Method and system for plasma-electrode pockels cell with vacuum and plasma isolation structures

Abstract

A plasma electrode Pockels cell includes a cathode, an anode, and a set of optical windows disposed between the cathode and the anode and defining a set of plasma chambers. The plasma electrode Pockels cell also includes an electro-optic crystal disposed between the set of plasma chambers, a set of input ports, each of the set of input ports being in fluid communication with one of the set of plasma chambers, a set of electrically insulating vacuum plenums, each of the set of vacuum plenums being in fluid communication with one of the set of plasma chambers, one or more plasma isolation structures disposed in each of the set of vacuum plenums, and a vacuum system in fluid communication with each of the set of vacuum plenums.

Description

METHOD AND SYSTEM FOR PLASMA-ELECTRODE POCKELS CELL WITH VACUUM AND PLASMA ISOLATION STRUCTURESCROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 610,302, filed on December 14, 2023, entitled "Method and System for Plasma-Electrode Pockels Cell with Vacuum and Plasma Isolation Structures," the disclosure of which is hereby incorporated by reference in its entirety for all purposes.STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under DE-FC52-92SF19460 awarded by the Department of Energy. The government has certain rights in the invention.BACKGROUND OF THE INVENTION

[0003] The plasma-electrode Pockels cell (PEPC) is a key enabling technology for high- energy multipass amplifiers. Developed at Lawrence Livermore National Laboratories in the 1980s, the PEPC solves the challenge of optical switching of a large-aperture, high-energy laser pulse by utilizing transparent conductive plasmas as electrodes to apply an electric field across a large-area electro-optic crystal. The electro-optic effect modifies the birefringence of the crystal, modifying the polarization state of the laser pulse as it transits the device. If the applied voltage is equal to the device’s half-wave voltage (ITt), then the PEPC acts a halfwave plate and will produce a rotation of the polarization vector for linearly polarized light.

[0004] Despite the progress made in the area of Pockels cells, there is a need in the art for improved methods and systems related to Pockels cells.SUMMARY OF THE INVENTION

[0005] Embodiments of the present invention relate to optical switches. More particularly, embodiments of the present invention provide methods and systems related to Pockels cellsthat can be integrated into multipass optical amplifiers. In a specific embodiment, a plasma electrode Pockels cell utilizing a novel vacuum plenum including plasma isolation structures is provided. The present invention is applicable to Pockels cells useful in multipass optical amplifiers as well as other optical systems.

[0006] As described herein, a plasma electrode Pockels cell (PEPC) is provided that operates at -100 mTorr with a process gas internal to the PEPC that is ionized to form a plasma. The plasma is highly conductive and energized to ~18-kV potential. As a result, embodiments of the present invention insulate the plasma from conductive material that is electrically grounded. Concurrently, because the PEPC operates at approximately <1 / 1000 of atmospheric pressure, a vacuum system is utilized to maintain the low pressure and remove excess process gas. Traditionally, vacuum system materials consist of electropolished stainless steel that is conductive. The action of pumping the PEPC induces a molecular flow in the vacuum system that cause the plasma in the PEPC to flow toward vacuum system components. In order to prevent the plasma from interacting with conductive components of the vacuum system that can short the plasma to ground, embodiments of the present invention isolate the plasma from conductive components of the vacuum system by stopping or limiting migration of the plasma through the vacuum system, thereby improving the performance of the PEPC.

[0007] Numerous benefits are achieved by way of the present invention over conventional techniques. For example, embodiments of the present invention provide a mid-scale (e.g., 270 mm x 270 mm) PEPC that is capable of optical switching faster than 70 ns and suitable for use in multipass amplifier systems. The PEPC has been demonstrated in a polarimeter system to satisfy switching speed requirements for sufficiently large plasma current. The switching contrast, or extinction ratio, provided by embodiments of the present invention exceeds 1000: 1 throughout the clear aperture. These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. l is a simplified schematic diagram of a multipass amplifier including a plasma-electrode Pockels cell (PEPC) according to an embodiment of the present invention.

[0009] FIG. 2A is a simplified perspective view of a PEPC according to an embodiment of the present invention.

[0010] FIG. 2B is a simplified plan view of the PEPC illustrated in FIG. 2A.

[0011] FIG. 2C is a simplified end view of the PEPC illustrated in FIG. 2A.

[0012] FIG. 3 is a simplified cross-sectional perspective view of a vacuum plenum according to an embodiment of the present invention.

[0013] FIG. 4 is a simplified flowchart illustrating a method of operating a PEPC according to an embodiment of the present invention.

[0014] FIG. 5 is a simplified timing diagram illustrating operation of a PEPC according to an embodiment of the present invention.

[0015] FIG. 6 is a simplified schematic diagram of a test stand for the PEPC according to an embodiment of the present invention.

[0016] FIG. 7A is a plot of transmittance as a function of time for the PEPC according to an embodiment of the present invention.

[0017] FIG. 7B is a plot of six round trip passive transmission as a function of arrival time of the pulse according to an embodiment of the present invention.

[0018] FIG. 8 is a plot of the 1% to 99% switching time as a function of peak current according to an embodiment of the present invention.

[0019] FIG. 9A is a plot of spatially resolved switching contrast measured at the optimum half-wave switch voltage according to an embodiment of the present invention.

[0020] FIG. 9B is a plot of the measured inverse contrast and the predicted curve as a function of switch voltage according to an embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0021] Embodiments of the present invention relate to optical switches. More particularly, embodiments of the present invention provide methods and systems related to Pockels cells that can be integrated into multipass optical amplifiers. In a specific embodiment, a plasma electrode Pockels cell utilizing a novel vacuum plenum including plasma isolation structuresis provided. The present invention is applicable to Pockels cells useful in multipass optical amplifiers as well as other optical systems.

