Absorption in the near-ultraviolet wing of the Kr2F*(410 nm) band

An intracavity laser technique has been used to study the absorption of electron-beam pumped Ne/Kr/F2gas mixtures (196 and 300 K) in the "blue wing" of the Kr2F emission continuum. The experiments were conducted at 358 nm using theupsilon' = 0 rightarrow upsilon" = 1transition of the N2(C rightarrow B) laser. Comparing the results with the predictions of a computer model, the species primarily responsible for absorption have been identified as Ne+2, Kr+2, and Kr2F*. The photoabsorption cross sections for Ne+2and Kr2F (Kr+2F-) at 358 nm have been estimated to be8.1 cdot 10^{-19}and5.4 cdot 10^{-18}cm², respectively. The Kr2F* absorption cross section is roughly 20 percent of that reported for Kr+2at the same wavelength. The fluorescence efficiency of Kr2F* ine-beam excited 94.93 percent Ne/5 percent Kr/0.07 percent F2(P_{total} = 4000torr) gas mixtures has been found to be a factor of 2.8 higher than that of the N2(C rightarrow B) band in Ar/5 percent N2mixtures. Also, the rate constant for quenching of Kr2F* by F2was measured to be(4.1 pm 0.5) cdot 10^{-10}cm³. s^-1at 300 K and(3.0 pm 0.5) cdot 10^{-10}cm². s^-1at 196 K.     

High-pressure xenon laser at 1730 Å

Experimental measurements are reported of optical gain due to stimulated transitions between the lowest-bound diatomic states of xenon (Xe) and the repulsive ground state. The optical gain was greatest at a wavelength of (1730 ± 10) Å, where the effective gain cross section is estimated to be7 times 10^{19}cm².     

CW laser operation of Nd:YLF

CW laser operation of Nd:YLF is reported for the first time and, in a comparison to Nd:YAG, exhibits a lower threshold and higher single-mode average power. The TEM00mode volume of Nd: YLF was observed to be a factor of four larger than Nd:YAG, resulting in twice the TEM00mode average power. This result is attributed to the substantially lower thermal lensing of YLF with respect to YAG. In comparative measurements the stimulated emission cross section of Nd:YLF was found to be1.8 times 10^{-19}cm²for the π oscillation and1.2 times 10^{-19}cm²for the σ oscillation, as compared to2.4 times 10^{-19}cm²for Nd:YAG. The spectroscopic and lasing parameters of Nd:YLF indicate a potential for this material in high peak and average powerQ-switched applications.     

Amplification cross section of the 1.052-µ transition of Nd3+in POCl3- SnCl4-(H2O) system by three different methods

We report the measurement of the amplification cross section σ21of the Nd³⁺ion in the POCl3-SnCl4-(H2O) system by three different methods. The first is based on the simultaneous measurement of the variation of fluorescence andQ-spoiled laser emission. The second is purely spectroscopic. The third is based on the measurement of k12at several temperatures. The two last methods give similar results. The most probable value issigma_{21} = 8.5 times 10^{-20}cm². An explanation for the lowest valuesim 6 times 10^{-20}cm²found with the first method is given.     

The influence of the optical stark shift on the two-photon excitation of the molecular hydrogen E, F1Σ+gstate

The first demonstration of the use of the optical Stark effect to secure resonance for a two-quantum process in the ultraviolet is reported. Following excitation of molecular hydrogen by 193 nm radiation, intense stimulated emission on both the Lyman and Werner bands is observed. The Werner (2-5)Q(1)transition at 117.5 nm exhibits a conversion efficiency of ∼0.2 percent. It is found that electron collisions with excited molecules provide the most probable mechanism for excitation of theC^{1}Pi_{u}levels with a rate constant estimated to bek_{e} sim 7 times 10^{-6}cm³/s.     

