Patent Description:
Laser systems are presently used in a wide variety of applications. In the past, conventional optically-pumped solid-state lasers utilized broadband arc lamps or flashlamps to laterally or transversely pump the solid-state laser medium in a resonant cavity. Over time diode-pumped solid state laser systems have become the preferred optically-pumped laser systems for most applications.

While presently available diode-pumped solid state laser systems have proven useful in the past, a number of shortcomings have been identified. For example, some high power applications require high power pumping of the laser gain media. Typically, a gain media receives a pump signal within a confined region of a facet formed on the gain media. As a result, undesirable effects such as thermal lensing within the gain media have proven to be problematic. In addition, injecting a seed signal into the gain media within the confines of a compact facet has led to a decrease the operational lifetime of some gain media.

In light of the foregoing, there is an ongoing need for a laser system having a multi-stage amplifier.

An example of a laser system is disclosed in <CIT>. The laser system comprises a laser amplifier including a laser active slab with a source of pump power to amplify an input laser beam, the laser active slab including a block of laser active material designed to minimize parasitic amplified spontaneous emission. The source of pump power may be one or more laser diode bars producing a gain sheet in the laser active slab. Lateral faces may of the slab include optical coatings highly transmitting at a wavelength of the pump power and highly reflecting at a lasing wavelength to provide a folded path for the input laser beam though the gain sheet. The laser amplifier includes external mirrors highly reflecting at the lasing wavelength positioned and oriented to provide one or more additional zig-zag passes through the gain sheet for the input laser beam and to provide a multi-pass-amplified laser.

Various embodiments of laser systems having a multi-stage amplifier are disclosed in herein. In some embodiments, a laser system that utilizes a single multi-pass amplifier for use in various laser systems will be described in detail in the following paragraphs. In other embodiments, a laser system that utilizes a first amplifier and/or pre-amp and at least one multi-pass amplifier for use in various laser systems will be described in detail in the following paragraphs. In one aspect, the present application is directed to a laser system disclosed in claim <NUM>.

Preferred embodiments of the laser system are disclosed in the dependent claims.

The first mirror and second mirror may comprise a curved mirror configured to reflect the at least one amplifier output signal within the output wavelength range.

Other features and advantages of the laser system having a multi-pass amplifier and method of use as described herein will become more apparent from a consideration of the following detailed description.

The novel aspects of the laser system having a multi-stage amplifier as disclosed herein will be more apparent by consideration of the following figures, wherein:.

Various embodiments of multi-stage laser amplifiers for use in various laser systems will be described in detail in the following paragraphs. <FIG> show various embodiments of laser systems incorporating multi-stage amplifier configurations. As shown in <FIG>, in one embodiment the laser system <NUM> includes at least one seed source <NUM> configured to output at least one seed signal <NUM> to at least one first amplifier stage <NUM>. <FIG> shows the seed source <NUM> outputting a single seed signal <NUM> to a single first amplifier stage <NUM>. In contrast, <FIG> and <FIG> shows a single seed source <NUM> outputting multiple seed signals <NUM> to a multiple first amplifier stages 60a, 60b. In addition, <FIG> shows a single seed source <NUM> outputting a single seed signal to a single first amplifier stage <NUM> which outputs multiple amplified signals <NUM> to multiple <NUM>nd amplifier stages 100a and 100b. In addition, <FIG> shows a single seed source <NUM> outputting multiple seed signals for multiple <NUM>st amplifiers stages a 60a and 60b and multiple <NUM>nd stages 100a and 100b. In addition, as shown in <FIG>, multiple seed sources 20a, 20b may be used to deliver multiple seed signals <NUM> to one or more first amplifier stages 60a, 60b. Those skilled in the art will appreciate that any number of seed sources may be configured to output any number of seed signals to any number of first amplifier stages <NUM>.

As shown in <FIG>, optionally one or more optical systems, devices, or components <NUM> (hereinafter "optical device") may be positioned anywhere within the various embodiments of the laser systems <NUM> shown in <FIG>. More specifically, <FIG> and <FIG> show various embodiments of a laser system having one or more optical systems <NUM> positioned therein, however, it is understood that any number of optical systems and/or device <NUM> may be used throughout the various embodiments of laser systems shown in <FIG>. In one embodiment, the optical device <NUM> comprises one or more wavelength filters. Exemplary wavelength filters include, without limitation, one or more dichroic mirrors, wavelength selective devices, optical filters, and the like. In another embodiment, the optical device <NUM> comprises one or more lenses. In another embodiment, the optical device <NUM> comprises one or more sensors. Those skilled in the art will appreciate that any variety of optical devices may be used in the present laser system, including, without limitations, lenses, filters, mirrors, sensors, modulators, polarizers, waveplates, masks, attenuators, wavelength filters, spatial filters, and the like.