[0022] FIG. l is a simplified schematic diagram of a multipass amplifier including a plasma-electrode Pockels cell (PEPC) according to an embodiment of the present invention. A laser pulse is injected into the multipass amplifier 100 at injection port 110. The injected pulse is directed along an optical path to a time delay stage 115 and cavity polarizer 117 (e.g., a Brewster's angle polarizing beam splitter). Since the injected pulse has a first polarization state, it is transmitted through the cavity polarizer 117 and the PEPC 120 operating in the "OFF" state. After propagation through the cavity spatial filter (CSF) 130 (e.g., an angularly multiplexed CSF that performs image relaying and beam resizing) and the amplifier unit 140, the amplified pulse is reflected from the first cavity mirror 150, which can be a deformable mirror (DM). The amplifier unit 140 can be implemented as a 20 cm aperture disk amplifier stage. After a second amplification pass through the amplifier unit 140 and the CSF 130, the twice-amplified pulse is incident on the PEPC 120, which has been switched into the "ON" state. As a result, the PEPC 120 rotates the polarization state of the amplified pulse by 90° so that the twice-amplified pulse is reflected by the cavity polarizer 117 and trapped in the cavity by the second cavity mirror 125.

[0023] After multiple amplification passes, for example, six amplification passes, the PEPC 120 is switched back to the "OFF" state and the amplified pulse passes through the cavity polarizer 117 and the infrared diagnostic beam splitter (IR DBS) and exits the multipass amplifier 100 toward the frequency conversion crystal (FCC) and second harmonic generation (SHG) crystal (i.e., a sum frequency generation stage). Thus, the pulse remains trapped in the cavity while the PEPC 120 remains energized at its half-wave voltage, and escapes from the cavity only when the PEPC is switched to the "OFF" state.

[0024] In some embodiments, the round trip time for the multipass amplifier 100 is -110 ns and the multipass amplifier 100 provides a 22 cm diameter beam aperture.

[0025] FIG. 2A is a simplified perspective view of a PEPC according to an embodiment of the present invention. As shown in FIG. 2A, the PEPC 200 includes a set of cell bodies 210. Each of the cell bodies 210 includes two input ports 204 and is attached to a vacuum plenum 202, with the vacuum plenum behind the back cell body not shown. A vacuum pump (not shown) exhausts process gas through the exit ports of the vacuum plenums 202. Light enters and exits the PEPC 200 through windows 209.

[0026] FIG. 2B is a simplified plan view of the PEPC illustrated in FIG. 2A. The plan view illustrated in FIG. 2B shows the electrical connections and other features of the PEPC, including the switch-pulse generator (SPG), plasma-pulse generator (PPG), and the electrooptic crystal 205, which in this embodiment is potassium dihydrogen phosphate, KH2PO4 (KDP).

[0027] In some embodiments, the electro-optic crystal is potted within a glass midplane 220 (e.g., a borofloat glass midplane) using a silicate epoxy. This is sandwiched between two symmetric cell bodies 210 made of aluminum. The cell bodies 210 can be anodized to provide a dielectric barrier that prevents arcing from the plasma. The cell bodies 210 and windows 209 form two plasma chambers 207 (also referred to as vacuum chambers) on either side of the glass midplane 220 between the windows 209. The windows 209 (e.g., circular fused-silica windows) can be mounted on O-rings and held in place by the vacuum force. The inventors have previously demonstrated that the stress induced birefringence in the windows 209 is negligible and permits high switching contrast throughout the clear aperture.

[0028] The electro-optic crystal 205 (i.e., the electro-optic switch crystal) is 270 mm x 270 mm x 10 mm in size, which accommodates a 220 mm diameter (FWHM) circular beam. In some embodiments, Z-cut, undeuterated KDP is utilized, although deuterated KD*P can also be utilized in alternative embodiments. The electro-optic coefficient of KD*P is higher than that of KDP, allowing for a lower switching voltage, and the absorption of KD*P is negligible at 1053 nm, whereas the 1 cm KDP crystal absorbs >5% of the pulse energy on each pass. It should be noted that KD*P has a higher dielectric constant of Er 33= 50 that can lead to excessive capacitance compared to dielectric constant of Er 33= 20 of KDP. The capacitance of the electro-optic crystal 205 is 1.29 nF, although including the additional glass midplane 220, the total capacitance is ~2.5 nF.

[0029] A turbomolecular pump (not shown) forms a vacuum in the two plasma chambers 207, which can also be referred to as plasma discharge chambers, on either side of the electro-optic crystal 205, exhausting each chamber through a corresponding vacuum plenum 202. The cell body 210 is back-filled by a process gas, for example, helium or helium / oxygen, injected through input ports 204 with pressure regulated by mass-flow controllers (not shown). Referring to FIG. 2B, the plasma electrical current is illustrated by current / p. Graphite electrodes are incorporated at either end of the plasma chambers. In some embodiments, there are four button-type anodes for each plasma chamber 207 and thecathodes are planar magnetrons. The plasma present in the plasma chamber is exhausted through vacuum plenum 202 in fluid communication with each of the plasma chambers 207.

[0030] As described more fully in relation to FIG. 3, the plasma is confined to the plasma chambers 207 by plasma isolation structures (implemented in some embodiments as sintered steel filters) that force recombination of electrons and ions near the surfaces of the plasma isolation structures, which are made from porous material. In a particular embodiment, a single 1 / 16 inch thick sintered steel plate available from Pall Corporation of Port Washington, NY, was machined and positioned at the entrance of the vacuum plenum 202. In another embodiment, in order to further prevent leakage of plasma into the vacuum plenum 202 and arcing to the grounded vacuum lines during the switch pulse, a second plasma isolation structure (e.g., a second 1 / 16 inch thick sintered steel plate) was inserted near the exit of the vacuum plenum 202. Plasma isolation structures with different thicknesses can also be used. Although electrically conductive plasma isolation structures in the form of sintered steel plates are used in some embodiments, the plasma isolation structure does not have to be electrically conductive and porous electrical insulators can be utilized as well. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

[0031] The use of the plasma isolation structures not only substantially reduces the plasma leakage into the vacuum plenums, but also reduces the vacuum conductance, enabling the plasma chambers 207 to be operated at an internal pressure ranging from -100 mTorr to -300 mTorr. Using embodiments of the present invention, problems resulting from impurities are reduced or eliminated and, since the turbo pump sees a much lower operating pressure, the turbo pump is not noticeably loaded during servo operation. As an example, the vacuum conductance barrier provided by the plasma isolation structures enables plasma chamber pressures in the range of -100 mTorr while the pressure near the turbo pump is in the range of single or tens of mTorr. Thus, the plasma isolation structures enable embodiments of the present invention to operate at higher plasma chamber pressures than conventional systems, which can utilize serpentine vacuum plenum architectures during operation at lower plasma chamber pressures.