Ground state ESR measurements of ruby during laser action

The use of electron spin resonance for measurement of the ground state population (GSP) of Cr³⁺in a ruby rod during optical pumping is described. For a 7.7 cm long rod at 90°K and a mirror reflectance productR_{1}R_{2} > 0.08, the GSP at laser threshold was found to be 55 ± 5 percent in good agreement with theory and previous optical measurements. At room temperature, a limiting value of approximately 30 percent for the GSP was approached at high pump energies. Observations of the relativeR_{1}(3/2), R_{1}(1/2)thresholds at 90°K as a function of mirror reflectivity indicated that the²E excited state absorption cross section at the laser wavelength is less than5 times 10^{-21}cm². Detection of total internal reflection oscillations in cooled ruby lasers from ESR observations is also described.     

Tunable alexandrite lasers

Wavelength tunable laser operation has been obtained from the solid-state crystal alexandrite (BeAl2O4:Cr³⁺) over the continuous range from 701 to 818 nm. The tunable emission was observed at room temperature and above in a homogeneously broadened, vibronic, four-level mode of laser action. In this mode the laser gain cross section increases from7 times 10^{-21}cm²at 300K to2 times 10^{-20}cm²at 475K, which results in improved laser performance at elevated temperatures. Efficient 2.5 percent, low-threshold (10 J) operation has been obtained with xenon-flashlamp excitation of the 6 mm diameter × 76 mm length laser rods. Output pulses of greater than 5 J and average power outputs of 35 W have been demonstrated, limited by the available power supply. The emission is strongly polarizedEparallelb, with a gain that is 10 times that in the alternate polarization. The 262 μs, room-temperature fluorescence lifetime permits effective energy storage andQ-switched operation. TunableQ-switched pulses as large as 500 mJ have been obtained with pulsewidths ranging between 33 and 200 ns depending on the laser gain. Laser action has also been demonstrated on the high-gain (3 times 10^{-19}cm²emission cross section)Rline at 680.4 nm and is also polarizedEparallelb. This three-level mode is analogous to the lasing in ruby except that the stimulated emission cross section in alexandrite is ten times larger than for ruby.     

Stimulated-emission cross section and inversion lifetime in a three-atmosphere iodine photodissociation laser

An iodine photodissociation laser has been operated at three atmospheres by adding an inert gas to the laser medium. With three atmospheres of helium added a stimulated-emission cross section of2 times 10^{-19}cm²and an inversion half-life of 110 μs was observed.     

Spontaneous emission lifetime of the C → A band of the XeF molecule

The radiative lifetime of the blueC rightarrow Atransition of XeF has been measured to be 93 ± 5 ns by monitoring the exponentially decaying 460 nm emission following rapid electron impact dissociation of XeF2. By varying the XeF2partial pressure, the rate constant for quenching of XeF (C) by XeF2was determined to be(1.8 pm 0.5) cdot 10^{-10}cm³. s^-1. Finally, knowledge of the XeF B and C state lifetimes yields a revised value of 610 ± 60 cm^-1for theBtoCstate energy defect.     

Study of the XeCl laser pumped by a high-intensity electron beam

We present the results of a detailed experimental study of the XeCl laser pumped by a high-intensity electron beam. The laser system was optimized as an oscillator for mixtures of Xe and HCl with Ne, Ar, and Kr diluents. The peak intrinsic efficiency (laser energy out/electron-beam energy deposited) was near 4.5 percent for each of these diluents. Small-signal gain and background absorption were measured as a function of electron-beam deposition rate from 0.4 to 6 MW/ cm³. The ratio of small-signal gain to absorption was found to be constant over this range with a value of ∼5. Measurements of absorption in the presence of a large photon flux indicated that there was no appreciable saturable contribution to the absorption. Measurements of fluorescence from theBandCstates indicate that collisional mixing between these states is very rapid. The formation efficiencies of theBandCstates are estimated to be 0.15 and 0.05, respectively. A vibrational relaxation rate of between 1 and1.5 times 10^{-10}cm³. s^-1was determined. The effect of this finite relaxation rate is to reduce the energy available to the stimulated process by a factor of 0.67-0.75. Estimates of the XeCl* deactivation rates by HCl and electrons were also obtained. A value of1.7 times 10^{-9}cm³. s^-1was obtained for quenching by HCl, and a value ofsim 1 times 10^{-7}cm³. s^-1was estimated for electron deactivation.     

