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The development of solid state tunable lasers in the ultraviolet region would have a wide range of applications, including atmospheric remote sensing, atmospheric spectroscopy and pollution monitoring. The first work with Ce : LiCAF was published in 1993, with subsequent reports on favorable results with Ce : LiSAF. While the optical quality of Ce : LiSAF is superior, it suffers from solarization. In contrast, Ce : LiCAF shows minimal solarization and higher efficiencies, even with the typically high-scatter materials available. This presentation will summarize the crystal growth and material characterization of a series of colquiriite crystals with various Sr : Ca ratios. Based on these results, in addition to laser measurements, an optimum composition of Ce : LiSr x Ca 1− x AlF 6 will be determined.

We have demonstrated an upconversion-pumped blue laser on the (1)G(4)-(3)H(6) band of Tm:YAG at cryogenic temperatures. Measurements were also made to assess the possibility of room-temperature upconversion-pumped lasers in Tm:YAG on both the (1)G(4) -(3)H(6) and the (1)D(2)-(3)F(4) bands.

A room-temperature Tm:YVO4 laser at 1.94 μm has been demonstrated for the first time to our knowledge. This laser is characterized by a broad bandwidth and a large absorption cross section for the 800-nm pump band. A slope efficiency of 25% was obtained under nonoptimal conditions.

We report the first observation to our knowledge of coherent emission at 473 nm from an intracavity-doubled Nd:YAG microlaser. The d32 coefficient of potassium niobate was used in a 90-deg, temperature-tuned, Type I phase-matching configuration to generate the second harmonic of the 946-nm intracavity field. Output powers in excess of 5 mW at optical conversion efficiencies of approximately 2% have been observed with dye-laser pumping at 588 nm.

Two-wave mixing absorption in a supersonic beam containing I2 has been studied. The results are in agreement with theory for probe intensities comparable with the pump intensity. However, at very low probe-beam intensities, the absorption deviates substantially from the predicted value and becomes the same as that for the pump beam alone. We believe that this behavior is caused by density variations in the molecular beam and suggest that this effect can be developed into a tool for probing optical inhomogeneities on a microscopic scale.

The feasibility of using a severely aberrated pump beam to amplify effectively without distortion a diffraction-limited Raman beam has been studied. In these experiments the XeCl laser served as the pump and H(2) as the Raman medium. Degradation of the amplified Stokes beam quality with increase in the Raman gain was observed and measured.

The laser-heated pedestal growth technique has been used in conjunction with a unique feedstock preparation method to grow small single crystal rods of Nd-doped and Tm-doped YLF. Starting powder materials were purified by hydrofluorination and melted to form a solidified mass from which feed rods were fabricated. Oriented crystal rods of 1–3 mm diameter were grown with good optical quality. Due to the large difference in their segregation coefficient, Tm-doped samples showed uniform dopant distribution along the growth axis while Nd-doped YLF showed increasing Nd concentration with grown length.

Cerium has been doped in both LiCAF and LiSAF. However, each host has some intrinsic problems resulting in scatter and thermal expansion coefficient issues, respectively. In order to optimize the laser host, crystals were grown on various compositions of Ce,Na:LiSr x Ca 1-x AlF 6 . The materials produced were characterized using a variety of methods, including differential thermal analysis, glow-discharge mass spectrometery, electron microprobe, and various microscopic techniques. Samples were fabricated to characterize the absorption and emission properties for each crystal composition. Finally, laser threshold and efficiency were characterized for the various samples. Through an analysis and comparison of these critical aspects, an optimized, commercially-viable crystal can be identified to be incorporated into a tunable, solid-state UV laser system. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. In the case of the selected crystal system, the crystal growth characteristics of the various crystals are very similar. Absorption and emission values for the strontium-rich compositions are greater than those for the calcium-rich compositions. Lasing was achieved in all of the samples with different output coupler transmissions. The Sr/Ca=35/65 composition showed the highest output powers. Taking into consideration all three aspects of this resaerch, there exists an intermediate composition close to Sr/Ca=35/65, that would be an optimized host as a novel UV laser host.