[0032] Referring to FIG. 2B, the PEPC can be operated using a two-step method that utilizes separate plasma and switch pulsers (i.e., separate PPG and SPG), in contrast to single pulse operation that combines plasma generation and electro-optic switching in a single pulse. A low-density plasma is initiated by a starter anode rod in close proximity to thecathode and sustained with a low-current simmer pulse from the two PPGs. This is followed by an ~10 ps main plasma pulse to generate a sufficient plasma density to form high- conductivity electrodes. An 18-kV switch pulse applied between the plasma electrodes produces the required electric field across the electro-optic crystal 205 to impart a half-wave retardance to a 1053 nm beam.

[0033] In some embodiments, the distance between the electrodes and the electro-optic crystal 205 was selected in order to reduce or minimize heating of the electro-optic crystal 205. In the longitudinal direction, parallel to the optical axis, the width of the plasma channel was maintained at levels in the range of 5.5 cm. The use of this width maintains key bulk plasma parameters such as the electron temperature and the electron velocity, which are sensitive to the narrow dimension of the plasma volume.

[0034] In some implementations, the electrically insulating vacuum plenums 202 were fabricated using an acetal homopolymer (i.e., polyoxymethylene (POM-H), also referred to as Delrin). POM-H is a high-performance acetal homopolymer resin (i.e., a highly-crystalline engineered thermoplastic) with several desirable physical and mechanical properties. For example, acetal homopolymers are widely regarded for their durability, stiffness, and exceptional dimensional stability. However, the inventors determined that acetal homopolymers were characterized by an undesirable vacuum leak rate, which the inventors determined was a result of acetal homopolymers containing a low-density center (also known as "center line porosity") that results in vacuum leakage. This center line porosity, which without limiting embodiments of the present invention, the inventors believe is an artifact of the extrusion process used in manufacturing the acetal homopolymer, was particularly present in the large cross-sections utilized to fabricate the vacuum plenums 202. As an example, using vacuum plenums made of acetal homopolymers, the baseline pressure achieved in the plasma chambers was higher than 100 pTorr, which was not suitable because the resulting high concentration of impurities led to poor conductivity of the plasma electrodes.

[0035] Thus, some embodiments of the present invention utilize an acetal copolymer for the fabrication (i.e., the machining) of the vacuum plenums 202 since acetal copolymers offer consistent properties throughout the shape, including the physical and mechanical properties discussed above including being a dielectric insulator, and are free of center line porosity. Thus, the use of a material free of center line porosity enabled the inventors to solve the vacuum leak problem associated with POM-H via the use of an acetal copolymer (e.g.,Acetron ® GP) for the fabrication of the vacuum plenums 202 while maintaining the mechanical and electrical properties provided by acetal homopolymers. As discussed herein, baseline pressures of less than 100 pTorr, including single digit pTorr baseline pressures (i.e., baseline pressures ranging from 1 pTorr to 10 pTorr) were achieved using vacuum plenums made of acetal copolymers.

[0036] Referring to FIG. 2B, the seam corresponding to the low-density center (i.e., the "center line porosity") in acetal homopolymers is illustrated by plane 203 that extends into the plane of the figures and passes through the center of the vacuum plenums 202 parallel to the optical axis and perpendicular to the glass midplane 220.

[0037] FIG. 2C is a simplified cross-sectional end view of the PEPC illustrated in FIG. 2A. The cross-section used for FIG. 2C (i.e., the plane of the figure) is the plane 203 illustrated in FIG. 2B that passes through the center of the vacuum plenum 202 perpendicular to the glass midplane 220. As shown in FIG. 2C, glass midplane 220 is sandwiched between two symmetric cell bodies 210 made of aluminum. The cell bodies 210 form two plasma chambers 207 on either side of the glass midplane 220. During operation, plasma is created in plasma chambers 207 and flows into the plane of the figure toward vacuum plenums 202.

[0038] Each of the vacuum plenums 202 include a set of plasma isolation structures illustrated by proximal plasma isolation structure 310 and distal plasma isolation structure 320 illustrated in and discussed more fully in relation to FIG. 3. The use of the proximal plasma isolation structure 310 positioned near the entrance of the vacuum plenum 202 and the distal plasma isolation structure 320 positioned near the exit of the vacuum plenum 202 produces a decrease in the vacuum conductance and a substantial reduction in the plasma leakage through the vacuum plenums to the vacuum pump in fluid communication with vacuum port 330.

[0039] FIG. 3 is a simplified cross-sectional perspective view of a vacuum plenum according to an embodiment of the present invention. The cross-section used for FIG. 3 is the plane 203 illustrated in FIG. 2B that passes through the center of the vacuum plenum 202 perpendicular to the midplane.

[0040] As shown in FIG. 3, the vacuum plenum 202 that is utilized for the PEPC is fabricated from a nonconductive (e.g., polymer) material that enables the vacuum plenum to preserve the vacuum path and provide electrical isolation. As discussed above, a vacuum plenum may be made of an acetal copolymer that is free of center line porosity in order toachieve lower baseline vacuum pressures than that provided by conventional PEPC architectures. Additionally, as described more fully in relation to FIG. 3, acetal copolymers provide mechanical strength that enables machining to tight tolerances, which enabled the accurate mounting of plasma isolation structures.

[0041] Referring to FIG. 3, vacuum plenum 202 includes two plasma isolation structures, proximal plasma isolation structure 310 that is mounted proximal to flange 305 and distal plasma isolation structure 320 that is mounted distal to flange 305. Although FIG. 3 illustrates the use of two plasma isolation structures, other embodiments can utilize one plasma isolation structure or more than two plasma isolation structures. Thus, the use of one or more plasma isolation structures inside the vacuum plenum is included within the scope of the present invention. Proximal plasma isolation structure 310 is mounted proximal to a first vacuum chamber (e.g., a plasma chamber 207) and distal plasma isolation structure 320 is mounted distal from the first vacuum chamber. Similarly, in the other vacuum plenum, a similar set of plasma isolation structures are utilized. Thus, referring to FIGS. 2A - 2C, the first vacuum plenum can include a first proximal plasma isolation structure and a first distal plasma isolation structure and the second vacuum plenum can include a second proximal plasma isolation structure and a second distal plasma isolation structure. Retaining members 322 can be utilized to mount either or both of proximal plasma isolation structure 310 and / or distal plasma isolation structure 320. Additionally, the first proximal plasma isolation structure 310 is parallel to the first distal plasma isolation structure 320 in this embodiment, although this is not required.

