CW 10.6-µ CO2laser pumped by the chemical reaction of nitric oxide with nitrogen atoms

The operation of a CW CO2laser pumped by vibrationally excited nitrogen generated by the reaction of nitric oxide with atomic nitrogen is reported. 15-mW output power at an overall chemical efficiency of 1 percent has been obtained. The population inversion density of the system has been determined from gain measurements.     

Self-focusing of 10.6-µm radiation in liquid CS2

Self-focusing of 9-kW CO2laser pulses was observed in liquid CS2. The calculated coefficient of nonlinear index of refraction (n2) from experimental data is approximately 10^-17MKS, which is nearly three orders of magnitude larger than the nonlinear index coefficient observed for visible radiation.     

Saturation of hot CO2by short 10.6 µm laser pulses

Saturation of the absorption of hot CO2by 1.6 nsP(18)andP(20)laser pulses at 10.6 μm has been measured. Coherent propagation calculations with no fitting parameters are in good agreement with the data and are consistent with a substantial hot-band contribution to theP(20)saturation.     

Gain characteristics of CO2laser amplifiers at 10.6 microns

Single-pass gain at 10.6 microns has been studied parametrically in nonflowing CO2or buffered CO2amplifying media. The gain profile across the amplifier diameter and integrated gain both were determined. Parameters varied included buffer gas type, mixture ratio, gas pressure, amplifier bore, discharge current, and wall temperature. Tube bores of 12, 22, and 34 mm and buffer gases of H2, He, Ne, A, and N2were studied. Optimum gain is relatively independent of current density, but decreases with increasing wall temperature. The pressure-diameter relationshipP_{CO_{2}} cdot D sim 4torr-cm was found to hold for CO2, CO2:He, and CO2:N2amplifying media at optimum gain. The gain depends strongly on the CO2partial pressure and is relatively insensitive to the buffer gas pressure except for the case of H2. The maximum gain decreased slowly with increasing amplifier diameter. The highest gain, 1.7 dB/meter, was achieved with a helium buffer gas in amplifiers with a diameter of 22 mm or less. No gain saturation was detected for a 30-dB range of input signal power, from a milliwatt to a few watts. Spectrograms showed that the principal spontaneous emission from CO2:He amplifiers in the 2000-7000-Å range consisted of CO bands; no CO2bands or He line spectra were observed.     

Observation of power-dependent distortion of an infrared beam at 10.6 µm from a CO2laser during propagation in liquids

This paper reports the first experimental verification of the existence of the self-induced effect of spread and serious distortion of the infrared beam from the CO2laser system at 10.6 μm when propagating in various liquids. The power-dependent shape of the laser beam after passage through the liquid cell was visibly displayed on the Kalvar film by virtue of the thermal development method originally invented by our laboratory. The phenomenon observed is considered as having a thermal origin due to the partial absorption of the infrared beam; yielding localized heating, and thereby thermal convection which causes a complex change of the refractive index around the beam passing through the medium. The interference fringes found in the distorted beam pattern are likely attributed to the spherical aberration in the thermal defocusing lens induced in the material by the laser beam itself.     

12 µm Raman lasers in NH3pumped by low-power CO2laser pulses

We report the operation of optically pumped 12 μm lasers in NH3using peak pumping powers as low as 2 W. These low pumping powers represent a 1-2 order-of-magnitude improvement over previously published threshold values. Measurements of the lasing offset frequency clearly demonstrate that a two-photon Raman process is responsible for optical gain at 12 μm. In light of our results, we discuss the feasibility of an optically pumped CW 12 μm laser.     

Comparison of computer simulation and experimental results for a 16 µm HBr/CO2laser

An improved version of a computer model simulates 16μm laser output from an optically pumped HBr/CO2/Ar laser cavity. A rate equation approach is used to examine the time history of vibrational and rotational excitation and subsequent lasing from the HBr/ CO2gas mixture. Rotational nonequilibdum phenomena in HBr and CO2are included. The effect of bleaching a particular vibrational-rotational transition with optical saturation is modeled in detail. The results of the computer simulation are compared to the laboratory observations from two separate experiments. The model predicts accurately the effect of changing partial pressures of the constituent gases on 16μm power and energy. The model reveals the important kinetic mechanisms yielding these trends. Finally, the model is modified to simulate optical pumping by an HF laser of an HF/CO2/Ar gas mixture. A case by case comparison with the results of the HBr model prediction show significantly lower 9.4 μm powers and energies for any given HF pressure and no evidence of 16μm laser output from the HF/CO2gas mixture.     