The development of solid state tunable lasers in the ultraviolet region would have a wide range ofapplications, includingatmospheric remote sensing, atmospheric spectroscopy and pollution monitoring. The first work with Ce:LiCAF waspublished in 1993, with subsequent reports on favorable results with Ce:LiSAF. While the optical quality ofCe:LiSAF issuperior, it suffers from solarization. In contrast, Ce:LiCAF shows minima! solarization and higher efficiencies, even withthe typically high-scatter materials available. This presentation will summarize the crystal growth and materialcharacterization ofa series ofcolquiriite crystals with various Sr/Ca ratios. Based on these results, in addition to lasermeasurements, an optimum composition ofCe:LiSrCa1AlF6 will be determined. 1. INTRODUCTION There are two primary private-sector commercial markets for the cerium-doped colquiriites. The first will be as a new add-on component for research scientists who already have fourth harmonic (266 nm) laser systems in their laboratories. Severallaser companies have introduced diode-pumped 266 nm lasers into the marketplace, and there are over 2000 lasers in the fieldwith the capability ofoperating at 266 nm. The second commercial market that would have an interest in a well-developedCe-doped colquiriite laser material is the environmental monitoring industry. There are many chemical species ofinterest inthe UV that could be accessed ifa highly efficient, broadly tunable, all-solid-state system were available. For this market,laser manufacturers anticipate sales ofcomplete units, which would include the 266 nm pump source and the Ce:colquiriiteadd-on component. Through the appropriate selection of an optimized Ce-doped laser host and laser resonator component forfrequency tuning, the Ce:colquiriite crystals could generate output to probe the absorption ofatmospheric pollutants,contaminants, and aerosol species, such as ozone (280-320 nm). Several other species of interest in the UV include 502, 03,toluene, benzene, N0, ClO, and xylene. This market, albeit somewhat smaller than the market for direct harmonicgeneration at a fixed UV wavelength, is expected to grow rapidly in the next decade if sources and crystals become readilyavailable. Additionally, there are several government-based markets for tunable Ce-doped colquinite solid state lasers.Some ofthe non-classified applications include anti-ship missile defense devices, shipboard threat warning systems, short-range urban communication systems in the solar blind region ofthe ultraviolet, and covert communications systems to beutilized during in-flight fueling by Navy and Air Force pilots. There is also a need for a moderate energy source (lO-lOOmJ,10Hz, 280-320 nm) for standoffdetection ofbiological warfare monitoring and detection. Tryptophan, which is an agenttypically used to carry biological agents in the battlefield, has a broad absorption form 280-310 nm. 290 nm sources wouldbe useful for ground-based line-of-sight monitoring ofchemical pollutants from refineries, power plants, and smokestacks.Previous work with the growth ofthe cerium-doped colquiriites resulted in the selection ofa modified Czochralski furnacefor the growth ofthese crystals. Attempts at improving dopant distribution prompted growth runs using Na, Mg2, and Zn2as co-dopants. The use ofNa as a codopant resulted in crystals with the least amount ofcracking, more uniformity in Ce3doping, and a lower tendency for solarization.Cr:LiSr08CaAlF6was first reported as a potential tunable laser in November 1992.' In this report, it was noted that LiSAFexhibits a weaker crystal field strength, resulting in a larger cross section than Cr:LiCAF. The LiCAF host, however, hasmore favorable mechanical properties. The mixed crystal reportedly had spectroscopic and lasmg properties similar toLiSAF and mechanical properties more typical of LiCAF. In the case of cerium doping of the colquiriites, Ce:LiSA.F grows

We report the influence of growth atmosphere and purity of starting material on the uv-visible transmission characteristics of sapphire fibers grown by the laser-heated pedestal growth method. Improved performance in the visible has been achieved by annealing the fibers to remove color center absorption associated with an impurity, likely a transition metal.