[0042] Referring to FIG. 3 while referring back to FIGS. 2 A - 2C, it is evident that the proximal plasma isolation structure 310 and the distal plasma isolation structure 320 are parallel to the optical windows 209 as well as being parallel to the glass midplane 220 and electro-optic crystal 205. As discussed above, the inventors have determined that acetal copolymers enable precise machining of the vacuum plenum, thereby resulting in accurate placement and mounting of the plasma isolation structures in the vacuum plenum.

[0043] As process gas flows through the plasma isolation structures, which are porous, free electrons and ions recombine, which prevents components of the plasma from reaching the conductive components of the vacuum system. In an embodiment, sintered steel filters are utilized as the plasma isolation structures and are incorporated into the plastic structure of the vacuum plenum such that process gas is forced through the pores of the sintered steel by theaction of the pumping system. Any free electrons and ions entering the porous plasma isolation structure will, by necessity, come in close proximity to a surface that will promote recombination. Thus, plasma entering the plasma isolation structure (e.g., a sintered steel filter) will be significantly reduced in plasma density, effectively emerging as a neutral gas. The plasma isolation structures provide an additional benefit in that they introduce a reduced vacuum conductance between the plasma chamber 207 and the vacuum pump in fluid communication with the vacuum plenum 202, which allows an operating pressure in the >100 m Torr range to be achieved while gas pressure in the vicinity of the vacuum pump being significantly lower, thus reducing wear of the vacuum pump.

[0044] FIG. 4 is a simplified flowchart illustrating a method of operating a PEPC according to an embodiment of the present invention. The method 400 includes providing a set of vacuum chambers (410). A first vacuum chamber is disposed between a first optical window and an electro-optic material and a second vacuum chamber is disposed between a second optical window and the electro-optic material. The method also includes establishing a baseline vacuum pressure in the set of vacuum chambers less than 10 pTorr (412). The baseline vacuum pressure can range from 1 pTorr to 10 pTorr in some embodiments.

[0045] The method further includes flowing a process gas (e.g., helium and oxygen) into each of the set of vacuum chambers (414) and initiating a plasma including plasma components in each of the set of vacuum chambers (416). The method additionally includes exhausting the plasma in the first vacuum chamber through a first vacuum plenum including one or more first plasma isolation structures (418), exhausting the plasma in the second vacuum chamber through a second vacuum plenum including one or more second plasma isolation structures (420), and recombining the plasma components at the one or more first plasma isolation structures and the one or more second plasma isolation structures (422). The one or more first plasma isolation structures and / or the one or more second plasma isolation structures can be fabricated from sintered steel.

[0046] In a particular embodiment, the one or more first plasma isolation structures include a first proximal plasma isolation structure mounted proximal to the first vacuum chamber and a first distal plasma isolation structure mounted distal from the first vacuum chamber. The one or more second plasma isolation structures include a second proximal plasma isolation structure mounted proximal to the second vacuum chamber and a second distal plasma isolation structure mounted distal from the second vacuum chamber. The first proximalplasma isolation structure can be disposed parallel to the first distal plasma isolation structure and the second proximal plasma isolation structure can be disposed parallel to the second distal plasma isolation structure. The first proximal plasma isolation structure and the first distal plasma isolation structure can be parallel to the first optical window and the second proximal plasma isolation structure and the second distal plasma isolation structure can be parallel to the second optical window.

[0047] The vacuum pressure in the set of vacuum chambers during plasma formation and the exhausting of the plasma can range from 30 mTorr to 500 mTorr, for example, from 100 mTorr to 200 mTorr. The plasma isolation structures enable the downstream vacuum pressure downstream of the one or more first plasma isolation structures to be less than the vacuum pressure in the set of vacuum chambers, for example, a downstream vacuum pressure less than half of the vacuum pressure in the set of vacuum chambers. As an example, the vacuum pressure downstream of the one or more one or more first plasma isolation structures can be less than 100 mTorr.

[0048] In some embodiments, the method also includes placing the plasma electrode Pockels cell in an "OFF" state by applying a first voltage across the electro-optic material for a first predetermined time period, placing the plasma electrode Pockels cell in an "ON" state by applying a second voltage across the electro-optic material for a second predetermined time period, and placing the plasma electrode Pockels cell in the "OFF" state by applying the first voltage across the electro-optic material for the first predetermined time period. The second predetermined time period can be greater than the first predetermined time period, which can be less than 100 ns.

[0049] It should be appreciated that the specific steps illustrated in FIG. 4 provide a particular method of operating a PEPC according to one embodiment. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments of the present disclosure may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in FIG. 4 may include multiple sub-steps that may be performed in various sequences as appropriate to the individual step. Furthermore, additional steps may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.

[0050] FIG. 5 is a simplified timing diagram illustrating operation of a PEPC according to an embodiment of the present invention. In this timing diagram, which plots the strength of the applied electric field (i.e., the magnitude of the switch voltage) in arbitrary units and corresponds to the multipass amplifier illustrated in FIG. 1, the unfolded amplifier cavity is shown with six round-trips along the x-axis and arrival times of the pulse at the PEPC indicated by vertical dashed lines. An approximation of the switch pulse, which places the PEPC in the "OFF" state for the duration of the laser pulse for both the first and 12thpasses and in the "ON" state for the intermediate passes, is shown by curve 510.

[0051] As illustrated by the optical switching performance shown in FIG. 5 in conjunction with the multipass amplifier 100 shown in FIG. 1, the total propagation time from the PEPC 120 to the first cavity mirror 150 (e.g., the deformable mirror) and back to the PEPC 120 again will be -100 ns. The PEPC is fully off when the leading edge of the laser pulse arrives and remains de-energized for the duration of the pulse until the tail end of the pulse has exited. Between this time and the return of the leading edge of the pulse after the first roundtrip, the PEPC is fully energized at the half-wave voltage to prevent leakage from the amplifier. Thus, from the 100 ns transit time, the maximum expected duration of the laser pulse is removed. Additionally, allowances for jitter and mistiming further reduce the switching time, with a resulting optical switching time (1% to 99% transmission) of less than 70 ns being implemented by embodiments of the present invention.

