Induced-emission cross sections for the4F3/2→4I13/2transition in neodymium laser glasses

Induced-emission cross sections for the⁴F_{3/2} rightarrow⁴I_{13/2}transition of Nd³⁺in several commercial and experimental laser glasses have been determined using spectroscopic data and the Judd-Ofelt treatment of electric-dipole transition probabilities.     

A laser augmented reaction: SF6+ SiH4→S*2+ SiF4+ HF + H2· retention of isotopic selectivity during detonation

A single unfocused pulse of a free running CO2laser, area ∼ 8 cm², initiates an explosive reaction between SF6and SiH4. This occurs at a minimum energy of 4 J [full width at half maximum (FWHM)sim 1.5 /mus] of which about one half is absorbed in an 8 cm long cell; total pressure 12 torr; 0.65 <p(SiH4)/p(SF6) < 1.8. The spectral and temporal distributions of the emitted chemiluminescence depend sensitively on the fuel to oxidizer ratio, and on the pulse energy; we investigated the range 4 → 20 J. The principal emission is due to S2(B^{3}Sigma-_{u} rightarrow X^{3}Sigma-_{g}). Transitionsupsilon' (0-4) rightarrow upsilon" (2-15)were recorded. In the³Sigma-_{u}state, vibrational temperatures range from 3000-13000 K. The luminosity peaks sharply at (SiH4)/(SF6) = 1.0 ± 0.05. On each side of the maximum of the emission versus composition curve [at (SiH4)/(SF6) ≈ 0.95 and 1.22, for a 12 J pulse] the residual SF6(0.2-0.5 percent of initial amount) is enriched in³⁴SF6; the observed fractionation factors at these two compositions are 8 ± 2. The separation between the two sharply peaked optimum compositions appears to increase with increasing pulse energy. Preliminary results with other fuels suggest that the concurrent absorption of CO2laser radiation by the fuel, as well as a highly exothermic reaction, are pre-requisite for fine tuning of composition, injected power, and total pressure for optimum isotope fractionation.     

Stimulated emission at 2.04 µm in Ho3+-doped ErVO4and YVO4

We have observed both CW and pulsed laser operation in Ho³⁺-doped ErVO4and YVO4at 2.0416 μm and 2.0412 μm, respectively. Both laser emissions are linearly polarized. For this preliminary experiment the crystals were cooled to liquid nitrogen temperature and pumped in two configurations using an argon-ion laser and a xenon flashlamp.     

Photoexcitation and photodissociation lasers--Part I: Nitric oxide laser emissions resulting from C(2π) → A(2Σ+) and D(2Σ+) → A(2Σ+) transitions

-1-μm laser emission was detected when NO or NO2was flash-photolyzed, with or without dilution, in the vacuum UV above 165 nm. The emission was identified as theC(²π)rightarrow A(²Sigma+)     

High-efficiency, high-power difference-frequency generation at 2-4 µm in LiNbO3

High-efficiency generation of high-peak power and high-average power difference-frequency radiation, continuously tunable over the range of 2 to 4 μm, has been achieved by mixing the Nd:YAG laser radiation with the output of a near-infrared dye laser pumped by the second harmonic of the same Nd:YAG laser in LiNbO3. A peak power as high as 1.6 MW with an average power of 130 mW was obtained near 2.3 μm.     

Resonantly enhanced 26 GHz parametric upconversion of CO2laser in NH3

Resonantly enhanced three-wave mixing of the 10.784 μmR(18) line of the C¹³O2¹⁶laser and microwave radiation at 26.378 GHz in Stark tunable N¹⁴H3has resulted in upconverted parametric output at 10.774 μm. The energy levels of N¹⁴H3involved in the interaction and the apparatus used in the experiment are described. Experimental results showing saturation of the parametric signal with increasing N¹⁴H3pressure, input microwave power, and input laser power are described.     