Sapphire fibers grown at 20 mm/min in helium, using an improved laser-heated pedestal growth apparatus, have been shown to exhibit very low losses. The laser damage threshold and bending loss of these fibers have been evaluated. The best fiber forms for energy delivery may be a 100-micron diameter fiber with flared ends to increase the power handling capability while retaining the flexibility. Such a fiber has been successfully grown in our laboratory.

upconversion rate it requires a detailed knowledge of the excited state densities. In this study, the Ho ions are selectively excited to 5Ι7 to create a uniform distribution of excited ions and emissions from higher excited states are monitored as a measure of the upconversion processes.

Recent progress in rapid growth of high optical quality laser crystals is reported. Small rods of 1 to 3 mm diameter of singly or multiply doped garnets and fluorides can be grown at low cost for material evaluation and for use in diode pumping.

The 3 um erbium laser has been the subject of severa1 investigations in recent years to improve the laser performance. They ranged from using new host crystals to adding codopant ions in an effort to eliminate the self-terminating behaviour of the (4111/2 -4113/2) lasing transition. Codoped Er:YAG with Nd [1] was not successful in reversing the lifetime ratios while the same codoped system in a YALO host [2] led to lower state lifetime shorter than the upper state, but the latter was significantly quenched. CW operation of this lasing transition was reported in a diode-pumped Er:YLF laser [3] as well as a krypton ion pumped Er:YSGG laser [4]. No codopant was used and a nonlinear quenching mechanism that depopulates the metastable 4113/2 state under high excitation condition is believed to be responsible for the cw operation. Huber et al [4] also found that codoped Er:YSGG with Ho gave better slope efficiency.

A new version of laser heated pedestal growth system is described which is amenable for the rapid growth of single crystal fibers. The system incorporates a Gaussian reflector to reshape the radial intensity profile of the CO2 laser beam. When He is used as the growth atmosphere, high optical quality sapphire fibers can be produced at rates as high as 2 cm/min with this apparatus.

A 2- mu m Tm:YAG laser using a 1-mm diameter laser rod fabricated from material grown by the laser-heated pedestal growth technique has been characterized. Laser performance was found to be essentially identical to that obtained with bulk grown crystals. This demonstrates the usefulness of this technique for solid-state laser material evaluation and for the growth of laser-quality crystals in sizes suitable for laser diode pumping. >

The feasibility of using a multi-MeV He(+)-ion beam to convert the outer portion of a crystal fiber into cladding is demonstrated. When applied to a-axis LiNbO(3) fiber, the resulting structure has been found to show good waveguiding characteristics.

The radiative lifetimes and collisional deactivation rate constants, in argon, of eight Kr(4p5[2P1/2]5p and [2P3/2]5p) levels have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The measured radiative lifetimes are compared with other experimental values and with theoretical calculations. Radiative branching ratios of these excited states also were measured in order to assign the absolute transition probabilities of the Kr(5p,5p′–5s, 5s′) transition array from the radiative lifetimes. In addition to the total deactivation rate constants, product states from two‐body collisions between Kr(5p and 5p′) atoms and ground state argon atoms were identified from the laser‐induced emission spectra, and product formation rate constants were assigned. Two‐body intermultiplet transfer from Kr(4p5[2P1/2]5p) to the Kr(4p5[2P3/2]4d) levels occurs with ease. Intermultiplet transfer from the lowest level in the (4p55p) configuration to the Kr(4p55s and 5s′) manifold...