A flashlamp-pumped, Q-switched Cr:Nd:GSGG laser

A long-pulse Cr:Nd:GSGG laser was operated at almost 2 J output energy and almost 5 percent efficiency, using an uncooled pump cavity. An Nd:YAG rod in the same pump cavity produced 3.75 percent efficiency. Using a water-cooled pump cavity of standard design, the thermal focusing of Cr:Nd:GSGG was found to be almost six times that of Nd:YAG for the same flashlamp input energy. The thermal birefringence of the GSGG was also observed to be significantly higher than that of YAG. The performance of aQ-switched Cr:Nd:GSGG laser was characterized and compared to the predictions of a mathematical model for the laser. This yielded an estimate of4.2 times 10^{-19}cm²for the peak stimulated emission cross section of Nd³⁺in GSGG. Using the same technique for Nd:YAG yielded a value of9 times 10^{-19}cm².     

Nonlinear refractive index and "DC" kerr constant of liquid CS2at 10.6 µm

The "dc" Kerr constant of CS2has been measured at 10.6 μm and found to be(2.9 pm 0.8) times 10^{-8}statvolt^-2cm. This yields a value of(2.1 pm 0.7) times 10^{-11}statvolt^-2cm²for the nonlinear refractive index.     

Deep red laser emission in Ho:YLF

Laser operation of the⁵S2→⁵I7transition in 2 percent Ho:YLF at room temperature is reported. Oscillations atlambda = 750nm were obtained in flashlamp and dye laser pumped experiments. Thresholds of 4 J/cm and3 times 10^{-4}J/cm were observed in flashlamp and laser pumped operation, respectively. The 750-nm transition in the Ho:YLF is a four-level laser with a stimulated emission cross section ofsigma = 9.7 times 10^{-19}cm².     

Growth, optical properties, and CW laser action of neodymium-doped gadolinium scandium aluminum garnet

Investigation of the congruent melting rare-earth aluminum garnet Gd3Sc2Al3O12(GADSCAG) has been made. The optimum crystal growth parameters for the undoped material are a rotation rate of 20 r/min and a growth rate of 4.6 mm/hr along thelangle111rangledirection. For Nd³⁺-doped crystals the linear growth rate is 2 mm/h. The optical properties of Nd:GADSCAG which are of interest for laser operation were also determined. The stimulated emission cross section of the 1.06-μ transition in Nd³⁺at room temperature is(3.2 pm 0.3) times 10^{-19}cm², the fluorescence lifetime is256 pm 8 mus at an Nd³⁺ion density of 1 atomic percent in the crystal and the integrated peak absorption cross section in the strongest pump band (0.81 μ) is3.8 times 10^{-19}cm², A comparison of the CW laser performance of identical ND:YAG and Nd:GADSCAG rods is presented.     

Formation kinetics of the triatomic excimer Ar2F*

Detailed fluorescence measurements of electron beam-excited high pressure mixtures of Ar/F2and Ar/NF3have been made in order to investigate the processes leading to the formation of Ar2F*. Three-body collisional quenching of ArF* has been identified as a major formation mechanism. The third-order rate constant for this reaction has been measured to bek_{1} = (1.2 pm 0.2) times 10^{-30}cm⁶. s^-1. In addition quenching rates for collisional de-excitation of Ar2F* by argon and the fluoride donors NF3and F2have been determined. The radiative lifetime has been measured as 219 ± 15 ns. The possible formation of Ar2F* from long-lived excited argon neutrals when using intense excitation densities and low-donor pressures is also briefly discussed.     