Referring again to <FIG>, the first amplifier stage <NUM> may be configured to receive the seed signal <NUM> from the seed source <NUM> and amplify the seed signal <NUM> to produce at least one amplified seed signal <NUM>. In one embodiment, the first amplifier stage <NUM> is configured to output a single amplified seed signal <NUM> to a single second amplifier stage <NUM> (See <FIG> and <FIG>). In contrast, <FIG> shown multiple first amplifier stages 60a, 60b each outputting a single amplified seed signal <NUM> to a single second amplifier stage <NUM>. In the alternative, <FIG> shows an embodiment of a laser system <NUM> having a single first amplifier stage <NUM> outputting multiple amplified seed signals <NUM> to multiple second amplifier stages 100a, 100b. Any number of first amplifier stages <NUM> may be used within the laser system <NUM>. Further, in the embodiment shown in <FIG>, the multiple first amplifier stages 60a, 60b are shown in a parallel configuration. However, those skilled in the art will appreciate that the first amplifier stages 60a, 60b may be sequentially positioned (in series). Similarly, the various components of the laser system <NUM>, including the seed source 20a, 20b, first amplifier stage 60a, 60b, and/or second amplifier stage 100a, 100b, if present, may be configured in either a parallel architecture or sequentially in a serial configuration or any combination thereof.

As shown in <FIG>, the laser system <NUM> may include at least one second amplifier stage <NUM> therein. In the illustrated embodiment, the second amplifier stage <NUM> may be in communication with one or more first amplifier stages <NUM> positioned within the laser system <NUM>. <FIG> show an embodiment of a laser system having a single second amplifier stage <NUM> positioned therein. Optionally, as shown in <FIG>, various embodiments of laser systems having multiple second amplifier stages 100a, 100b positioned therein. In one embodiment, the second amplifier stages 100a, 100b are in communication with a single first amplifier stage <NUM>. Optionally, multiple second amplifier stages 100a, 100b are in communication with one or more first amplifier stages 60a, 60b (See <FIG>, <FIG> and <FIG>). Any number of second amplifier stages <NUM> may be used in the laser system <NUM>. Further, any number of additional amplifier stages may be used with the laser system <NUM>.

As shown in <FIG>, at least one amplified output signal <NUM> may be emitted from the one or more second amplifier stages <NUM> positioned within the laser system <NUM>. As shown in <FIG>, a single amplified output signal <NUM> is emitted from the second amplifier stage <NUM>. In the alternative, <FIG> show various embodiments of a laser system <NUM> wherein multiple amplified output signals <NUM> are emitted from numerous second amplifier stages <NUM> positioned within the laser system <NUM>. In the illustrated embodiments, the amplified output signal <NUM> is directed into one or more optical systems or devices <NUM> configured to output at least one output signal <NUM>. In one embodiment, optical system <NUM> comprises one or more isolators. In another embodiment, the optical system <NUM> comprises one or more modulators. Optionally, the optical system <NUM> may comprise at least one telescope. Further, the optical system <NUM> may comprise one or more laser systems, amplifiers, and the like. For example, the optical system <NUM> may comprise one or more additional multi-stage amplifiers. The additional multi-stage amplifier <NUM> may include one or more single pass amplifiers. Optionally, the additional multi-stage amplifier <NUM> may include a one or more multi-pass amplifiers. In another embodiment, the optical system <NUM> may include at least one single stage amplifier. Optionally, the optical system <NUM> may include one or more nonlinear optical crystals. Optionally, the laser system <NUM> need not include an optical system <NUM>.

<FIG> shows a schematic view of an embodiment of a seed source <NUM> for use with the laser system <NUM> shown in <FIG>. As shown, the seed source <NUM> includes at least one seed laser <NUM> therein. In one embodiment, the seed laser <NUM> comprises a diode laser system. For example, the seed laser <NUM> may comprise one or more gain switched diode laser system. In another embodiment, the seed laser comprises one or more fiber amplified diode laser sources. Further, the seed source <NUM> may comprise an injection seed diode laser system. Optionally, the seed source <NUM> may comprise one or more fiber lasers devices. In short, any type of laser system may be used as the seed laser <NUM> in the seed source <NUM>.