The radiative lifetimes and collisional deactivation rate constants by argon of four Xe(5p 5[2P3/2]6p), three Xe(5p 5[2P1/2]6p), and three Xe(5p 5[2P3/2]7p) levels, hereafter referred to as Xe(6p), Xe(6p′), and Xe(7p) states, have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The deactivation rate constants of the 6p levels are in the (0.5–5)×10−11 cm3 s−1 range; however, the rate constants for the 6p′ and 7p levels are much higher with values of (15–40×10−11 cm3 s−1. Product states resulting from two‐body collisions between the laser excited Xe(6p, 6p′, and 7p) atoms and ground state argon atoms were identified from the product emission spectra. In addition to intramultiplet relaxation, considerable intermultiplet transfer to the 6s′ levels seems to occur for the Xe(6p) states. Both intramultiplet relaxation and intermultiplet transfer (to the 6d, 5d, and 7s manifolds) are important for the Xe(6p′) and Xe(7p) states. Radiative branching ratios for...

ArF (B–X) emission at 193 nm has been studied as a function of pressure in Ar/F2, Ar/NF3, Ne/Ar/F2, and Ne/Ar/NF3 mixtures under long pulse electron‐beam excitation. Fluorescence yield, formation yield, as well as apparent quenching rate constants of the ArF* (B) state by Ne, Ar, F2, and NF3 have been measured. While the ArF* formation yield is about the same as per neon or argon excitation produced, highest fluorescence yield is obtained from a Ne/Ar/F2 mixture. Using Ne as the main diluent gas prevents the rapid conversion of ArF* to Ar2F* and Ne itself is a slower quencher of ArF* than Ar.

The radiative lifetimes and two‐body deactivation rate constants of the Ar(3p54p and 4p′) levels have been measured by a time‐resolved laser‐induced fluorescence technique in a flowing afterglow apparatus. The flowing afterglow produced the Ar(3p54s,3P2) metastable atoms, which subsequently were pumped by the pulsed dye laser. The measured radiative lifetimes are in excellent agreement with the calculated transition probabilities based upon intermediate‐coupling theory. Radiative branching ratios of these states also were measured in order to assign the transition probabilities and the absorption oscillator strengths of the transitions between the 4s and 4p levels. The two‐body deactivation rate constants range from 1×10−10 to 2×10−11 cm3 atom−1 sec−1. Specific product states from the two‐body collisions between Ar(4p and 4p′) atoms and Ar were identified from the laser‐induced emission spectra and rate constants for individual product states were assigned for each level. Our results show that two‐body co...

The dissociative excitation of HgBr2 by rare‐gas metastable atoms and N2(A3J+u) has been studied in a flowing afterglow apparatus. Reaction of HgBr2 with the lighter rare gas (He, Ne, and Ar) metastable atoms gave strong Hg* line emissions. Intense HgBr (B2J+→X2J+) emission (300–513 nm) from Xe(3P2) and N2(A) reactions was observed. The rate constants for HgBr* (B) formation from HgBr2 excitation by Xe(3P2) and N2(A) were determined as (5.31.5) ×10−10 cm3 sec−1 and ⩽1×10−10 cm3 sec−1 at 350 °K, respectively. Also, the formation rate constant for HgBr* (C) from HgBr2+Xe(3P2) was determined to be (1.10.3) ×10−10 cm3 sec−1.

Formation of XeCl* from the Xe+(3P2)+HCl is slightly endothermic. In this work laser excitation of HCl (v = 1) in the presence of Xe(3P2) produced in a flowing afterglow apparatus allows direct observation of XeCl* fluorescence from the Xe(3P2)+HCl(v = 1) reaction. The formation rate constant is determined to have a lower limit of 2×10−10 cm3 s−1.

The radiative decay and collisional deactivation of eight of the ten neutral atomic neon (2p 5 3p) levels have been studied. Neon metastable atoms were generated by a hollow‐cathode discharge in a flowing afterglow apparatus and were optically pumped by a pulsed tunable dye laser to selected p states; the decay rates then were determined as a function of neon pressure from 1–8 Torr by analyzing the decay of spontaneous emission from the excited level. The radiative lifetimes of these eight p states have been measured with an uncertainty of ±3%. These lifetimes were combined with the radiative branching ratios from a given p level to assign absolute transition probabilities for the Ne(3p–3s) transitions. Two‐body deactivation of the Ne(3p) states by collisions with ground state neon atoms have rate constants in the range of 1–5×10−11 cm3 atom−1 sec−1. Intramultiplet relaxation is the dominant quenching mechanism for the p3, p4, p5, p6, p7, and p8 levels. However, for p9 intermultiplet and intramultiplet re...

