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We have developed preliminary conceptual laser system designs for the Laser ICF (Inertial Confinement Fusion) Fission Energy (LIFE) application. Our approach leverages experience in high-energy Nd:...

A high average power diode pumped solid state laser is used to pump large aperture Ti:sapphire enabling high average power chirped pulse amplification. After compression, over a petawatt of peak power will be used to generate fusion ions and neutrons for materials testing of first wall and final optics candidates.

Hundred-joule, kilowatt-class lasers based on diode-pumped solid-state technologies, are being developed worldwide for laser-plasma interactions and as prototypes for fusion energy drivers. The goal of the Mercury Laser Project is to develop key technologies within an architectural framework that demonstrates basic building blocks for scaling to larger multi-kilojoule systems for inertial fusion energy (IFE) applications. Mercury has requirements that include: scalability to IFE beamlines, 10 Hz repetition rate, high efficiency, and 10 9 shot reliability. The Mercury laser has operated continuously for several hours at 55 J and 10 Hz with fourteen 4 x 6 cm 2 ytterbium doped strontium fluoroapatite amplifier slabs pumped by eight 100 kW diode arrays. A portion of the output 1047 nm was converted to 523 nm at 160 W average power with 73% conversion efficiency using yttrium calcium oxy-borate (YCOB).

We report on the operation of the Mercury laser with fourteen 4 × 6 cm 2 Yb:S-FAP amplifier slabs pumped by eight 100 kW peak power diode arrays. The system was continuously run at 55 J and 10 Hz for several hours, (2 × 10 5 cumulative shots) with over 80% of the energy in a 6 times diffraction limited spot at 1.047 μm. Improved optical quality was achieved in Yb:S-FAP amplifiers with magneto-rheological finishing, a deterministic polishing method. In addition, average power frequency conversion employing YCOB was demonstrated at 50% conversion efficiency or 22.6 J at 10 Hz.

Yttrium calcium oxyborate YCa 4 O(BO 3 ) 3 (YCOB) is a novel non-linear optical crystal possessing good thermal, mechanical and non-linear optical properties. Large-aperture YCOB crystals with 75 mm diameter were grown for high-average power frequency conversion on the mercury laser system. The growth morphology (included facet and spiral growth), cracking and inclusions in the as-grown crystal boule were discussed as the critical problem for large-aperture YCOB crystal growth. This can be minimized through modification of the growth program, including pulling rate, separation procedure, and cooling program. High-average power frequency conversion of the mercury laser using YCOB has been demonstrated, and experimental validation of YCOB material yields 50% conversion at 10 Hz has been achieved.

Operation of the Mercury laser with two amplifiers has yielded 30 Joules at 1 Hz and 12 Joules at 10 Hz with over 8x10{sup 4} shots on the system. Static distortions in the Yb:S-FAP amplifiers were corrected by a magneto-rheological finishing technique.

We have begun building the Mercury laser system as the first in a series of new generation diode-pumped solid-state lasers for inertial fusion research. Mercury will integrate three key technologies: diodes, crystals and gas cooling, within a unique laser architecture that is scalable to kilojoules and megajoule energy levels for fusion energy applications. The primary near-term performance goals include 10% electrical efficiencies at 10 Hz and 100 J with a 2–10 ns pulse length at 1.047 μ m wavelength. When completed, Mercury will allow rep-rated target experiments with multiple chambers for high energy density physics research.

We have begun building the “Mercury” laser system as the first in a series of new generation diode-pumped solid-state lasers for inertial fusion research. Mercury will integrate three key technologies: diodes, crystals, and gas cooling, within a unique laser architecture that is scalable to kilojoule and megajoule energy levels for fusion energy applications. The primary near-term performance goals include 10% electrical efficiencies at 10 Hz and 100J with a 2–10 ns pulse length at 1.047 μm wavelength. When completed, Mercury will allow rep-rated target experiments with multiple chambers for high energy density physics research.

