Plasma-induced fluctuations in CO2lasers

Data giving the parametric dependence of plasma-induced fluctuations termed random noise and striation oscillations are presented for CO2lasers and compared to He-Ne devices.     

Gain of high-pressure CO2lasers

Gain formulas are shown for the 10.4- and 9.4-μm CO2bands for the high-pressure broadening case to point out a new regime of operation for this laser. Computer-simulated results of this gain are presented as a function of wavenumber, with density equivalent pressure and population inversion ratio as parameters. The results show gain curves that suggest continuously tunable lasers over the entire 9.4- and 10.4-μm bands with no rotational structure.     

Gain of high-pressure CO2lasers

Previous theories of high-pressure CO2gain spectra have been modified to include gain Contributions from the newly discovered 00°2 and 00°3 sequence bands. It is shown that the inclusion of these bands has important consequences for TE CO2lasers. At a pressure of 14 atm, the sequence bands typically cause a 40 percent increase in calculated gain at all frequencies. Even at pressures as low as 1 atm, the presence of the sequence lines leads to anomalous gain coefficients on many of the regular 00°1 laser lines.     

Rotational level competition in CO2lasers

Competition effects between rotational levels of the rotation-vibration band of CO2at 10.6 μ have been investigated in both traveling-wave and standing-wave CO2lasers operated in a single mode and single frequency. In a ring laser, Doppler shift and gain proportionality as a function of gas flow can be used to generate a gain anisotropy as a function of frequency so that the ring laser operates as a unidirectional oscillator. Over a narrow frequency interval, two rotational levels can be made to oscillate with oppositely directed traveling waves with an intensity crossover between the two Doppler centers. In this way, a discriminant can be derived that allows frequency stabilization to 5 parts in 10¹²in frequency. In standing-wave lasers of high-frequency stability, the rotational level competition can be observed by synchronous detection of a low-frequency variation of the heterodyne beat frequency signal of two lasers. The competition effects are due to intensity-dependent anomalous dispersion arising from saturation.     

Review of CW high-power CO2lasers

Various forms of CO2lasers have achieved CW powers in the 60-kW range, operating efficiencies approaching 30 percent, pulse energies of approximately 2000 J, pulsewidths less than 1 ns, peak pulse powers in excess of 10⁹W, a frequency stability of a few parts in 10¹², and sealed-off tube lifetimes of many thousands of hours. In addition, the laser can be easily Q-switched as well as gain-switched and has been electrically, optically, gas-dynamically, and chemically pumped. In addition to all these attributes, the CO2laser output wavelength lies within one of the best atmospheric windows. It should be no surprise then that during the last eight years, the CO2laser has firmly established itself as a candidate for recognition as the most important among the numerous laser devices presently known. Depending on the gas pressure, gas flow rate, pumping mechanisms, gas mixture, etc., CO2lasers can exhibit a wide range of noise, bandwidth, gain, and power saturation characteristics. This flexibility enables a designer to optimize the performance of CO2laser stable-frequency master oscillators; power oscillators; low-noise high-gain preamplifiers; intermediate-power or high-power amplifiers. As a result, CO2laser oscillator-amplifier chains can be designed utilizing guidelines similar to those which have been extensively applied in the design of transmitters in the RF and microwave region of the electromagnetic spectrum.     

Characteristics of sealed-off waveguide CO2lasers

Gain and output power of sealed-off waveguide CO2lasers are presented as a function of gas mixtures and total gas pressure. Experimental data on circular-bore and square-channel waveguide lasers are presented. Output power per unit length of 0.2 W/cm is achieved for both types of lasers in agreement with gas-discharge scaling laws which are presented. Saturation intensities as high as 24 kW/cm²are inferred from the data. The effects of the optical properties of the waveguide wall material on the waveguide losses are discussed and theoretical waveguide loss versus wavelength is presented for BeO, Al2O3, and fused silica.     

Photon-drag Ge detectors for CO2lasers

Photon-drag effect in p-type germanium provides simple detectors for CO2lasers. Design parameters of these detectors for various applications are discussed.     

Role of helium in TEA CO2lasers

The role of helium in TEA CO2lasers differs from that in low-pressure CO2lasers. TE CO2laser output is nearly proportional to the gain-bandwidth product, and, at a total pressure of 250 torr, it is independent of whether helium is present or not. Above 250 torr, the laser could not be operated without helium.     

Mechanism of passiveQswitching in CO2lasers

PassiveQswitching of a CO2laser by saturable absorbers is analyzed in terms of a four-state kinetic model previously used to interpret infrared saturations double resonance, and pulse transmission. Good agreement is found between the predictions of this model and the experimental dependence of such variables as pulsewidth, repetition frequency, and peak power on the presence of buffer gases mixed in with the absorber.     

Properties of high-energy electrically pulsed CO2lasers

The output properties of an electrically pulsed CO2laser have been investigated as a function of partial gas pressure and discharge voltage. The output pulse became sharper with increasing CO2pressure. The output pulse energy increased with increasing helium pressure up to a pressure where the output became independent of further increases. Output pulses of 24 joules at 3.6 MW and 3.6 percent efficiency were obtained at 1/10 atmosphere in a 3.5-meter-long 5-cm-bore laser tube.     

Life and parameter studies on sealed CO2lasers

The life and power outputs of sealed CO2lasers with xenon and hydrogen additives have been investigated. The results confirm the usefulness of hydrogen for achieving long life, but suggest that the power increases previously observed with the addition of hydrogen may be due to changes in CO2concentration rather than to relaxation effects.     

Photon-drag germanium detectors for CW CO2lasers

CW CO2laser radiation is detected by employing the photon-drag effect in a p-type germanium bar. Design, fabrication, and performance of such detectors are discussed.     

4B1--Recent developments in CO2lasers

Experimental results are presented showing the effect of tube diameter on the output power and efficiency of CO2lasers. It is shown that both output power and efficiency are almost independent of diameter over the range 11mm to 44mm. The measured values of the output power and efficiency are 75 watts per meter and 10 percent. Higher efficiencies are obtained at lower power outputs. Mirror damage is discussed and two experiments involving the irradiation of CO2and ammonia with a high power laser beam are mentioned. An explanation is given for the strong interaction between the laser beam and the discharge tube current. Finally, the flow calorimeter used to measure high power laser beams is described.     

Effects of time-delayed amplification in TEA CO2lasers

A novel technique is reported for studying the behavior of the time-dependent gain in a TEA CO2amplifier. The method involves the incorporation of an additional amplifier tube into a laser cavity already containing a laser gain tube. The two tubes are independently operated, but so arranged that they can be fired with a controllable time delay between the discharge current pulses. This system permits effects of the additional gain tube on the lasing properties to be investigated as the time delay is varied. In particular, there is a time delay between the discharge current pulse of the laser tube and the onset of lasing. The variations in this delay produced by the firing of the additional amplifier tube have been investigated. The observed time-delay changes can be related to a simple theory for the time-dependent gain. The analysis of the measurements can be used to determine parameters describing the time-dependent gain. This method has been used to measure decay times of the gain for various gas mixtures. The techniques reported here can also be used to study other time-dependent effects within laser amplifiers.