[0052] In addition to meeting switching time and switch-pulse duration performance metrics for the PEPC, embodiments of the present invention meet other performance metrics. The contrast, or extinction ratio, of the PEPC is sufficient to not cause excessive passive loss or spatial modulation of the beam through the six round-trips of the amplifier. The inventors have determined that a contrast of 100: 1 was sufficient, with a contrast as low as 50: 1 acceptable locally in the clear aperture. A list of system performance metrics is shown in Table 1.Table 1

[0053] The performance of the PEPC described herein was characterized in a polarimeter system adapted to measure both switching dynamics (on a small beam) and spatially resolved contrast over the full clear aperture.

[0054] FIG. 6 is a simplified schematic diagram of a test stand for the PEPC according to an embodiment of the present invention. As illustrated in FIG. 6, the two small secondary mirrors 610 and 612 of the matching telescope systems are retractable so that the PEPC 605 can be illuminated with a sub-aperture beam or the full beam aperture can be illuminated. The switching time configuration using the continuous wave (CW) laser 620 and sub-aperture beam to photodiode 640 and scope 642 is indicated in red. The contrast configuration using pulsed laser 630 to full -aperture beam to camera 650 is indicated in blue.

[0055] The PEPC test stand is a full-aperture polarimeter with the PEPC located between two reflective telescope systems that up-collimate the beam to fill the PEPC aperture and down-collimate and image relay the transmitted beam. Two linear polarizers (e.g., Polarcor polarizers available from Newport Corporation of Irvine, CA) illustrated as pre-polarizer 614 and analyzer 616 are used to condition the input linear polarization state and to analyze the output polarization state.

[0056] Optical switching time measurements were performed with a CW laser (e.g., IPG YLR-10-1053 available from IPG Photonics Corporation of Marlborough, MA) and a subaperture (~1 inch diameter) beam to maximize signal on a fiber-coupled photodiode (Fermionics FD80, ~120-ps FWHM impulse response available from Fermionics OptoTechnology of Simi Valley, CA) at the output. The small secondary mirrors 610 and 612 of both telescopes are retractable, enabling such a test. The analyzer 616 and pre-polarizer 614 are aligned for this test so that the system is in a normally high-transmission state with the CW laser and the transmission drops to near zero when the PEPC is switched to the halfwave voltage.

[0057] FIG. 7A is a plot of transmittance as a function of time for the PEPC according to an embodiment of the present invention. The optical switching time measurements shown inFIG. 7A, were measured with the PEPC in the test stand shown in FIG. 6 at optimum operating conditions. The displayed optical switching times of the leading and trailing edges of the switch pulse are defined as the time from 99% to 1% transmission and vice versa.

[0058] The data illustrated in FIG. 7A was obtained by configuring the oscilloscope to average 16 switch pulse waveforms and then performing a seven-point (2.4 ns) boxcar average in postprocessing to reduce shot noise in the measurement. The photodiode signal before and after the pulse was averaged to obtain a 100% transmission signal level. The optical switching time from 99% to 1% for the leading edge of the switch pulse was measured to be 62 ns, and the switching time from 1% to 99% for the trailing edge was measured to be 53 ns, resulting in the PEPC exceeding the < 70 ns performance metric.

[0059] FIG. 7B is a plot of six round trip passive transmission as a function of arrival time of the pulse according to an embodiment of the present invention. It should be noted that the data shown in FIG. 7B does not include Fresnel or absorption loss. The results shown in FIG. 7B demonstrate another approach for considering the switching speed that is pertinent to the multipass amplifier. The transmission data shown in FIG. 7A, in conjunction with the knowledge of the arrival times of the laser pulse to the PEPC in the multipass amplifier, allow the total passive transmission for six-round trips in the system to be determined by calculating the total product of the transmission values for the first and last passes and (1-7) for the intermediate passes. This can be calculated as a function of the time, relative to t = 0 in FIG. 7A, that the injected pulse arrives at the PEPC. The result shown in FIG. 7B indicates that there is a broad (i.e., > 40 ns) window within which the total transmission is >95% (excluding Fresnel and absorption losses), which exceeds the 30 ns allotted for the pulse duration, jitter, and mistiming in developing the original switching time performance metrics.

[0060] The data shown in FIG. 7A was obtained after optimization of the key operating parameters. In particular, the relative timing of the switch and plasma pulses and the plasma current were found to be important parameters. The dependence of the switching times (1% to 99% transmission) on the peak current supplied by the plasma pulse generator (PPG) is plotted in FIG. 8.

[0061] FIG. 8 is a plot of the 1% to 99% switching time as a function of peak current according to an embodiment of the present invention. FIG. 8 indicates that there is a minimum plasma current that is exceeded in order to satisfy the switching time requirement.This minimum plasma current is well-explained by plasma theory. The density of electrons and ions at the edge of the plasma near the crystal surface is proportional to the plasma current. This edge density exceeding a minimum level (~2 x 1012cm3) will suppress the development of a sheath at the surface of the crystal, which reduces the voltage being applied across the crystal by the sheath potential. Thus, it is expected that a high enough plasma current is used to produce a sufficiently dense plasma in order to exceed the minimum edge density. Some embodiments operate at a PPG current of 1000 A in order to balance the switching speed achieved and potential degradation of the electrodes at higher current density.

[0062] The contrast measurement uses the setup shown in blue in FIG. 6. A ^-switched Nd:YLF laser (Photonics Industries DC50-1053 available from Photonics Industries International, Inc. of Ronkonkoma, NY ) is used to illuminate the full aperture of the PEPC during the switch pulse. A CCD camera captures an image of the transmitted beam through the analyzer, which can be either aligned or crossed relative to the pre-polarizer, depending on the nature of the test being performed. For aligned polarizers, the transmission through the analyzer should be very low and the resulting "dark" images detect any leakage due to low contrast. To increase dynamic range, some attenuation is typically removed from the system for the dark measurements. A set of "bright" images are acquired in the same configuration, but with extra attenuation and with the PEPC switch turned off. The spatially resolved contrast within the PEPC aperture is then calculated simply, where AOD is the total attenuation, in optical density units, removed for the dark-state measurements. In practice, a number of images of each type are averaged to reduce pulse-to-pulse fluctuations in the laser pulse energy.