Using a diode-end-pumped technology, a Yb:YAG laser capable of delivering up to 434 W of CW power has been demonstrated. The system incorporates a unique composite rod design which allows for high-average-power operation while simultaneously suppressing parasitic oscillations. Modeling and experimental data to support the quenching of parasitics are discussed. Beam quality measurements for CW operation with several cavity configurations are presented. In particular, beam quality measurements at 340-W CW yielded a beam quality factor of M/sup 2/=21. Predictions of a quasi-three-level model are compared with the experimental data for several output coupler reflectivities. An observed dependence of the cavity mode fill as a function of output coupler reflectivity is discussed. Employing a single acoustooptical switch, the system was Q-switched at 10 kHz and generated output powers up to 280 W with a measured beam quality of M/sup 2/=6.8 at 212 W, With an external dual-KTP crystal configuration, the Q-switched output was frequency converted to 515 nm and produced up to 76 W at 10 kHz in a 30-ns pulse length.

We summarize our efforts in the development of solid-state lasers, including the laser diode arrays, pump light delivery, approaches to thermal management, and novel gain media. Our interests are in developing unique solid-state lasers, including those operating at higher powers, offering less common wavelengths, and having other specialized features. In this paper, we discuss high-power Tm:YAG and Yb:YAG lasers. The gas cooled slab laser concept using Yb:S-FAP, and side-pumped Er:YAG and Cr:ZnSe lasers. We address the optical and thermal physics of these systems and also mention several additional gain media that have the potential of offering unique performance characteristics: Ce:LiSAF, APG-2 laser glass, Dy:LaCl/sub 3/, and Yb:BCBF.

Compact Compton scattering gamma-ray sources offer the potential of studying nuclear photonics with new tools. The optimization of such sources depends on the final application, but generally requires maximizing the spectral density (photons/eV) of the gamma-ray beam while simultaneously reducing the overall bandwidth on target to minimize noise. We have developed an advanced design for one such system, comprising the RF drive, photoinjector, accelerator, and electron-generating and electron-scattering laser systems. This system uses a 120 Hz, 250 pC, 2 ps, 0.35 mm mrad electron beam with 250 MeV maximum energy in an X-band accelerator scattering off a 150 mJ, 10 ps, 532 nm laser to generate 5 × 1010 photons/eV/s/Sr at 0.5 MeV with an overall bandwidth of less than 1%. The source will be able to produce photons up to energies of 2.5 MeV. We also discuss Compton scattering gamma-ray source predictions given by numerical codes.

We present an overview of Compton Scattering gamma-ray and x-ray sources developed at LLNL and their applications to nuclear photonics.

A design for an $X$-band rf photoinjector that was developed jointly by SLAC National Accelerator Laboratory (SLAC) and Lawrence Livermore National Laboratory (LLNL) is presented. The photoinjector is based around a 5.59 cell rf gun that has state-of-the-art features including: elliptical contoured irises; improved mode separation; an optimized initial half cell length; a racetrack input coupler; and coupling that balances pulsed heating with cavity fill time. Radio-frequency and beam dynamics modeling have been done using a combination of codes including PARMELA, HFSS, IMPACT-T, ASTRA, and the ACE3P suite of codes developed at SLAC. The impact of lower gradient operation, magnet misalignment, solenoid multipole errors, beam offset, mode beating, wakefields, and beam line symmetry have been analyzed and are described. Fabrication and testing plans at both LLNL and SLAC are discussed.

The harmonic generating properties of potassium lanthanum nitrate (KLN) and potassium cerium nitrate (KCN) are described. These crystals have much larger nonlinear coefficients than potassium dihydrogen phosphate (KDP) and are nearly noncritically phase matched at room temperature for Type I frequency doubling of 1.064- mu m light, and for Type II doubling of light near 0.95 mu m. Thus, these crystals are useful for generating blue-green light by frequency doubling high-power near-infrared lasers. The crystal growth of KLN and KCN are described by the three component phase diagrams. Crystallographic data for KCN that confirms its structural similarity to KLN are presented. The optical absorption spectra of the two materials are discussed, and the linear refractive indexes are given. >

Laser systems deployed in Inertial Fusion Energy power plants will usher in space qualified laser engineering and materials on a massive scale. Understanding subsystem efficiencies and component Mean Time Between Failure (MTBF) are critical for success.

The crystal structure, refractive indices, and phase-matching conditions for a new nonlinear optical material, L-histidine tetrafluoroborate (HFB), are reported. HFB grows readily, displays favorable mechanical characteristics, and has adequate birefringence to permit phase-matched parametric processes over much of its transparency range (250 nm to 1300 nm). The phase-matching loci and angular sensitivity for second-harmonic generation of 1064-nm light in single crystals of HFB were measured. The effective nonlinearity for HFB is comparable with that of beta-barium borate (~2 pm/V), and its angular sensitivity [delta(Deltak)/deltatheta] is somewhat smaller.