The seed laser <NUM> may be configured to output at least one seed signal <NUM> having a wavelength from about <NUM> to about <NUM>. For example, in one embodiment, the seed laser <NUM> outputs a seed signal <NUM> having a wavelength from about <NUM> to about <NUM>. For example, the seed signal <NUM> may have a wavelength of about <NUM>. In yet another embodiment, the seed signal <NUM> has a wavelength of about <NUM>. Further, the seed laser <NUM> may be configured to output a pulsed output. For example, the seed laser <NUM> may be configured to output a seed signal <NUM> having a repetition rate of <NUM> or more. In another embodiment, the seed laser <NUM> may be configured to output a seed signal <NUM> having a repetition rate of <NUM> or more. Optionally, the seed laser <NUM> may be configured to output a seed signal <NUM> having a repetition rate of <NUM> or more. For example, the seed laser <NUM> may be configured to output a seed signal <NUM> having a repetition rate of about <NUM>. Optionally, the seed laser <NUM> may be configured to output a seed signal <NUM> having a repetition rate of <NUM>.

Referring again to <FIG>, the seed laser <NUM> may be configured to output a seed signal <NUM> having any desired pulse width. In one embodiment, the seed laser <NUM> may be configured to output a seed signal <NUM> having a pulse width of less than about <NUM> ps. In another embodiment, the seed laser <NUM> may be configured to output a seed signal <NUM> having a pulse width of less than about <NUM> ps. Optionally, seed laser <NUM> may be configured to output a seed signal <NUM> having a pulse width of less than about <NUM> ps. In another embodiment, the seed laser <NUM> may be configured to output a seed signal <NUM> having a pulse width of less than about <NUM> ps. Further, the seed laser <NUM> may be configured to output a seed signal <NUM> having a power of about 1µW to about <NUM>µ W. For example, the seed laser <NUM> may be configured to output a seed signal <NUM> having a power of about <NUM>µ W to about <NUM>µ W. In another embodiment, the seed laser <NUM> may be configured to output a seed signal <NUM> having a power of about 65µ W to about <NUM>µ W.

Referring again to <FIG>, the seed source <NUM> may include one or more optical filters <NUM> configured to filter the seed signal <NUM> to produce at least one filtered or chirped signal <NUM> (hereinafter "filter signal"). In one embodiment, the optical filter <NUM> comprises at least one Bragg reflector. For example, the optical filter <NUM> may comprise at least one chirped fiber Bragg grating. In the illustrated embodiment, the optical filter <NUM> is in communication with at least one sensor or control device <NUM> via at least one conduit <NUM>. For example, during use the control device <NUM> may be configured to permit the user to selectively vary the range of wavelength transmission through the optical filter <NUM>. As such, the wavelength characteristics of the chirped signal <NUM> may be easily varied. Optionally, the optical filter <NUM> may be configured to permit the user to selectively adjust any variety characteristics of the chirped signal <NUM>.

As shown in <FIG>, a first amplifier <NUM> may be included within the seed source <NUM> to amplify the chirped signal <NUM>. In one embodiment, the first amplifier <NUM> comprises at least one fiber amplifier. In one embodiment, the type of first amplifier <NUM> and second amplifier <NUM> (if present) used in the seed source <NUM> may dependent on the type of amplifier stage <NUM> and second amplifier stage <NUM> used in the laser system <NUM>. For example, a Yb:fiber amplifier operating at a wavelength of about <NUM> may be used as the first amplifier <NUM> in the seed source <NUM> if the first and second amplifier stages <NUM>, <NUM> include Yb:YAG. In contrast, a Yb:fiber amplifier operating at a wavelength of about <NUM> may be used as the first amplifier <NUM> in the seed source <NUM> if the first and second amplifier stages <NUM>, <NUM> include Nd:YVO<NUM>. Optionally, any variety of devices may be used in the seed source <NUM>. The first amplifier <NUM> is configured to amplify the signal <NUM> to produce at least one amplified seed signal <NUM>, which may be directed into at least one modulator system or device <NUM>.

Referring again to <FIG>, the modulator device <NUM> is configured to alter the repetition frequency of the pulsed amplified seed signal <NUM> to produce at least one modulated amplified seed signal <NUM>. In one embodiment, the modulator device <NUM> is configured to output a modulated seed signal <NUM> having a repetition rate of about <NUM> to about <NUM>. In another embodiment, the modulator device <NUM> is configured to output a modulated amplified seed signal <NUM> having a repetition rate of about <NUM> to about <NUM>. Optionally, the modulator device <NUM> is configured to output a modulated amplified seed signal <NUM> having a repetition rate of about <NUM> to about <NUM>. For example, the modulator device <NUM> is configured to output a modulated amplified seed signal <NUM> having a repetition rate of about <NUM>. In one embodiment, the modulator device <NUM> is configured to output a modulated seed signal <NUM> having a repetition rate greater than <NUM>. In one embodiment, the modulator device <NUM> comprises an acousto-optic modulator. Optionally, any variety of alternate devices may be used, including, without limitations, electro-optic modulators, amplitude modulators, phase modulators, liquid crystal modulators and the like. In an alternative embodiment seed source <NUM> does not include modulator device <NUM>.