[0063] FIG. 9A is a plot of spatially resolved switching contrast measured at the optimum half-wave switch voltage according to an embodiment of the present invention. The plot shown in FIG. 9A is a mosaic of three different measurements with the PEPC translated horizontally to measure regions obscured by the secondary mirrors and mounting structures. The resulting contrast, shown in FIG. 9A, significantly exceeded the desired performance metrics, with spatially averaged contrast measured to be 2,800: 1 and the minimum pointwithin the clear aperture being 1440: 1. The contrast exceeded 2000: 1 for >95% in the clear aperture.

[0064] FIG. 9B is a plot of the measured inverse contrast and the predicted curve as a function of switch voltage according to an embodiment of the present invention. The variation of the contrast with switch voltage is plotted in FIG. 9B, along with the theoretically predicted curve with the half-wave voltage, ITt, as a fit parameter. The agreement is very good and confirms that there is a broad (> ± 1000 V) range of switch voltages over which the contrast is high. Therefore, embodiments of the present invention are tolerant to ripple and pulse-to-pulse fluctuations in the switch pulse waveform.

[0065] Various examples of the present disclosure are provided below. As used below, any reference to a series of examples is to be understood as a reference to each of those examples disjunctively (e.g., "Examples 1-4" is to be understood as "Examples 1, 2, 3, or 4").

[0066] Example 1 is a plasma electrode Pockels cell comprising: a cathode; an anode; a set of optical windows disposed between the cathode and the anode and defining a set of plasma chambers; an electro-optic crystal disposed between the set of plasma chambers; a set of input ports, each of the set of input ports being in fluid communication with one of the set of plasma chambers; a set of electrically insulating vacuum plenums, each of the set of electrically insulating vacuum plenums being in fluid communication with one of the set of plasma chambers; one or more plasma isolation structures disposed in each of the set of electrically insulating vacuum plenums; and a vacuum system in fluid communication with each of the set of electrically insulating vacuum plenums.

[0067] Example 2 is the plasma electrode Pockels cell of example 1 wherein the set of electrically insulating vacuum plenums comprise acetal copolymer.

[0068] Example 3 is the plasma electrode Pockels cell of example(s) 1-2 wherein the set of electrically insulating vacuum plenums comprise a polymer free of center line porosity.

[0069] Example 4 is the plasma electrode Pockels cell of example(s) 1-3 wherein the one or more plasma isolation structures comprise porous sintered steel.

[0070] Example 5 is the plasma electrode Pockels cell of example(s) 1-4 wherein the one or more plasma isolation structures comprise a set of plasma isolation structures disposed parallel to each other.

[0071] Example 6 is the plasma electrode Pockels cell of example(s) 1-5 wherein the one or more plasma isolation structures comprise a set of sintered steel plates, each characterized by a substantially uniform thickness.

[0072] Example 7 is the plasma electrode Pockels cell of example(s) 1-6 wherein the electro-optic crystal is mounted between glass support members.

[0073] Example 8 is the plasma electrode Pockels cell of example(s) 1-7 wherein the electro-optic crystal and the glass support members are located at a midplane between the set of optical windows.

[0074] Example 9 is the plasma electrode Pockels cell of example(s) 1-8 wherein the one or more plasma isolation structures include: a first proximal plasma isolation structure mounted proximal to the set of plasma chambers and a first distal plasma isolation structure mounted distal from the set of plasma chambers; and a second proximal plasma isolation structure mounted proximal to the set of plasma chambers and a second distal plasma isolation structure mounted distal from the set of plasma chambers.

[0075] Example 10 is the plasma electrode Pockels cell of example(s) 1-9 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; and the second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

[0076] Example 11 is the plasma electrode Pockels cell of example(s) 1-10 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the set of optical windows; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the set of optical windows.

[0077] Example 12 is a method of operating a plasma electrode Pockels cell, the method comprising: providing a set of vacuum chambers, wherein a first vacuum chamber is disposed between a first optical window and an electro-optic material and a second vacuum chamber is disposed between a second optical window and the electro-optic material; establishing a baseline vacuum pressure in the set of vacuum chambers less than 10 pTorr; flowing a process gas into each of the set of vacuum chambers; initiating a plasma including plasma components in each of the set of vacuum chambers; exhausting the plasma in the first vacuum chamber through a first vacuum plenum including one or more first plasma isolation structures; exhausting the plasma in the second vacuum chamber through a second vacuumplenum including one or more second plasma isolation structures; and recombining the plasma components at the one or more first plasma isolation structures and the one or more second plasma isolation structures.

[0078] Example 13 is the method of example 12 further comprising: placing the plasma electrode Pockels cell in an "OFF" state by applying a first voltage across the electro-optic material for a first predetermined time period; placing the plasma electrode Pockels cell in an "ON" state by applying a second voltage across the electro-optic material for a second predetermined time period; and placing the plasma electrode Pockels cell in the "OFF" state by applying the first voltage across the electro-optic material for the first predetermined time period.

[0079] Example 14 is the method of example(s) 12-13 wherein the second predetermined time period is greater than the first predetermined time period.

[0080] Example 15 is the method of example(s) 12-14 wherein a transition time between the first predetermined time period and the second predetermined time period is less than 100 ns.

[0081] Example 16 is the method of example(s) 12-15 wherein the baseline vacuum pressure ranges from 1 pTorr to 10 pTorr.

[0082] Example 17 is the method of example(s) 12-16 wherein vacuum pressure in the set of vacuum chambers during the exhausting the plasma ranges from 30 mTorr to 500 mTorr.

[0083] Example 18 is the method of example(s) 12-17 wherein the vacuum pressure ranges from 100 mTorr to 200 mTorr.

[0084] Example 19 is the method of example(s) 12-18 wherein a downstream vacuum pressure downstream of the one or more first plasma isolation structures is less than the vacuum pressure in the set of vacuum chambers.