We have designed and built an all-reflective pulse stretcher based on an Offner telescope. It uses cylindrical optics to simplify alignment and reduce aberrations. The stretch is ~1x105 with a bandwidth of 200 nm. The stretcher is to be part of a 10 Hz repetition rate, high-average-power, femtosecond laser. This new design compensates for dispersion in the laser by using gratings of different groove spacing in the stretcher and compressor and a spectral phase corrector plate, made by magneto-rheological finishing, within the stretcher.

Magneto-rheological finishing techniques have been applied to Yb:S-FAP and Ti:sapphire crystals to compensate for submillimeter distortions; improving the transmitted wavefront (10times) and increasing the availability of large aperture parts (>10 cm).

We have commissioned a turnkey 500 mJ, 10 Hz front end laser. The system delivers temporally and spectrally tailored pulses to correct signal distortions within itself or subsequent amplifiers from single longitudinal mode to 250 GHz RF bandwidth.

Magneto-rheological finishing (MRF) imprinting techniques have been applied to Ti:sapphire crystals to compensate for submillimeter distortions, thereby, improving the transmitted wavefront and increasing the availability of large aperture parts.

The Mercury laser will be used to pump a high average power Ti:sapphire chirped pulse amplifier which will produce a compressed peak power >1 petawatt at 10 Hz.

A diode-pumped Nd:YAG laser was frequency doubled to 0.532 microm with an intracavity KTiOPO(4) crystal in a V-cavity arrangement, achieving an output power of 140 W. Acousto-optic Q switching was employed at repetition rates of 10-30 kHz, and the beam quality was assessed at M(2) approximately 50. It was deduced on the basis of our model that the strength of the nonlinear frequency conversion is the main parameter determining the pulse width.

We have grown LaCa(4)O (BO(3))(3) (LaCOB), an isostructural member of GdCa(4)O(BO(3))(3) (GdCOB) family and characterized its nonlinear optical properties. At 1064nm, d(eff) of 0.52+/-0.05 pm /V and an angular sensitivity of 1224+/-184(cm rad)(-1) for type I frequency doubling in LaCOB were determined relative to those of KTiOPO(4) , beta-BaB(2)O(4) , KD(2)PO(4) , LiB(3)O(5) , YCa(4)O(BO(3))(3) (YCOB), and GdCOB. The d(alphabetabeta) and d(gammabetabeta) coefficients of the nonlinear optical tensor for LaCOB, GdCOB, and YCOB were determined to be equivalent within the experimental uncertainty and have values of ?0.26+/-0.04?pm/V and ?1.69+/-0.17?pm /V , respectively. From phase-matching angle measurements at 1064 and 1047nm, we predict that LaCOB is noncritically phase matched at 1042+/-1.5 nm .

Summary form only given. Optical parametric chirped pulse amplification (OPCPA) is an attractive short pulse amplification technology because of its simplicity broad bandwidth and large gain. Pulses from a mode-locked oscillator can be amplified to mJ energies in a single pass of only 2 or 3 nonlinear crystals. Furthermore, OPCPA does not intrinsically produce pre-pulses and does not require electrooptic switching to either select a single pulse from an oscillator pulse train prior to multipass amplification or to inject/eject a pulse from a regenerative amplifier. The major drawback of OPCPA, however, is pump conversion efficiency. The spatio-temporal evolution and relatively long pulse width of commercial Q-switched lasers limits conversion. On the other hand, pump to IR conversion efficiencies of >50% or 90% of the maximum theoretical quantum efficiency have been demonstrated from chirped-pulse, Ti:sapphire amplifiers pumped by commercial Nd:YAG lasers. We present here the first demonstration of a simple hybrid chirped pulse amplification scheme which combines the best of both technologies.