Transient absorption experiments in pure and mixed rare gases were performed at the XeF laser wavelength using a broadband probe technique. The major absorbing species in this region are identified. There is a strong broadband absorption in electron‐beam‐excited argon which is due to Ar+2. In neon plasmas the broadband absorption is much weaker. However, there are a number of strong line absorptions due to Ne(3s‐4p) transitions, one of which coincides with the 351‐nm emission band of the XeF laser. Addition of xenon reduces Ne* absorption. The amount of xenon used is limited by the formation of Xe+2, which is also a strong absorber in the 350‐nm region.

Formation and quenching processes of the XeCl (B) state have been investigated. Mixtures of Ne/Xe/HCl have been irradiated by an electron beam of 0.6 μsec duration. The results indicate that the formation efficiency of the XeCl (B) and (C) states are 143%and 31%, respectively. If these states are closely coupled, the ultimate efficiency of the XeCl (B→X) laser is 174%. Two‐body quenching by neon is the major loss process. At a pumping current of 7 A/cm2, electron mixing of the B and C states is negligible; however, electron quenching may be present, and at most a 20% effect.

The key to an effective laser material evaluation program is a ready supply of crystals at a reasonable cost. For most studies a crystal rod size of 1-mm diameter and 10-mm length is sufficient. More important for material optimization is the number of crystals with different dopant concentrations. Bulk growth techniques would not be appropriate for this task. This paper presents the laser-heated pedestal growth technique as a fast and cost-effective way to grow small laser crystals. Rare earth doped garnets of good crystal quality are now routinely grown at our facility. Lifetime measurements showed good agreement with those of bulk crystals. Tm:YAG is one of the dopant/host combinations studied as a function of dopant concentration. At high thulium concentration, excitation in metastable 3F4 ions can migrate over a large number of sites in the lattice and be quenched by impurities and defects in the crystal. Only a slight decrease in lifetime was observed in our crystals, same as for bulk grown crystals. This attests to the crystal quality and demonstrates the viability of this growth technique for material optimization and comprehensive study of energy pathways in laser crystals.

The lasing transition between the 4I11/2 and 4I13/2 of Er3+ in YAG is self-terminating due to the significantly longer lifetime of 4I13/2. This paper describes the codoping of Er:YAG with Eu and Tb as deactivator ions to reduce this undesirable effect by energy transfer between the 4I13/2 of Er3+ and the codopant ions. Unique grouping of levels in Eu3+ and Tb3+ provide numerous levels between 4I13/2 and the ground state for fast multiphonon relaxation but none near 4I11/2. Crystals of 16% Er:YAG codoped with different Eu and Tb concentrations were grown by the laser-heated pedestal growth technique for measuring lifetimes of excited Er3+ ions. We found that with both Eu and Tb, doping at ~1% increased the ratio of upper to lower state lifetimes from 0.02 to better than 0.3. Higher doping did not increase this ratio as quenching of 4I11/2 became significant. This is likely due to cross relaxation involving ground state ions of the codopant. Although unable to achieve a ratio of unity and above, codoping Er:YAG should still lead to improvement in pulsed laser performance.

Previous studies have shown the N2O/CO/Mg reaction to be capable of efficiently producing Mg(3P) in large concentrations.1,2 On the basis of the favorable energy level positions of Sm, we have embarked on a study of the feasibility of a visible chemical laser through transfer of energy from Mg(3P) to Sm. Fluorescence measurements from flowing mixtures of Mg and Sm vapors under both pulsed and cw laser excitations on the Mg(1S—3P) transition have been made. Intense emissions from a number of Sm transitions in the green region were observed. Preliminary time-resolved fluorescence decay data taken over a range of Sm densities yielded a quenching rate for Mg(3P) approximately ten times the gas kinetic rate. Relative steady-state fluorescence intensity measurements showed that nearly all the collisions result in the excitation of Sm. These findings indicate that an efficient visible chemical laser based on the Mg(3P)/Sm system may be possible if a suitable gas for deactivating the chosen lower laser level can be identified.