[0085] Example 20 is the method of example(s) 12-19 wherein the downstream vacuum pressure is less than half of the vacuum pressure in the set of vacuum chambers.

[0086] Example 21 is the method of example(s) 12-20 wherein the process gas comprises helium and oxygen.

[0087] Example 22 is the method of example(s) 12-21 wherein the one or more first plasma isolation structures and the one or more second plasma isolation structures comprise sintered steel.

[0088] Example 23 is the method of example(s) 12-22 wherein: the one or more first plasma isolation structures include a first proximal plasma isolation structure mounted proximal to the first vacuum chamber and a first distal plasma isolation structure mounted distal from the first vacuum chamber; and the one or more second plasma isolation structures include a second proximal plasma isolation structure mounted proximal to the second vacuum chamber and a second distal plasma isolation structure mounted distal from the second vacuum chamber.

[0089] Example 24 is the method of example(s) 12-23 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; and the second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

[0090] Example 25 is the method of example(s) 12-24 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the first optical window; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the second optical window.

[0091] Example 26 is the method of example(s) 12-25 wherein a pressure downstream of the one or more first plasma isolation structures is less than 100 mTorr.

[0092] Example 27 is a multipass optical amplifier comprising: an injection port operable to receive an input pulse having a first polarization state and to direct the input pulse along an optical path; a cavity polarizer disposed along the optical path, wherein the cavity polarizer is operable to transmit the input pulse having the first polarization state and reflect an amplified pulse having a second polarization state orthogonal to the first polarization state; a plasma electrode Pockels cell (PEPC) disposed along the optical path, wherein the PEPC includes: a cathode; an anode; a set of optical windows disposed between the cathode and the anode and defining a set of plasma chambers; an electro-optic crystal disposed between the set of plasma chambers; a set of input ports, each of the set of input ports being in fluid communication with one of the set of plasma chambers; a set of electrically insulating vacuum plenums, each of the set of electrically insulating vacuum plenums being in fluid communication with one of the set of plasma chambers; one or more plasma isolation structures disposed in each of the set of electrically insulating vacuum plenums; and avacuum system in fluid communication with each of the set of electrically insulating vacuum plenums; a cavity spatial filter optically coupled to the PEPC; an amplifier unit optically coupled to the cavity spatial filter; and a first cavity mirror optically coupled to the amplifier unit; and a second cavity mirror optically coupled to the PEPC.

[0093] Example 28 is the multipass optical amplifier of example 27 wherein the set of electrically insulating vacuum plenums comprise acetal copolymer.

[0094] Example 29 is the multipass optical amplifier of example(s) 27-28 wherein the set of electrically insulating vacuum plenums comprise a polymer free of center line porosity.

[0095] Example 30 is the multipass optical amplifier of example(s) 27-29 wherein the one or more plasma isolation structures comprise porous sintered steel.

[0096] Example 31 is the multipass optical amplifier of example(s) 27-30 wherein the one or more plasma isolation structures comprise a set of plasma isolation structures disposed parallel to each other.

[0097] Example 32 is the multipass optical amplifier of example(s) 27-31 wherein the one or more plasma isolation structures comprise a set of sintered steel plates, each characterized by a substantially uniform thickness.

[0098] Example 33 is the multipass optical amplifier of example(s) 27-32 wherein the electro-optic crystal is mounted between glass support members.

[0099] Example 34 is the multipass optical amplifier of example(s) 27-33 wherein the electro-optic crystal and the glass support members are located at a midplane between the set of optical windows.

[0100] Example 35 is the multipass optical amplifier of example(s) 27-34 wherein the one or more plasma isolation structures include: a first proximal plasma isolation structure mounted proximal to the set of plasma chambers and a first distal plasma isolation structure mounted distal from the set of plasma chambers; and a second proximal plasma isolation structure mounted proximal to the set of plasma chambers and a second distal plasma isolation structure mounted distal from the set of plasma chambers.

[0101] Example 36 is the multipass optical amplifier of example(s) 27-35 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; andthe second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

[0102] Example 37 is the multipass optical amplifier of example(s) 27-36 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the set of optical windows; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the set of optical windows.

[0103] Example 38 is the multipass optical amplifier of example(s) 27-37 wherein the second cavity mirror comprises a deformable mirror.

[0104] Example 39 is the multipass optical amplifier of example(s) 27-38 wherein the first cavity mirror comprises a deformable mirror.

[0105] It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A plasma electrode Pockels cell comprising: a cathode; an anode; a set of optical windows disposed between the cathode and the anode and defining a set of plasma chambers; an electro-optic crystal disposed between the set of plasma chambers; a set of input ports, each of the set of input ports being in fluid communication with one of the set of plasma chambers; a set of electrically insulating vacuum plenums, each of the set of electrically insulating vacuum plenums being in fluid communication with one of the set of plasma chambers; one or more plasma isolation structures disposed in each of the set of electrically insulating vacuum plenums; and a vacuum system in fluid communication with each of the set of electrically insulating vacuum plenums.

2. The plasma electrode Pockels cell of claim 1 wherein the set of electrically insulating vacuum plenums comprise acetal copolymer.

3. The plasma electrode Pockels cell of claim 1 wherein the set of electrically insulating vacuum plenums comprise a polymer free of center line porosity.

4. The plasma electrode Pockels cell of claim 1 wherein the one or more plasma isolation structures comprise porous sintered steel.

5. The plasma electrode Pockels cell of claim 1 wherein the one or more plasma isolation structures comprise a set of plasma isolation structures disposed parallel to each other.

6. The plasma electrode Pockels cell of claim 1 wherein the one or more plasma isolation structures comprise a set of sintered steel plates, each characterized by a substantially uniform thickness.

7. The plasma electrode Pockels cell of claim 1 wherein the electro-optic crystal is mounted between glass support members.

8. The plasma electrode Pockels cell of claim 7 wherein the electro-optic crystal and the glass support members are located at a midplane between the set of optical windows.

9. The plasma electrode Pockels cell of claim 1 wherein the one or more plasma isolation structures include: a first proximal plasma isolation structure mounted proximal to the set of plasma chambers and a first distal plasma isolation structure mounted distal from the set of plasma chambers; and a second proximal plasma isolation structure mounted proximal to the set of plasma chambers and a second distal plasma isolation structure mounted distal from the set of plasma chambers.