Whispering-gallery CO2laser

The design and operation of a CW CO2laser based on the whispering-gallery principle is reported. The optical cavity consists of a portion of the equatorial region of a torus terminated by two flat mirrors. In agreement with theoretical expectations, the output beam is found to be TE polarized, and to consist of low-order Airy-Hermite-Gaussian modes.     

Q-switched CO2laser

Experimental studies of a rotating-mirrorQ-switched CO2laser have been undertaken to obtain high peak powers at 10.6-μ wavelength. TheQ-switched pulse has a temporal structure consisting of two intensity peaks and is similar to the temporal behavior of a slowQ-switched CO2laser. Based on the gas pressure dependence it appears that the pulse structure and duration are influenced by collision-induced relaxations of the laser medium. Using an oscillator-amplifier system peak powers of 120 kW with pulsewidths of 200 ns have been obtained.     

Sensitivity measurement of a 10.6-µm parametric upconverter

The sensitivity of a parametric upconverter for the detection of 10.6-µm radiation was measured. 10.6-µm radiation was mixed with the 1.06 µm beam of an Nd :YAG laser in properly oriented single-crystal proustite. The upconverted output at 0.967 µm was then detected by an S-1 photomultiplier tube. NEP of 1.1×10^-9W . s^½was measured.     

Three-frequency heterodyne detection of 10.6-µm laser signals

A three-frequency 10.6-μm heterodyne receiver was demonstrated experimentally. Narrow-band reception of a 40-MHz IF was realized without tracking of the carrier frequency by the local oscillator laser. A signal-to-noise ratio within 1 dB of the theoretical value was measured for large SNR.     

10.6-µm FM-chirp radar using narrow-band correlation detection

We report the demonstration of high-resolution 10.6-μm radar-range resolution using a broad-band FM-chirp signal, but requiring only narrow-band performance in a heterodyne detector.     

A variable 10.6-µ attenuator

A variable CO2laser attenuator with a dynamic range of 33 dB, large power handling capability, and reproducible attenuation has been constructed.     

Effects of gas flow on gain of 10.6 micron CO2laser amplifiers

Small-signal gain of flowing gas CO2laser amplifiers at 10.6 microns has been optimized for media including pure CO2CO2: N2, CO2: He, CO2: CO, CO2: O2, CO2: N2: He, CO2: CO : He, and CO2: CO : N2. Optimum gain of all flowing gas systems studied increases monotonically with increasing gas flow rate. In the low CO2flow rate region, 10 < RCO2: < 50 cm³/min, gas flow enhances the gain most for systems containing N2. Results provide strong evidence that the rapid increase in gain with flow rate in CO2: N2mixtures is due to removal by convection of the dissociated product CO. For 50 < RCO2< 200 cm³/min, a slow linear increase in gain of all gas mixtures with increasing flow rate occurs and is attributed to the cooling of gas temprature by convection. A stronger dependence of gainGon amplifier boreD, viz.,G propto I/D, was obtained for flowing gas media relative to that previously observed for nonflowing gas mixtures which is consistent with the proposed mechanism of gas cooling by convection. Highest gain values obtained were 7.8 and 6.2 dB/m with the flowing gas mixtures CO2: N2: He and CO2: CO : He, respectively, in a 12 mm bore water-cooled amplifier tube. Similarities between CO2: N2and CO2: CO systems suggest that pumping of the CO2laser by resonant transfer from CO* (upsilon = 1) can be significant.     

Folded-path atmospheric-pressure CO2laser

A folded-path transversely excited atmospheric-pressure CO2laser utilizing shower or brush discharges is described. The output pulse has an initial peak 0.4 μs wide followed by a tail2-3 mus long. A peak power of 0.2 MW with 4.4 percent efficiency is obtained. By rotating one of the mirrors of the resonator the tail is eliminated, yielding a pulse 0.2 μs wide of the same peak power.