Near single-line operation of a free-burning CS2/O2/N2O flame laser with a nondispersive optical cavity

The CS2/O2/N2O flame laser has been operated for the first time under conditions in which the spectral output is nearly single line. This transition is theP_{10-9}(17) of CO at 5.4265 μm, the same transition which was observed to oscillate in single-line fashion by Hirose et al. in an electrically initiated CO chemical laser. It is suggested that the unique behavior of this line may be due to its close proximity to aPbranch transition in an adjacent band, namely theP_{9-8}(23) line, such that the gain profiles of the two lines overlap. Calculations suggest that at the conditions of these experiments, the separation of the line centers for this pair is about 0.3 Å or less. TheP_{10-9}(17) transition was also found to be totally absent under certain conditions of high multiline power, particulary at low O2and N2O flows. This may be due to absorption by a high-bandRbranch transition at 5.4266 μm, namely theR_{15-16}(32) line.     

Efficient multikilowatt mid infrared difference frequency generation in CdGeAs2

Multikilowatt mid infrared emission with high pump photon conversion efficiency (∼ 15 percent) has been obtained by difference frequency generation in CdGeAs2utilizing the double wavelength output from a grating tuned twin-cavity TEA CO2system, one signal of which is frequency doubled to provide efficient synchronized sources for both pump and idler. Tuning over a spectral range8-14 mum can be achieved and further extended to 17 μm using 12.8 μm emission from an efficient TEA CO2pumped NH3laser.     

New wavelengths of the YAlO3: Er laser

In addition to the 1.662 μm laser transition, stimulated emission at three new wavelengths at 1.677, 1.706, and 1.729μm have been observed at 300 K in the YAlO3:Er crystal with an activator concentration of 1.25 weight percent.     

Characteristics of room-temperature 2.3-µm laser emission from tm3+in YAG and YAlO3

The relaxation of low-lying excited states of Tm³⁺ions doped in YAG, YAlO3, and Y2O3due to photon and phonon emission is studied theoretically. Stimulated emission cross sections (integrated over frequency), fluorescence lifetimes, and radiative quantum efficiencies are calculated and their implications for laser operation on the 2.3-μm³F4→³H5line of Tm³⁺are discussed. The calculations, based on a few phenomenological parameters which have been determined by others, are easily generalizable to other host materials and other rare-earth (RE) ions. Room-temperature pulsed laser emission from Tm³⁺ions near 2.3 μm was observed on one line in Tm:Cr:YAG, and on four lines in Tm:Cr:YAlO3. Lower oscillation thresholds were generally obtained in the YAlO3 rods, consistent with the theory presented. A threshold of 31 J was obtained with a Tm:Cr:YAlO3rod at 2.274 μm. In the free-running pulsed mode, peak power levels up to several hundred watts and total output energies up to 12 mJ/pulse were observed. Other general, observed operating characteristics are discussed.     

Characteristics of MOSFET prepared on Si/MgO.Al2O3/SiO2/Si structure

A new silicon on insulator (SOI) wafer with epitaxial-Si/ epitaxial-MgO.Al2O3(0.1 µm)/SiO2(0.5 µm)/     

Electronic- and phonon-terminated laser emission from Ho3+in BaY2F8

Infrared spontaneous and stimulated emission from Ho³⁺in BaY2F8is reported. In addition to the familiar⁵I_{7} rightarrow⁵I8transition at 2 μ,⁵F_{5} rightarrow⁵I5emission at 2.4μ and⁵I_{6} rightarrow⁵I7emission at 2.9μ are discussed. There are several unusual features of the 2-μ laser emission. At room temperature, phonon-terminated laser emission is observed at 2.171 μ. At 77 K a complex CW laser output is observed in a wavelength interval lying on the shoulder of a fluorescence line. The complex output is attributed to oscillation in transverse modes of the resonator. Oscillation is not observed in the strongest emission line, despite a large terminal state splitting of 310 cm^-1. These results are explained on the basis of a theory developed earlier for transition metal ion lasers. The validity of the model is supported by demonstrating the tunability through loss modulation predicted by theory. The observation of these effects is made possible by the very low internal scattering loss in the crystals. The⁵F_{5} rightarrow⁵I5laser lines near 2.4 μ represent relatively low gain transitions with pulse durations limited by accumulation in a longer lived terminal state. The dynamics of laser emission indicate the possible absence of thermal equilibrium in the excited state. For the 2.9-μ transition the bottleneck posed by a longer lived terminal state may be eliminated by the addition of Eu³⁺or Pr³⁺, but laser emission could not be obtained.     