Vibration-vibration energy transfer in the v3mode of CO2

The vibration-vibration energy transfer of CO2gas initially excited to the first asymmetric stretch level (00⁰1) has been observed. Collisional pumping to the (01¹1) combination level is measured by monitoring the fluorescence due to the (01¹1) → (01¹0) band. The rate constant for the process: CO2(01¹1) + CO2(00⁰0) → CO2(00⁰1) + CO2(01¹0) is found to be(5.3 pm 1) times 10^{6}s^-1torr^-1.     

Birefringence in single-mode optical fiber due to elliptical core deformation and stress anisotropy

A formula for the difference between propagation constants of two polarization modes caused by elliptical core deformation and stress anisotropy is given for single-mode optical fibers. Birefringence in circular and elliptical core fibers subject to an externally applied uniaxial pressure are measured. Birefringence caused by elliptical core deformation and stress anisotropy are experimentally separated by measuring their wavelength dependences. A value of3.36 times 10^{-10}cm²/gram weight (gw) (=3.43 times 10^{-12}m²/N) is obtained for the stress-optical constant of silica fibers. Residual stress corresponding to external pressure of 240 gw/cm is observed for a fiber with 0.35 core ellipticity.     

Spectroscopy and lasing of a high Nd concentration Al-phosphate glass

An Al-phosphate glass containing Nd³⁺in concentrations ranging from3 times 10^{20}to2.7 times 10^{21}ions/cm³has been prepared and investigated spectroscopically. Different ways of measuring the⁴F3/2→⁴I9/2emission cross sections yield values between1.96 times 10^{-20}and2.7 times 10^{-20}cm². At the highest concentration the decay time is 50 μs, while the radiative lifetime is estimated to begeq446 mus. Lasing experiments were performed by pumping thin platelets of glass coaxially with a dye laser. Cross sections, losses, and differential efficiencies are derived from these experiments. The status of high concentration glasses versus stoichiometric Nd compounds is reviewed.     

Optical absorption and fluorescence studies in high pressure cesium-xenon mixtures

The pressure and temperature dependent absorption and fluorescence spectra of the cesium-xenon (CsXe) molecule have been examined. In contrast to previous investigations of the alkali-rare gas molecules, cesium atomic states that have weakly allowed optical transitions have been studied and have been shown to form excimer levels that are attractive for application as potential dissociation lasers. In particular, the (Cs[7^{2}S]Xe)* excimer appears promising as a source of high-energy laser radiation due to 1) its large dissociation energy (0.132 eV), 2) its stimulated emission cross section ofsimeq10^{-17}cm², and 3) its small population threshold inversion densities (simeq10^{13}cm^-3).     

Fluorescence and oscillation characteristics of LiNdP4O12lasers at 1.317 µm

Spectroscopic data and laser oscillation characteristics of the 1.317 μ line in lithium neodymium tetraphosphate (LNP) are reported. A stimulated emission cross section of this transition was spectroscopically determined as7.1 times 10^{-20}cm², which corresponds to 1/4.5 of that at the 1.047-μm transition. Cross-section temperature dependence, laser cavity loss, threshold versus crystal length, and threshold temperature dependence were measured experimentally. Since resonant loss was negligible at the 1.317 μm line, room temperature threshold is lower than that at 1.047-μm in the case of long crystal, and threshold temperature dependence is weaker than that at 1.047 μm. A miniaturized LNP laser, using a graded index fiber as a focusing medium, is also shown. LED pump intensity required to obtain a constant output is compared for 1.047- and 1.317-μm wavelengths. The 1.317-μm line seems to be useful as miniaturized optical sources in optical communication systems, since required intensity is around several W/cm²for the side pump, and the wavelength corresponds to the most transparent band of ultra low-loss optical fibers.