As shown in <FIG>, at least one second amplifier <NUM> may be included within the seed source <NUM> to amplify the modulated amplified seed signal <NUM> to produce at least one amplified modulated signal <NUM>. In one embodiment, the second amplifier <NUM> comprises at least one Yb:fiber amplifier. Optionally, any variety of devices may be used in the seed source <NUM>. For example, solid-state amplifiers may optionally be used in place of or in addition to fiber amplifiers. Further, any number of additional amplifiers may be used in the seed source <NUM>. The amplified modulated signal <NUM> may be directed into at least one isolator <NUM> positioned within or in communication with the seed source <NUM>. In one embodiment, the isolator <NUM> is configured to reduce or eliminate back reflections of the amplified modulated signal output <NUM> in the seed source <NUM>. Those skilled in the art will appreciate that any number of isolators <NUM> may be used anywhere within the seed source <NUM>. The isolator <NUM> may be configured to output at least one seed signal <NUM> to at least one first amplifier stage <NUM> of the laser system <NUM>. In one embodiment, the seed signal <NUM> has a pulse width of about 1ps to about <NUM> ps and a pulse energy of about <NUM>µJ to about <NUM>µJ. For example, the seed signal <NUM> may have a pulse width of about <NUM> ps and a pulse energy of about <NUM>µJ. Further, the seed signal <NUM> may have a repetition rate of about <NUM> to about <NUM> and a power of about 5mW to about <NUM> mW. Optionally, any variety of additional optical elements or devices may be used in the seed source <NUM>, including, without limitations, lenses, mirrors, fold mirrors, planar mirror, curved mirror, dichroic filters, notch filters, gratings, sensors, optical filters, attenuators, modulators, circulators, fiber Brag gratings, laser diodes, volume Bragg gratings, and the like. In the illustrated embodiment, the various components of the seed source <NUM> are positioned within at least one housing <NUM>. Those skilled in the art will appreciate that the various components of the seed source <NUM> may be positioned within multiple housings or may, in the alternative, be located within another subsystem of the laser system <NUM>.

<FIG> shows an embodiment of the first amplifier stage <NUM> shown in <FIG> above. As shown, the first amplifier stage <NUM> may include at least one housing <NUM> configured to contain the various components of the first amplifier stage <NUM> therein. Optionally, the first amplifier stage <NUM> need not include a housing <NUM>. At least one first amplifier pump source <NUM> may be used to generate at least one pump signal <NUM>. In the illustrated embodiment, the first amplifier pump source <NUM> comprises a fiber coupled diode pump source configured to output at least one pump signal <NUM> having a wavelength from about <NUM> to about <NUM>; although those skilled in the art will appreciate that any variety of pump source may be used within the first amplifier pump source <NUM>. In one embodiment, the pump signal <NUM> has a wavelength of about <NUM> to about <NUM>. For example, the pump signal <NUM> may have a wavelength of about <NUM>. In another embodiment, the pump signal <NUM> may have a wavelength of about <NUM>. Optionally, the pump signal <NUM> may have a wavelength of about <NUM>. In another embodiment, the pump signal <NUM> may have a wavelength of about <NUM>. Further, the pump source <NUM> may be configured to output a continuous wave pump signal or, in the alternative, a pulsed pump signal. For example, the pump signal <NUM> may have a repetition rate of about <NUM> to <NUM> or more. For example, in one embodiment the pump signal <NUM> has a repetition rate of about <NUM>. In another embodiment, the pulse signal <NUM> has a repetition rate of about <NUM> to about <NUM>.

Referring again to <FIG>, at least one fiber optic conduit <NUM> may be used to deliver the pump signal <NUM> to a desired location. Optionally, the pump source <NUM> need not include a fiber optic conduit <NUM>. The fiber optic conduit <NUM> terminates with at least one pump signal delivery system <NUM>. In one embodiment, the pump signal delivery system <NUM> comprises a cleaved fiber optic face. In another embodiment, the pump signal delivery system <NUM> may include one or more lenses, mirrors, filters, sensors, positioning devices (such a v-grooves, chucks, and the like), and similar devices. In the illustrated embodiment, at least one optical component <NUM> is coupled to the pump signal delivery system <NUM>, although the pump signal delivery system <NUM> may include such an element therein or may operate without including such a device.