Quasiphase-matched (QPM) optical parametric chirped-pulse amplification (OPCPA) in periodically poled materials such as periodically poled LiNbO3 (PPLN) and periodically poled KTiOPO4 (PPKTP) has been shown to exhibit advantages over the OPCPA in bulk nonlinear crystals [1],[2]. The use of the maximum material nonlinear coefficient results in ultrahigh gain with low pump peak power. Furthermore, the propagation of signal, pump, and idler beams along one of the crystal principal axes eliminates the birefringent walk-off, reduces angular sensitivity, and improves beam quality. Relatively high level of parasitic parametric fluorescence (PF) in QPM OPCPA represents an impediment for simple, single-stage, high-gain amplification of optical pulses from nanojoules to millijoules energies. PF in QPM is increased when compared to PF in critical phase matching in bulk crystals due to broader angular acceptance of the nonlinear conversion process. The PF reduces prepulse contrast and conversion efficiency by competition with the signal pulse for pump pulse energy. Previous experiments with QPM OPCPA have thus resulted in pulse energies limited to tens of microjoules. [3] Optical parametric amplification of a narrowband signal pulse in PPKTP utilizing two pump beams has been demonstrated at a millijoule level [4], but the conversion efficiency has been limited by low energy extraction of pump pulse in the first pass of amplification. Additionally, narrow spectral bandwidth was the result of operation far from signal-idler degeneracy.

This YCOB wavelength converter holds the current world record for an average-power high-pulse-energy laser at 227 W, 10 Hz, and 22.5 J per pulse. YCOB crystals have been scaled by a factor of 27.

We have produced over 500 mJ using a hybrid fiber-based master-oscillator system coupled with a Yb:S-FAP power amplifier. This system is designed with spatial, temporal, and spectral sculpting enabling broadband amplification correctable for gain narrowing.

The Mercury laser project is part of a national inertial fusion energy program in which four driver technologies are being considered including solid-state lasers, krypton fluoride gas lasers, Z-Pinch and heavy ions. Mercury's operational goals of 100 J, 10 Hz, 10% efficiency in a 5 times diffraction limited spot will demonstrate the critical technologies required for scaling the system to the multi-kilojoule level. Five one hour runs were conducted to assess system stability and reliability; energy fluctuations during the 55 J operations showed a 0.6% rms deviation. Current beam quality during average power operation is approximately 10 times diffraction limited. In the future, active wavefront control, and corrector plates for steady state thermal distortions will be implemented to achieve the 5 times diffraction limited spot.

The Titan laser, designed to produce up to 600 J with pulses of 0.4-200 ps, has begun initial target shots. Coupled with a kJ long-pulse beam, Titan will support high-energy-density physics research at LLNL.

We have frequency doubled the Mercury laser using a single plate of yttrium calcium oxyborate (YCOB), producing 225 W (22.5 J, 10 Hz) of 523.5 nm light.

A novel scheme is described that overcomes parametric-fluorescence limitations of quasi-phase-matched, optical-parametric chirped-pulse amplification to produce millijoule pulse energies at 1053 nm. High gain, beam quality, bandwidth, and extreme prepulse contrast are demonstrated.

We report on the design of a novel, high energy (200 J), short pulse (150 fs) laser that is based on hybrid, broadband optical parametric chirped pulse amplification (OPCPA) and mixed silicate and phosphate Nd:glass amplification.

A new high-contrast, high-gain optical parametric chirped-pulse amplifier (OPCPA) architecture is demonstrated in periodically poled KTiOPO4 (PPKTP). This architecture overcomes parametric fluorescence contrast limitations of the OPCPA in periodically poled materials. The scheme is based on two passes of a single relay-imaged pump pulse and a free-propagating signal pulse through a 1.5 mm x 5 mm x 7.5 mm PPKTP crystal. The output energy of 1.2 mJ is generated at a center wavelength of 1053 nm by 24 mJ of pump energy. A prepulse contrast level of3 x 10(7) was measured with10(6) saturated gain in the amplifier. Amplified pulses were compressed to 200 fs. This simple and versatile concept requires only a modest pump energy from a commercial pump laser and represents a possible high-contrast front end for high-energy Nd:glass-based petawatt-class lasers.

We report initial operation of the Mercury laser with seven 4 x 6 cm S-FAP amplifier slabs pumped by four 80 kW diode arrays. The system produced up to 33.5 J single shot, 23.5 J at 5 Hz, and 10 J at 10 Hz for 20 minute runs at 1047 nm. During the initial campaign, more than 2.8 x 104 shots were accumulated on the system. The beam quality of the system was measured to be 2.8 x 6.3 times diffraction limited at 110 W of output, with 96% of the energy in a 5X diffraction limited spot. Static wavefront glass plates were used to correct for the low order distortions in the slabs due to fabrication and thermal loading. Scaling of crystal grown has begun with the first full size slab produced from large diameter growth. Using an energetics optimization code we find the beam aperture is scalable up to 20 x 30 cm and 4.2 kJ.