Laser oscillation at 3-4 µm optically pumped InAs1-x-ySbxPy

Quaternary InAs1-x-ySbxPy) and ternary InAs1-xSbxhave been grown on InAs substrates using liquid phase epitaxy. The quaternary layers are lattice matched to InAs fory = 2.2x, and have bandgaps greater than InAs. The ternary layers have lower bandgaps than InAs, but have larger lattice constants. Reasonable quality growth has been obtained up tox = 0.15where the luminescence peak is shifted to ∼4 from 3.1 μm and the lattice mismatch is ∼0.01. Optically pumped laser emission at 3.1 μm has been observed from 77 to 100 °K using an InAs active layer with InAs1-x-ySbxPyclading layers. Laser emission at 3.9 μm has been observed from 77 to 125 °K using a InAs1-xSbxactive layer, withxsim 0.13, and InAs cladding layers. Laser emission from intermediate ternary compositions has also been observed.     

Laser action from Ho3+, Er3+, and Tm3+in YAlO3

Laser action has been observed for the following rare-earth ions in YAlO3:Ho³⁺(sensitized with Er³⁺and Tm³⁺), Er³⁺, and Tm³⁺(sensitized with Er³⁺) at wavelengths of 2.123, 0.851, and 1.861 μm, respectively. Measurements of spectroscopic properties, fluorescence kinetics, and laser performance of these ions in YAlO3are reported.     

Submillimeter laser action of CW optically pumped CD2Cl2, CH2DOH, and CHD2OH

More than 30 laser lines, several of them with an intensity in the order of mW have been obtained in the submillimeter wavelength range from 100 to 900 μm by optically pumping the deuterated molecules of dichloromethane (CD2Cl2) and methanol (CD2HOH, CH2DOH) with a step tunable CO2laser.     

Laser-induced breakdown in crystalline and amorphous SiO2

The 1.06 μm breakdown thresholds of crystalline and amorphous SiO2were compared. These materials showed dependences of the breakdown threshold on the focal volume which are consistent with a multiphoton-assisted electron avalanche damage mechanism.     

Pulsed laser action in LiYF4:Er3+, Ho3+at 77°K

Pulsed laser action at 77°K has been demonstrated in LiYF4:Er³⁺, Ho³⁺with an emission wavelength of 2.066 μ. The laser transition is the⁵I_{7} rightarrow⁵I8in trivalent holmium, and there is evidence of energy transfer from erbium to holmium. The fluorescent lifetime is approximately 20 ms, and the pulsed threshold is 40 joules.     

Laser induced damage, nonlinear absorption, and doubling efficiency of LiO3

Laser-induced damage thresholds of single crystal LilO3have been studied using picosecond pulses at 1.06 μm and 0.53 μm. These thresholds depend on wavelength, on crystal orientation, and on the number of times the sample has been irradiated. In addition, the doubling efficiency at high irradiance levels was observed to be a decreasing function of irradiance beyond a critical value. We present evidence to show that this results from the onset of optical parametric down conversion. In separate nonlinear transmission studies, reversible nonlinear transmission of 1.06 μm light was measured, and in self-diffraction experiments, both reversible and irreversible optically-induced complex index of refraction changes at 0.53 μm were observed.     

CO(v = 2:1) laser transitions from He-air-CH4

A flowing electrochemically excited liquid-nitrogen-cooled He-air-CH4-(CO) laser was operated inQ-switched fashion yielding 20 CO laser lines below 5.0 μ. These laser lines were measured to occur from 4.7848 to 4.9880 μ. The lines were all identified to result fromP(J)_{upsilon,upsilon'}CO vibrational-rotational transitions as low asupsilon = 2:1. Nine suchupsilon = 2:1transitions were measured.     

Far infrared laser emission from15NH3optically pumped by a CW sequence band CO2laser

Two new coincidences between theP(31) andP(35) CO210.6 μm sequence band emission lines and the¹⁵NH3absorption lines have been found to produce far infrared (FIR) emission lines atlambda = 111.9and 218 μm. In addition, the known coincidence between the regularR(42) 10.6 μm band CO2emission line and theasR