As shown, the pump signal <NUM> is directed out of the pump signal delivery system <NUM>, traverse through at least one reflector <NUM>, and is incident upon at least one gain media <NUM> positioned within the first amplifier stage <NUM>. In one embodiment, the reflector <NUM> comprises at least one dichroic mirror configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. Those skilled in the art will appreciate that any variety of optical reflectors configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM> may be used in the present system. Further, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. In another embodiment, Further, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. In another embodiment, the reflector <NUM> may be configured to transmit multiple optical signals. For example, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>. In another embodiment, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>.

Referring again to <FIG>, optionally at least optical element <NUM> may be positioned anywhere within the first amplifier stage <NUM>. Exemplary optical elements <NUM> include, without limitations, fold mirrors, planar mirror, curved mirrors, lenses, thermal management devices, fans, chillers, filters, and the like. As shown, the pump signal <NUM> traverses through the optical element <NUM> and is incident on the gain media <NUM>. In one embodiment, the gain media <NUM> comprises at least one slab, rod, disk, or similar body constructed of a desired gain material. Exemplary gain materials include, without limitations, Nd:YVO<NUM>, Nd:GdVO<NUM>, Nd:YAG, Nd:YLF, Nd:glass, Yb:YAG, Yb:KGW, Yb:CaF<NUM>, Yb:CALGO, Yb:Lu<NUM>O<NUM>, Yb:S-FAP, Yb:glass, semiconductor gain media, ceramic laser materials, and the like.

As shown in <FIG>, at least one seed signal <NUM> from at least one seed source (See <FIG>) is incident on the gain media <NUM> which amplifies the seed signal <NUM> to output at least one amplified seed signal <NUM>. For example, in one embodiment, a seed signal <NUM> has a pulse width of about <NUM> ps, a pulse energy of about <NUM>µJ, a repetition rate of about <NUM>, and a power of about 5mW to about <NUM> mW prior to amplification. Thereafter, the first amplifier stage <NUM> may be configured to output at least one amplified seed signal <NUM> may having a pulse width of about <NUM> ps, a pulse energy of about <NUM>µJ, a repetition rate of about <NUM>, and a power of about 5W to about <NUM> W to the second amplifier stage <NUM>. Those skilled in the art will appreciate that any number of first amplifier stages <NUM> may be used in the laser system <NUM>.

<FIG> show various embodiments of a second amplifier stage <NUM> for use in a multi-stage amplifier for laser systems. As shown, the second amplifier stage <NUM> may be positioned within housing <NUM> or, in the alternative, may be positioned within the housing of a larger optical system or laser. As shown, the second amplifier stage <NUM> includes at least one gain media device <NUM> therein. In one embodiment, the gain media device <NUM> is Yb:YAG. In another embodiment, the gain media device <NUM> is Nd:YVO<NUM>. Exemplary gain materials include, without limitations, Nd:YVO<NUM>, Nd:GdVO<NUM>, Nd:YAG, Nd:YLF, Nd:glass, Yb:YAG, Yb:KGW, Yb:CaF<NUM>, Yb:CALGO, Yb:Lu<NUM>O<NUM>, Yb:S-FAP, Yb:glass, semiconductor gain media, ceramic laser materials, and the like. In one embodiment, the gain media device <NUM> comprises at least one slab, rod, disk, or similar body constructed of a desired gain material. For example, in the illustrated embodiments, the gain media device <NUM> comprises elongated facets FLon and compact facets FCom. As such, the length of the elongated facets FLon may be greater than the length of the compact facets FCom. In the illustrated embodiments, the energy and/or fluence of the seed signal <NUM> incident on the gain media device <NUM> is more distributed over at least one elongated facet FLon (i.e. transverse pumping) thereby reducing the effects of thermal lensing while reducing the likelihood of damaging the gain media device <NUM>. In the alternative, those skilled in the art will appreciate that the gain media device <NUM> may be seeded via compact facets FCom. In another embodiment, the gain media device <NUM> may be seeded via the elongated facets FLon and compact facets FCom. As a result, those skilled in the art will appreciate that the gain media device <NUM> may be manufactured in any variety of shapes, dimensions, and configurations.

