A frequency stabilized compact high repetition rate TEA-CO2laser

A compact atmospheric-pressure hybrid CO2laser utilizing a transverse double-discharge technique has been constructed and operated at moderate repetition rates. A pulse output energy of 80 mJ has been obtained under single-mode conditions at repetition frequencies of 100 Hz. Using the hybrid technique to obtain single-longitudinal-mode operation, we have been able to reach a 7 kHz long-term relative frequency instability between the TEA laser and a local oscillator. Measurements of the frequency sweeping during the pulse tail (chirp) are also presented along with a direct measurement of the resonant frequency pulling effect associated with the real part of the electric susceptibility of the gas. Limitations on the pulse repetition frequency for this laser configuration are also discussed.     

High repetition rate TEA CO2laser

This correspondence reports on the successful operation of a TEA CO2laser at rates up to 1000 pps with an average output power up to 65 W over long periods of time. An essential feature of the present system is a rapid gas circulation transverse to the laser axis combined with a large volume of ambient gas. It is found that decomposition of the gas is one of the major problems at high repetition rates.     

Injection locking and mode selection in TEA-CO2laser oscillators

The injection of a master oscillator signal in a high-power TEA-CO2laser is analyzed and a dynamic model is formulated to represent the interaction. Based on the competition between the injected signal and the spontaneous emission, the model describes the transient evolution of the different field amplitudes and phases together with their effect on the inversion. A study over a wide range of injection levels and detuning frequencies clearly indicates three distinct regions of operation: a spontaneous oscillation zone, a mode-selection zone, and a frequency-locking zone. The main predictions of the model are compared with the results obtained with an experimental injection apparatus that assures adequate control of the TEA laser cavity length and that provides means for measuring the frequency of the output pulse. While the first two zones are directly observed, it is experimentally established that, at injection levels up to 5 W/cm², the frequency-locking zone does not exceed, as predicted, the 3-MHz resolution limit of the apparatus.     

Pulse-forming and line-broadening in AM mode locking of the TEA-CO2laser

The present paper describes AM mode locking for homogeneously broadened systems, a procedure for measuring linewidths under laser conditions, and finally, experimental results for a 1-atm CO2laser. Working in the frequency domain, analytic solutions are given for the pulse bandwidth and pulse shape as a function of frequency detuning. We arrive at a simple expression for the maximum positional shift of the mirror distance. It turns out that the linewidth is inversely proportional to the maximum frequency shift and can be obtained independent of the modulation parameters and time constant of the pulse-signal detector. Applying this analysis to an amplitude-modulated CO2laser the pulsewidth and linewidth have been measured as a function of gas composition and modulation depth. In contrast to predictions deduced from absorption measurements under neutral conditions we find the striking result that under laser-discharge conditions the linewidth increases and the pulsewidth decreases with increasing helium percentage.     

Studies on injection locking of a TEA-CO2laser for stable high-power operation

Optimum Conditions for stable operation of an injected TEA-CO2laser with high-power output have been pursued both theoretically and experimentally. The stability of injection locking as well as the obtainable peak power was analyzed based on a transient mathematical model which deals with buildup of the electric fields. Predicted dependence of injection locking on the injection intensity, the output coupling, and the resonator length was tested and verified in the experiments.     

Frequency tuning characteristics of a Q-switched Co:MgF2laser

A tunableQ-switched Co:MgF2laser has been developed for atmospheric remote sensing applications. Frequency tuning is provided by a quartz etalon and a specially designed three-element birefringent filter covering the whole gain bandwidth of the Co : MgF2laser. The laser has good temporal and spectral characteristics, with an emission linewidth of approximately 3 GHz (0.1 cm^-1).     

Frequency modulation of a self-mode-locked dual-polarization CO2laser

Simultaneous active stabilization and frequency modulation of a mode-locked dual-polarization CO2laser is reported. Mode locking was maintained during frequency modulation through use of a self-regenerative feedback technique.     

Operational characteristics of a PIE CO2laser

The design and operational characteristics of a high power pulser-sustained CW CO2laser is described. The "photoinitiated impulse-enhanced electrically excited" structure possesses operational features similar to an "electron beam-sustained" device and as such may provide a relatively simple and inexpensive alternative in high power CO2laser design.     

Frequency shift in a line center stabilized CO2laser

A shift in frequency of 3.5 MHz from the rotational line center has been observed in a power-stabilized CO2laser operating on theP(14)line. The shift was observed during long baseline interferometry experiments and is due to gain depletion by competing rotational levels.     

改进型高重复率TEA CO2激光器特性

本文介绍了改进型高重复率小型TEA CO2激光器的结构和特性.在30Hz重复率下工作时,每脉冲输出能量达到100mJ.     

Gain characteristics of a MAGPIE coaxial CO2laser system

Gain coefficient measurements of a MAGPIE (magnetically stabilized, photoinitiated, impulse-enhanced, electrically excited) coaxial CO2laser discharge are presented. The effects of gas composition, input power, pulser ionization, and magnetic field on gain are examined. Measurements of the radial gain profile and saturation intensity are also discussed. A maximum small-signal gain of 0.30 m^-1is observed, along with a saturation intensity of 190 W/cm².     