10. The plasma electrode Pockels cell of claim 9 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; and the second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

11. The plasma electrode Pockels cell of claim 9 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the set of optical windows; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the set of optical windows.

12. A method of operating a plasma electrode Pockels cell, the method comprising: providing a set of vacuum chambers, wherein a first vacuum chamber is disposed between a first optical window and an electro-optic material and a second vacuum chamber is disposed between a second optical window and the electro-optic material; establishing a baseline vacuum pressure in the set of vacuum chambers less than 10 pTorr;flowing a process gas into each of the set of vacuum chambers; initiating a plasma including plasma components in each of the set of vacuum chambers; exhausting the plasma in the first vacuum chamber through a first vacuum plenum including one or more first plasma isolation structures; exhausting the plasma in the second vacuum chamber through a second vacuum plenum including one or more second plasma isolation structures; and recombining the plasma components at the one or more first plasma isolation structures and the one or more second plasma isolation structures.

13. The method of claim 12 further comprising: placing the plasma electrode Pockels cell in an "OFF" state by applying a first voltage across the electro-optic material for a first predetermined time period; placing the plasma electrode Pockels cell in an "ON" state by applying a second voltage across the electro-optic material for a second predetermined time period; and placing the plasma electrode Pockels cell in the "OFF" state by applying the first voltage across the electro-optic material for the first predetermined time period.

14. The method of claim 13 wherein the second predetermined time period is greater than the first predetermined time period.

15. The method of claim 13 wherein a transition time between the first predetermined time period and the second predetermined time period is less than 100 ns.

16. The method of claim 12 wherein the baseline vacuum pressure ranges from 1 pTorr to 10 pTorr.

17. The method of claim 12 wherein vacuum pressure in the set of vacuum chambers during the exhausting the plasma ranges from 30 mTorr to 500 mTorr.

18. The method of claim 17 wherein the vacuum pressure ranges from 100 mTorr to 200 mTorr.

19. The method of claim 17 wherein a downstream vacuum pressure downstream of the one or more first plasma isolation structures is less than the vacuum pressure in the set of vacuum chambers.

20. The method of claim 19 wherein the downstream vacuum pressure is less than half of the vacuum pressure in the set of vacuum chambers.

21. The method of claim 12 wherein the process gas comprises helium and oxygen.

22. The method of claim 12 wherein the one or more first plasma isolation structures and the one or more second plasma isolation structures comprise sintered steel.

23. The method of claim 12 wherein: the one or more first plasma isolation structures include a first proximal plasma isolation structure mounted proximal to the first vacuum chamber and a first distal plasma isolation structure mounted distal from the first vacuum chamber; and the one or more second plasma isolation structures include a second proximal plasma isolation structure mounted proximal to the second vacuum chamber and a second distal plasma isolation structure mounted distal from the second vacuum chamber.

24. The method of claim 23 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; and the second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

25. The method of claim 23 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the first optical window; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the second optical window.

26. The method of claim 12 wherein a pressure downstream of the one or more first plasma isolation structures is less than 100 mTorr.

27. A multipass optical amplifier comprising: an injection port operable to receive an input pulse having a first polarization state and to direct the input pulse along an optical path;a cavity polarizer disposed along the optical path, wherein the cavity polarizer is operable to transmit the input pulse having the first polarization state and reflect an amplified pulse having a second polarization state orthogonal to the first polarization state; a plasma electrode Pockels cell (PEPC) disposed along the optical path, wherein the PEPC includes: a cathode; an anode; a set of optical windows disposed between the cathode and the anode and defining a set of plasma chambers; an electro-optic crystal disposed between the set of plasma chambers; a set of input ports, each of the set of input ports being in fluid communication with one of the set of plasma chambers; a set of electrically insulating vacuum plenums, each of the set of electrically insulating vacuum plenums being in fluid communication with one of the set of plasma chambers; one or more plasma isolation structures disposed in each of the set of electrically insulating vacuum plenums; and a vacuum system in fluid communication with each of the set of electrically insulating vacuum plenums; a cavity spatial filter optically coupled to the PEPC; an amplifier unit optically coupled to the cavity spatial filter; and a first cavity mirror optically coupled to the amplifier unit; and a second cavity mirror optically coupled to the PEPC.

28. The multipass optical amplifier of claim 27 wherein the set of electrically insulating vacuum plenums comprise acetal copolymer.

29. The multipass optical amplifier of claim 27 wherein the set of electrically insulating vacuum plenums comprise a polymer free of center line porosity.

30. The multipass optical amplifier of claim 27 wherein the one or more plasma isolation structures comprise porous sintered steel.

31. The multipass optical amplifier of claim 27 wherein the one or more plasma isolation structures comprise a set of plasma isolation structures disposed parallel to each other.

32. The multipass optical amplifier of claim 27 wherein the one or more plasma isolation structures comprise a set of sintered steel plates, each characterized by a substantially uniform thickness.

33. The multipass optical amplifier of claim 27 wherein the electro-optic crystal is mounted between glass support members.

34. The multipass optical amplifier of claim 33 wherein the electro-optic crystal and the glass support members are located at a midplane between the set of optical windows.

35. The multipass optical amplifier of claim 27 wherein the one or more plasma isolation structures include: a first proximal plasma isolation structure mounted proximal to the set of plasma chambers and a first distal plasma isolation structure mounted distal from the set of plasma chambers; and a second proximal plasma isolation structure mounted proximal to the set of plasma chambers and a second distal plasma isolation structure mounted distal from the set of plasma chambers.

36. The multipass optical amplifier of claim 35 wherein: the first proximal plasma isolation structure is parallel to the first distal plasma isolation structure; and the second proximal plasma isolation structure is parallel to the second distal plasma isolation structure.

37. The multipass optical amplifier of claim 35 wherein: the first proximal plasma isolation structure and the first distal plasma isolation structure are parallel to the set of optical windows; and the second proximal plasma isolation structure and the second distal plasma isolation structure are parallel to the set of optical windows.

38. The multipass optical amplifier of claim 27 wherein the second cavity mirror comprises a deformable mirror.

39. The multipass optical amplifier of claim 27 wherein the first cavity mirror comprises a deformable mirror.

Images