Referring again to <FIG>, the gain media device <NUM> may be proximate to at least one reflector. In the illustrated embodiment, the gain media device <NUM> is positioned between two reflectors <NUM> configured to reflect at least a portion of at least one amplified signal <NUM> from at least one first amplifier stage <NUM> into the gain media device <NUM>. The gain media device <NUM> is configured to be pumped by at least one pump source <NUM>. Optionally, any variety of alternate laser systems may be used to pump the gain media device <NUM>. Further, at least one pump source <NUM> may be configured to output at least one pump signal <NUM> having a wavelength from about <NUM> to about <NUM>. In one embodiment, the pump signal <NUM> has a wavelength of about <NUM> to about <NUM>. For example, the pump signal <NUM> may have a wavelength of about <NUM>. In another embodiment, the pump signal <NUM> may have a wavelength of about <NUM>. Optionally, the pump signal <NUM> may have a wavelength of about <NUM>. In another embodiment, the pump signal <NUM> may have a wavelength of about <NUM>. Further, the pump source <NUM> may be configured to output a continuous wave pump signal or, in the alternative, a pulsed pump signal. For example, the pump signal <NUM> may have a repetition rate of about <NUM> to <NUM> or more. For example, in one embodiment the pump signal <NUM> has a repetition rate of about <NUM>. In another embodiment, the pulse signal <NUM> has a repetition rate of about <NUM> to about <NUM>.

In the illustrated embodiment, multiple fiber coupled diode pump sources <NUM> are configured to provide one or more pump signals <NUM> to the gain media device <NUM>. In the illustrated embodiment, the diode pump source <NUM> is coupled to at least one fiber optic conduit <NUM>. The fiber optic conduits <NUM> may be, but need not be, coupled to one or more pump signal delivery systems <NUM> (See <FIG>). In one embodiment, the pump signal delivery system <NUM> may comprise one or more than one v-grooves or similar positioning features configured to align or otherwise position one or more fiber optic conduits <NUM> in close proximity. In one embodiment the fiber optic conduits <NUM> are separated by a distance less than about <NUM>. In another embodiment the fiber optic conduits <NUM> are separated by a distance greater than about <NUM>. In yet another embodiment the fiber optic conduits <NUM> are separated by a distance of about <NUM>. As such, the fiber optic conduits <NUM> may be positioned so as to produce the output having an elongated profile such as the output of an elongated pump source such as a diode bar, lightpipe, waveguide, or similar structure. As shown in <FIG>, the pump signal delivery system <NUM> may include one or more filters, sensors, lenses and the like, configured to direct the pump signal <NUM> to the gain media device <NUM>. For example, in the illustrated example, one more lenses or similar optical components <NUM>, <NUM> may be used to form a telescope, collimator, homogenizer, diffractive beam shaper, refractive beam shaper, lens array, and the like to condition the pump signal <NUM> for pumping the gain media device <NUM>. In one embodiment, multiple optical components <NUM>, <NUM> may be positioned proximate to multiple fiber optic conduits <NUM> (See Figure <NUM>). In an alternate embodiment, a single optical component <NUM>, <NUM> may be used rather the multiple individual optical components.

As shown <FIG> and <FIG>, the pump signal <NUM> is directed out of the pump signal delivery system <NUM>, traverse through at least one reflector <NUM>, and is incident upon at least one gain media device <NUM> positioned within the second amplifier stage <NUM>. In the illustrated embodiment, the gain media device <NUM> is side-pumped by the pump signal <NUM>. In another embodiment, the gain media device <NUM> is being pumped along an elongated facet of the gain media device <NUM> by the pump signal <NUM>. Optionally, the gain media device <NUM> maybe end-pumped by the pump signal <NUM>. In one embodiment, the reflector <NUM> comprises at least one dichroic mirror (planar or curved) configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. Those skilled in the art will appreciate that any variety of optical reflectors configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM> may be used in the present system. Further, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. In another embodiment, Further, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> there through, while reflecting substantially all light having a wavelength of greater than about <NUM>. In another embodiment, the reflector <NUM> may be configured to transmit multiple optical signals. For example, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>. In another embodiment, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>.

As shown in <FIG>, the reflectors <NUM> receive the amplified seed signal <NUM> and repeatedly direct the seed signal <NUM> into the gain media device <NUM> for multi-pass amplification, thereby outputting an amplified output signal <NUM>. For example, in one embodiment, the amplified seed signal has a pulse width of about <NUM> ps, a pulse energy of about <NUM>µJ, a repetition rate of about <NUM>, and a power of about 5W to about <NUM> W, while output of the second amplifier stage <NUM> has a pulse width of about <NUM> ps, a pulse energy of about <NUM>µJ, a repetition rate of about <NUM>, and a power of about <NUM> W or more.