We have demonstrated a high-gain optical parametric chirped-pulse amplifier for Nd:glass-based short-pulse laser systems based on periodically poled potassium-titanyl-phosphate. Our amplifier produced high single-pass gain, broad bandwidth, excellent beam quality and stability.

We describe an electro-optically Q-switched, diode-pumped Nd:YAG slab laser oscillator operating at an average power of greater than 250 watts. More than 100 watts of frequency doubled light has been demonstrated.

Experimental data that exhibits a continuous-wave, second-harmonic intensity threshold (15 kW/cm2) that causes two-photon nonlinear absorption which leads to time-dependent photochromic damage in periodically poled KTiOPO4 is presented and verified through a thermal dephasing model.

We have performed extensive numerical studies of quasi-phase-matched optical parametric amplification with the aim to improve its nondegenerate spectral bandwidth. Our multi-section fan-out design calculations indicate a 35-fold increase in spectral bandwidth.

L-histidine tetrafluoroborate (HFB) is a new nonlinear optical material, potentially useful for UV to near IR frequency conversion applications. HFB is an example of a semiorganic material, in which a highly nonlinear organic anion is incorporated into an inorganic salt matrix. HFB grows readily from solution, displays favorable mechanical characteristics for nonlinear optical applications, and has adequate birefringence to allow phase matched parametric processes over much of its transparency range (250 nm to 1300 nm). Its crystal structure, refractive indices, and phase matching conditions are reported. The phase matching locus and angular sensitivity for second harmonic generation of 1064 nm light in single crystals of HFB were measured. For 1.064 μm second harmonic generation, the effective non-linearity for HFB is comparable to that of beta barium borate (~ 2 pm/V), while its angular sensitivity [δ(Δk)/δθ] is somewhat smaller.

We have demonstrated a thermally compensated KTiOPO4 (KTP) Q‐switch with a 10 mm × 6 mm clear aperture and high contrast ratio. This device showed excellent resistance to thermal depolarization at average power densities as high as 1 kW/cm2. Capacitive coupling allowed us to operate the Q‐switch for greater than 109 shots with no sign of electrochromic damage.

We have characterized the effective linear electro-optic coefficients of YCa4O(BO3)3 (YCOB) relative to KH2PO4 and KD2PO4 at 632.8 nm. We measured a maximum r(eff) value of 10.8 +/- 1.4 pm/V for YCOB in a transverse electric field configuration for propagation along the X or the alpha dielectric axis, with the electric field applied along the Z or the gamma dielectric axis. We also found effective coefficients of 10.7 +/- 1.0 and 3.4 +/- 0.4 pm/V for YCOB in longitudinal configurations. The remaining values of r(eff) for various transverse applied voltages were found to be less than 3 pm/V. The excellent thermomechanical properties of this crystal, coupled with moderate electro-optic coefficients, make YCOB and its isomorphs potential candidates for use as high-average-power electro-optic switches.

Summary from only given. We have built and tested a scaleable, half-aperture, dual KD/sub 2/PO/sub 4/ (DKDP) crystal Pockels cell, which, in off-line testing, exhibits less than 0.5% depolarization when thermally loaded with a 100 W near-infrared laser. The arrangement uses a pair of DKDP crystals as a thermally compensated Q-switch.

Mechanical and Aeronautical Engineering, University of California, Davis, CA 95616 USA Abstract: Operation of the Mercury laser with one of two amplifiers activated has yielded 31.6 Joules at 0.1 Hz and 20.6 Joules at 10 Hz. Correction of static distortions in the amplifier was accomplished using a conjugate phase optic.

We have generated approximately 100 W of frequency doubled light from the output of an electro‐optically Q‐switched diode‐pumped Nd:YAG slab laser oscillator operating at an average power of 200 W (2.5 kHz repetition rate, 80 mJ/pulse, 30 ns pulsewidth). The Q‐switch was a compensated z‐axis propagation LiNbO3 electro‐optic modulator, and the frequency conversion crystal was a thin slab of KTP. In addition, Q‐switched operation at an average power of approximately 250 W with 26 ns pulsewidths has been demonstrated.

