optical media. Mirror  618  (e.g., a dielectric multilayer mirror) is configured to substantially transmit radiation at λ i , but substantially reflect radiation at λ r , λ g , and λ b . An additional mirror  628  is positioned to direct radiation reflected by mirror  618  towards modulator/scanners  622 ,  624 , and  626 . Further, second non-linear optical medium  616  includes a reflective coating on its surface facing away from laser  612 , which substantially reflects radiation at λ r  and λ g .  
         [0057]     In a specific example, pump laser  612  is a mode-locked solid state laser operating at more than about 10 MHz. In this case, second non-linear optical medium  616 , a QPM crystal, has an anti-reflection coating on the side near L 2 , and is high reflection coated for both the green and the red colors on the side near L 1 . The infrared output from the laser is frequency doubled to the green by first non-linear optical medium  114 , a QPM crystal, and is focused into 2 second non-linear optical medium  616  from the side that is antireflection coated to a Gaussian spot size (waist size) of about 40-60 μm centered at the high reflection face of the crystal. The focused intensity is in a range of about 1-10 GW/cm 2 . In this case the parametric gain is high and second non-linear optical medium operates as a double-pass parametric generator. On the second pass before departing the non-linear optical medium, the residual green frequency mixes with the idler wavelength (λ nir ) generated in the parametric process to produce the blue beam. The red, green and blue beams exit the crystal after two passes of the green in the crystal and are separated from the infrared beam by a dichroic mirror. An advantage of this example is the monolithic crystal can produce a RGB laser beam at multi-MHz repetition rate, suitable for use in laser projection systems that require such high repetition rates.  
         [0058]     While certain embodiments have been described, other configurations are also possible. For example, embodiments can include one or more additional optical components, such as additional lenses, polarizers, waveplates, and/or filters For example, while the foregoing examples produce white light by generating a red, green, and blue beam, in some embodiments other colors can be produced. For example, in some embodiments, the system can be configured to produce cyan, magenta, and yellow beams to provide white light.  
         [0059]     Other embodiments are in the following claims.