<FIG> shows an alternate embodiment of reflectors used in the second amplifier stage <NUM>. As shown, the reflectors <NUM> include a substantially planar body wherein at least one reflector is positioned at a slight wedge angle relative to the gain media device <NUM>. In the alternative, <FIG> shows reflectors <NUM> include a substantially curved body. Those skilled in the art will appreciate that the reflectors <NUM> may be manufactured with having any desired shape, size, and configuration. At least one reflector includes areas or regions of high reflectance and areas or regions of high transmission at a desired wavelength formed thereon. For example, <FIG> and <FIG> shows an embodiment of a novel "striped" reflector <NUM> having a reflector body <NUM>. As shown, the reflector body <NUM> includes areas or regions of high reflectance <NUM> at a desired wavelength and areas or regions of high transmission <NUM> at a desired wavelength. During use, the amplified seed signal <NUM> is incident on the reflector body <NUM>. In one embodiment, at least one reflector body <NUM> is aligned such the amplified seed signal <NUM> is incident on the areas or regions of high reflectance <NUM> formed on the reflector body <NUM>. As shown in <FIG>, parasitic signals <NUM> (including Raman-generated signals) formed within the gain media device <NUM> may be incident on the areas or regions of high transmission, thereby permitting the parasitic signals <NUM> to be extracted, suppressed, and/or not reflected by the reflectors <NUM>. The areas of high reflectivity are configured to reflect substantially all the amplified output signal <NUM> through the gain media device <NUM>, while the areas of high transmission are configured to transmit substantially all parasitic signals generated within the gain media device <NUM> as well as unabsorbed amplified seed signal <NUM> and unused pump signal <NUM> (See <FIG>) during use. As shown, parasitic signal or unused signal <NUM> may be transmitted through the reflectors <NUM>. In another embodiment, the reflector <NUM> includes at least one area of high transmission <NUM> formed by applying at least one anti-reflective coating over the reflector body <NUM>. Thereafter, one or more areas of high reflectance <NUM> at a desired wavelength may be formed by selectively applying a wavelength-dependent reflector material over the coated reflector body <NUM>.

Referring now to <FIG>, the gain media device <NUM> receives one or more than one pump signals <NUM> from diode pump sources <NUM>. In one embodiment the diode pump sources <NUM> cause a thermal lens to form in gain media device <NUM> that is substantially in the vertical direction. When amplified seed signal <NUM> passes through gain media device120 multiple times as illustrated in <FIG> and <FIG>, the amplified seed signal <NUM> may be affected by the thermal lens. <FIG> shows the effect of the thermal lens on amplified seed signal <NUM> as it passes through gain media device <NUM> multiple times for three different values of the thermal lens. It is evident that there is substantially one value of the thermal lens (fTL = <NUM>) that results in the size of amplified seed signal <NUM> remaining substantially unchanged as it passes through the gain media device <NUM> and exits as amplified output <NUM>. For any other value of the thermal lens the amplified seed signal <NUM> will change size as it is affected by the thermal lens in gain media device <NUM>. This size change can lead to deleterious effects such as, but not limited to, loss of efficiency from poor overlap with the one or more than one pump beams, beam quality degradation, or even damage if the beam starts to interfere with other components or becomes small enough such as for the case shown in <FIG> where the thermal lens is fTL = <NUM>.

<FIG> shows the variation of amplified seed signal <NUM> size for a substantially fixed thermal lens value fTL = <NUM> for different distances of reflectors <NUM> from the gain media device <NUM>. If in an alternative embodiment, as shown in <FIG>, the distance between reflectors <NUM> and the gain media device <NUM> was increased from about <NUM> to about <NUM>, amplified seed signal <NUM> size would again be substantially constant as it passes through gain media device <NUM> multiple times.

<FIG> shown the variation of amplified seed signal <NUM> size for yet another embodiment where the reflectors <NUM> are curved in the vertical direction. For a thermal lens value of fTL = <NUM> and a separation of about <NUM>, amplified seed signal <NUM> size can again be substantially constant through multiple passes through gain media device <NUM> if the reflectors <NUM> have a curved surface with a radius of curvature of about -<NUM>.