We discuss how solid-state laser technology can serve in the interests of fusion energy beyond the goals of the National Ignition Facility (NIF), which is now being constructed to ignite a deuterium-tritium target to fusion conditions in the laboratory for the first time. We think that advanced solid-state laser technology can offer the repetition-rate and efficiency needed to drive a fusion power plant, in contrast to the single-shot character of NIF. As discussed below, we propose that a gas-cooled, diode-pumped Yb:S-FAP laser can provide new paradigm for fusion laser technology leading into the next century.

We demonstrated a high-pulse energy, femtosecond-pulse source based on optical parametric chirped-pulse amplification. We successfully amplified 1-microm broadband oscillator pulses to 31 mJ and recompressed them to 310-fs pulse duration, at a 10-Hz repetition rate. The gain in our system is 6 x 10(7), achieved by the single passing of only 40 mm of gain material pumped by a commercial Q-switched Nd:YAG laser. This relatively simple system replaces a more complex Ti:sapphire regenerative-amplifier-based chirped-pulse amplification system. Numerous features in design and performance of optical parametric chirped-pulse amplifiers make them a preferred alternative to regenerative amplifiers based on Ti:sapphire in the front end of high-peak-power lasers.

Optical parametric chirped pulse amplification (OPCPA) is a scalable technology for ultrashort pulse amplification. Its major advantages include design simplicity, broad bandwidth, tunability, low B-integral, high contrast, and high beam quality. OPCPA is suitable both for scaling to high peak power as well as high average power. We describe the amplification of stretched 100 fs oscillator pulses in a three-stage OPCPA system pumped by a commercial, single- longitudinal-mode, Q-switched Nd:YAG laser. The stretched pulses were centered around 1054 nm with a FWHm bandwidth of 16.5 nm and had an energy of 0.5nJ. Using our OPCPA system, we obtained an amplified pulse energy of up to 31 mJ at a 10 Hz repetition rate. The overall conversion efficiency from pump to signal is 6%, which is the highest efficiency obtained with a commercial tabletop pump laser to date. The overall conversion efficiency is limited due to the finite temporal overlap of the seed (3 ns) with respect to the duration of the pump (8.5 ns). Within the temporal window of the seed pulse the pump to signal conversion efficiency exceeds 20%. Recompression of the amplified signal was demonstrated to 310 fs, limited by the aberrations initially present in the low energy seed imparted by the pulse stretcher. The maximum gain in our OPCPA system is 6x107, obtained through single passing of 40 mm of beta- barium borate. We present data on the beam quality obtained from our system (M2=1.1). This relatively simple system replaces a significantly more complex Ti:sapphire regenerative amplifier-based CPA system used in the front end of a high energy short pulse laser. Future improvement will include obtaining shorter amplified pulses and higher average power.

Summary form only given. Optical parametric chirped pulse amplification (OPCPA) offers several advantages when compared to regenerative chirped pulse amplification using Ti:sapphire or Cr:LiSAF. These advantages include low cumulative nonlinear phase (B-integral), greater wavelength flexibility, and high gain achieved without the use of gated electro-optic modulators and multipass amplification. High-energy OPCPA systems pumped by large aperture, low repetition rate glass laser systems have produced up to 0.5 J of amplified stretched pulses, subsequently recompressed to 300 fs. However, OPCPA using commercially available Q-switched pump lasers have, to date, only produced 600 /spl mu/J of amplified signal with a pump-to-signal conversion efficiency near 0.3 %. This low efficiency limits the attractiveness of OPCPA to facilities with high energy, shorter pulse pump lasers. We report chirped pulse amplification of broadband 1054 nm pulses to 31 mJ by single passing only 40 mm of gain material pumped by a commercial Q-switched laser, with a pump to signal conversion efficiency of 6%.

Summary form only given. The physical robustness of the GdCOB family of nonlinear crystals has attracted interest in these materials in applications involving high-average power. Large crystal growth of these materials is relatively easy, they readily and quickly accept a high quality optical polish, and are non-hygroscopic. High average power conditions encountered in intracavity frequency conversion makes desirable an intracavity converter crystal that has low angular and temperature sensitivities. We report values of the thermal sensitivity, /spl beta//sub T/=(/spl delta//spl Delta/k//spl delta/T), and angular sensitivity, /spl beta//sub /spl theta//=(/spl delta//spl Delta/k//spl delta//spl theta/), for LBO, GdCOB, and LaCOB as determined from experiment.