Electrical and gain characteristics of a multiatmosphere UV-preionized CO2laser

The scaling parameters of a UV-preionized TE CO2laser which permit the direct comparison of small-signal gains as a function of laser pressure have been investigated in the pressure range of 4-19 atm. Careful measurements of the gain as a function of laser pressure in both the 9.4 and 10.4 μm vibrational bands were made under the appropriate scaling conditions. A theoretical model for the gain incorporating regular, hot band, and sequence band rotational lines, with proper account taken of non-Lorentzian line overlap effects, predicts the observed pressure dependence of the small-signal gain.     

High peak power and high repetition rate characteristics in acurrent-pulsed Q-switched CO2 laser with a mechanical shutter

An electro-mechanical Q-switched (EMQ) CO₂ laser is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (>10 kW) and high repetition rates (>1 kpps). In order to analyze the output characteristics, the peak power and the duration of the output pulses have been measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure (<4 kPa) CO₂ gas system, the standard rate equations adequately explain the experimental results by introducing a new switching function for the form of the cavity loss for the mechanical chopper. In an EMQ-laser with a high initial inversion density (4.5·10¹⁵ /cm³ at 150 mA peak current), multiple peak pulses or pulse distortion have been observed. This is due to the plasma screening effect induced by the burning of the metal shutter blades placed inside the cavity. It is found that tungsten metal shutter blades can be used up to a power density of 259 MW/cm² for a focused beam without this effect occurring, The solutions of the rate equations show that optimum coupling can prevent the plasma screening effect even for a Q-switching time longer than the pulse buildup time. The EMQ-laser configured for optimum coupling has produced a peak output power of 30 kW for the 9P20 transition branch in the CO₂ spectrum without any pulse distortion. This value has been obtained even though the discharge length was only 1.3 meters     

High-current characteristics of the continuous-wave hollow-cathode He-I2laser

Output power versus current characteristics of a multiple-anode hollow-cathode He-I2laser have been studied using quasi-continuous excitation. Oscillation has been obtained on a total of 25 transitions of I⁺ranging in wavelength from the blue to near infrared and including 9 new CW transitions. For all transitions, upper level excitation is attributed to thermal-energy charge-transfer reactions. No saturation in laser output power has been detected for increasing discharge current up to 20 A in the 75-cm-long 2.5-mm-bore device. CW power levels up to 100 mW each for strong transitions and approaching 1 W total over all transitions have been achieved.     

Gain and fluorescence characteristics of flowing CO2laser systems

Single-pass gain has been measured for flowing CO2, CO2-N2, CO2-He, CO2-N2-He, and CO2-N2-H2mixes. The gain for CO2-N2mixes varies as d^-0.9, wheredis the tube diameter. The diameter dependence of the gain is less pronounced for CO2- N2-He mixes; a peak gain of 4.7 dB/m was obtained in a 1/2 in diam tube. Fluorescence data indicate that the upper laser level population is saturated at 100 mA in all cases. The addition of He, H2, or O2depopulates the lower laser level; helium further increases the population of the upper laser level. The addition of CO increases the population of the upper laser level, probably by resonant transfer from the excited vibrational states of CO.     

A compact wide-aperture single-mode TE-CO2laser with a low chirp rate

Single mode operation of a TE-CO2laser was obtained using a2 times 2 times 30cm gain module in a Cassegrain resonator with a Gaussian reflectivity convex mirror to produce a fundamental mode of large cross sectional area, and reducing the pressure to 375 torr in a 50 cm long cavity to limit the oscillation to a single longitudinal mode. The 70 ns gain switched pulse (FWHM) had an energy of 175 mJ, a peak power of 2.0 MW, a diffraction limited far-field, and a frequency chirp rate lower than 60 kHz/μs².     

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.     

High-pressure sealed CW CO2laser with high efficiency

Discharge stabilization, long-term operation, output power characteristics, and efficiency of the high-pressure CW CO2laser have been investigated under sealed conditions. A comparison is made with low-pressure CW CO2lasers. Two types of electrode structures suitable for operations in the pressure range 100-760 torr are presented. Effects of O2and CO on the discharge stability and unsaturated gain are described. By using molecular sieve3Aas an adsorbent of water vapor, which was the most detrimental impurity, sealed operation with no decrease in output power was achieved at 0.5-1.5 kW for more than 150 h elapsed time including about 30 h of discharge time. It has been demonstrated that high efficiency can be obtained in spite of high-pressure and sealed operation. The efficiency was improved by reducing the cavity loss due to the absorption of intracavity radiation by CO2molecules in the unexcited region, and by finding the optimum of gas mixture. A maximum efficiency of 19 percent was obtained at a 1 kW power level for a 100 torr gas mixture of either CO2-CO-N2-He = 2-1-19-19 or CO2-CO-N2-He-Ar = 2-1-18-10-10. The effects of Ar and N2proportion on the unsaturated gain and saturation parameter are discussed.     

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.     

Compact, high-power FIR NH3laser pumped in a CO2laser cavity

A compact CO2-NH3FIR laser system, with an NH3laser cavity inserted in the pump CO2laser cavity, was designed. Temporally smooth and reproducible single mode NH3laser pulses with an energy of 5 mJ (20 kW peak power) were obtained at the 152 μm line when optically pumped by the injection-locked single-mode CO2laser with a pulse energy of 0.3 J.