As shown in <FIG>, the mirror or reflector <NUM> includes a reflector body <NUM>. As shown, the reflector body <NUM> includes a large, single area or region of high reflectance <NUM> at a desired wavelength and a single area or region of high transmission <NUM> at a desired wavelength. For example, the area or region of high transmission <NUM> may be configured to transmit substantially all optical signals incident thereon. Further, the area or region of high reflectance <NUM> may be configured to selectively reflect substantially all light having a wavelength of greater than about <NUM> while selectively transmitting light having a wavelength of less than about <NUM> there through. In another embodiment, the area or region of high reflectance <NUM> may be configured to selectively reflect substantially all light having a wavelength of greater than about <NUM> while transmitting all light having a wavelength of greater than about <NUM> there through. Optionally, the area or region of high reflectance <NUM> may be configured to selectively reflect substantially all light having a wavelength of greater than about <NUM> while transmitting all light having a wavelength of less than about <NUM> there through. The reflector <NUM> may be configured to transmit multiple optical signals. For example, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>. In another embodiment, the reflector <NUM> may be configured to transmit at least one optical signal having a wavelength of less than about <NUM> and at least one optical signal having a wavelength of greater than about <NUM>, while substantially reflecting all light having a wavelength of about <NUM>. In another embodiment, the area of high reflectance <NUM> and the area of high transmission <NUM> on the novel reflector body <NUM> may be substantially the same area. More specifically, the reflector <NUM> may comprise a dichroic mirror configured to reflect light within a desired wavelength range (i.e. about <NUM> to about <NUM>) while transmitting light outside the wavelength range there through. In another embodiment, the reflector <NUM> may comprise a notch mirror.

During use, as shown in <FIG>, the amplified seed signal <NUM> is incident on the reflector body <NUM>. As shown, the amplified seed signal <NUM> may be incident along the elongated facet FLon of the gain media device <NUM>. Similarly, the gain media device <NUM> may be pumped along the elongated facet FLon by at least one pump signal <NUM> as described in <FIG>. Further, the angle at which the amplified seed signal <NUM> is incident on the gain media device <NUM> may be selected to optimize the number of passes of the amplified seed signal <NUM> through the gain media device <NUM>. The alignment of at least one reflector body <NUM> may also be configured to optimize the number of passes of the amplified seed signal <NUM> through the gain media device <NUM>. As a result, the gain media device <NUM> may be permeated with the amplified seed signal <NUM>, thereby suppressing the generation of parasitic signals (including Raman-generated signals) within the gain media device <NUM>. The areas of high reflectivity <NUM> are configured to reflect substantially all the amplified output signal <NUM> generated through multiple passes through the gain media device <NUM>. Further, the areas of high reflectance <NUM> are configured to transmit unabsorbed seed signal, unused pump signal <NUM>, and/or parasitic signals generated during the amplification process there through. In the illustrated embodiment, the amplified output signal <NUM> may be extracted from multi-pass amplified <NUM> via at least one area or region of high transmission <NUM> formed on at least one reflector <NUM>.

Claim 1:
A laser system having a multi-pass amplifier system, comprising;
at least one seed source (<NUM>) configured to output at least one seed signal (<NUM>) having a seed signal wavelength;
at least one pump source (<NUM>) configured to provide at least one pump signal (<NUM>) having at least one pump signal wavelength;
at least one first amplifier stage (<NUM>) configured to amplify the at least one seed signal to generate at least one amplified seed signal (<NUM>) in response thereto:
at least one multi-pass second amplifier stage (<NUM>) configured to receive the at least one amplified seed signal;
at least one gain media device (<NUM>) positioned within the at least one multi-pass second amplifier stage, the gain media device having at least one elongated facet and at least one compact facet, the at least one gain media device pumped by the at least one pump signal and configured to receive the at least one amplified seed signal and output at least one amplifier output signal having an output wavelength range;
a first mirror (<NUM>) and at least a second mirror (<NUM>) positioned within the at least one multi-pass second amplifier stage wherein the at least one gain media device is positioned between and separate from the first mirror and at least the second mirror, at least one of the first mirror and at least one second mirror having areas of high reflectivity (<NUM>) at the output wavelength range and areas of high transmission (<NUM>) at wavelengths outside the output wavelength range; wherein the first mirror and the second mirror are configured to receive the amplified seed signal and repeatedly direct the seed signal into the gain media device for multi-pass amplification thereby outputting an amplified output signal (<NUM>) and transmit pump signals for pumping of the gain media;
wherein the areas of high transmission formed on at least one of the first mirror and the at least one second mirror are configured to transmit at least one of the at least one pump signal, at least one unabsorbed seed signal, and at least one parasitic signal (<NUM>) generated during the amplification process:
at least one optical system (<NUM>) in communication with the at least one multi-pass amplifier system and configured to receive the at least one amplifier output signal and output at least one output signal within the output wavelength range.