Amplification of a diffraction-limited Stokes beam in a hydrogen Raman amplifier pumped by a severely aberrated XeC1 laser has been studied experimentally. Spatial quality of the amplified Stokes beam and conversion efficiency from the pump laser were measured. Numerical study of this process using a two-dimensional propagation code that includes pump depletion was performed. The simulation shows that the quality of the amplified Stokes beam depends critically on the absence of any near-axial components in the pump laser. These components of the pump can cause phase matched four-wave mixing interactions with the Stokes, leading to increased angular divergence of the amplified Stokes beam and the development of secondary sidebands in the far field. An optical integrator was used to focus the poor quality pump beam into the amplifier and to remove all near-axial components in the pump field. The diffraction-limited nature of the input Stokes beam was then preserved in the amplified Stokes beam. A power conversion from the aberrated pump to the Stokes beam of the order of 30% was observed. The far field intensity of the Stokes beam increased by a factor of 5000 over that of the original pump.

Single crystal materials in fiber form can potentially lead to highly efficient nonlinear optical devices at low power levels. The possibility of producing high quality crystal fibers by the laser heated miniature pedestal growth technique has previously been demonstrated.1 The full exploitation of such fibers would require the development of suitable procedures for their poling and cladding, which are essential for phase matching and core reduction purposes. We have used the same miniature pedestal growth technique to grow a-axis LiNbO3 fibers with cross-sectional dimensions of a few tens of microns. These fibers were subsequently poled by a simple procedure which preserved their smooth surface morphology. The single domain fibers prepared this way were then clad through multiple energy implantation with He ions starting at 5 MeV in decreasing steps.

SUMMARYWe have demonstrated that the laser heated pedestal growth technique can be a fast andcost effective way to grow rare earth doped garnets for laser material evaluation. Crystalcharacterization and laser induced fluorescence study show that they are reliable substi-tutes for bulk grown crystals in spectroscopic and energy kinetics studies. This growthtechnique should be used more extensively in future to survey laser materials and identifyoptimum dopant concentration for bulk crystal growth. As illustrated by our measurement ofthe interaction microparameter, the LHPG method is an invaluable research tool to supplycrystals of different dopant concentrations for study of ion -ion interactions that are re-sponsible for various energy transfer and relaxation phenomena in single crystals. 5. ACKNOWLEDGMENTSThe authors gratefully acknowledge helpful discussions with R. L. Byer, M. M. Fejer andG. A. Magel of Stanford University during the design stage of our growth facility. The authors also wish to thank G. Pidick, E. Roubal, S. Valenti and M. Williams for their tech-nical support. This work was supported by the Florida High Technology and Industry CouncilApplied Research Grants Program.

Using a propagation cell that discriminated against the buildup of stimulated Raman emission, we succeeded in observing self-focusing in pressurized air without interference from any competing nonlinear process. Measurements were made for air pressures between 20 and 40 atm. The data yielded a nonlinear refractive index n2. = (2.9 ± 0.3) × 10−16 esu per atmosphere of air at 300 K for a 308-nm laser beam.

We describe experimental and theoretical investigations of beam cleanup with highly aberrated pump beams in the intensity-averaging regime. Distortion-free amplification of a diffraction-limited Stokes beam is demonstrated in a crossed-beam geometry with a pump beam aberrated to 120 times its diffraction limit, resulting in a brightness increase of 5000 times. Moderately aberrated pump beams produce off-axis Stokes components, while collinear interactions introduce distortion on the Stokes beam. Phase conjugation is combined with stimulated Raman scattering to remove both the aberrations of the pump beam and the aberrations on the Stokes beam itself.