Determination of the saturation parameter of a cw CO2 gasdynamic laser
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Abstract:
The saturation parameter of a cw CO2 gasdynamic laser was calculated from consecutive measurements of output power and small-signal gain performed at the same experimental conditions. The measurement of small-signal gain was made as a function of the of the H2O concentration in the laser gas; measurements of output power were done as a function of the H2O concentration in the laser gas and as a function of laser-cavity diffraction loss which was varied by changing the diameter of an aperture placed in the laser cavity. Saturation parameters obtained by both methods coincide with each other, Is=3.0 kW/cm2. This value is insensitive to the H2O concentration and this behavior is qualitatively explained by a two-level model.Keywords:
Saturation (graph theory)
Gas laser
Aperture (computer memory)
Self-pulsation
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The saturation parameter of a cw CO2 gasdynamic laser was calculated from consecutive measurements of output power and small-signal gain performed at the same experimental conditions. The measurement of small-signal gain was made as a function of the of the H2O concentration in the laser gas; measurements of output power were done as a function of the H2O concentration in the laser gas and as a function of laser-cavity diffraction loss which was varied by changing the diameter of an aperture placed in the laser cavity. Saturation parameters obtained by both methods coincide with each other, Is=3.0 kW/cm2. This value is insensitive to the H2O concentration and this behavior is qualitatively explained by a two-level model.
Saturation (graph theory)
Gas laser
Aperture (computer memory)
Self-pulsation
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Experimental verification has been obtained for a theory governing the output power of high-gain laser oscillators and a procedure is described for determining the saturation power of high-gain gas lasers. The experiments were conducted using a 3.51-μ xenon laser.
Saturation (graph theory)
Self-pulsation
Gain
Gas laser
Power gain
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A typical self-mode-locked vertical-external-cavity surface-emitting laser must operate at the edge of the stable region of the resonant cavity. Its minimal pump spot on the gain chip is used as a soft aperture. By comparing with a continuous-wave (CW) laser, the pulsed laser is focused more tightly on the gain chip due to the Kerr-lens effect. This mitigates cavity loss of the pulsed laser in comparison with the CW laser, such that successive mode-locking can be initiated. The disadvantage of the above method is that the relatively small pump spot, producing relatively large thermal effect, limits the output power of the laser. To address this issue, we propose another method with the work point of the laser moved slightly from the edge of the stable region and the pump spot moderately extended, with a spot of the pulsed laser on the gain chip that could be smaller or larger than that of the CW laser. We achieve stable self-mode-locking with a record average output power of 8.18 W in a V-type resonator, limited by the applied pump power. The pulse repetition rate and width are 0.71 GHz and 1.92 ps, respectively, and the corresponding peak power is 5.6 kW.
Self-pulsation
Optical cavity
Mode-Locking
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The paper presents investigation results on amplification and generation in supersonic flow of laser medium, flowing along laser axis, namely: 1. Opportunity to suppress laser amplifier self-oscillation and to increase maximum permissible gain is demonstrated. 2. It is shown that in supersonic flow medium splitting of gain line takes place and for that reason oscillation is double frequency in a flat resonator laser and single-frequency in each direction in a ring laser. 3. The efficiency of flowing medium laser as a master oscillator for high power lasers with phase conjugation mirror is demonstrated.
Self-pulsation
Gain
Oscillation (cell signaling)
Gas laser
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The power and gain capabilities of a CO2 laser are dependent upon the saturation intensity of the laser media. Saturation intensities reported in the literature range from 22 to 100 W/cm2 for seemingly similar laser discharge tube bores, currents, gas flow rates, and gas mixtures. Measurements of saturation intensities between 7.5 and 57 W/cm2 in a CO2 laser amplifier indicate that this parameter is inversely related to the radius of the amplified beam. A significant increase in saturation intensity for small beam radii is attributed to diffusion of excited CO2 molecules into the beam. The experimental results are in qualitative agreement with a simplified derivation of a relation governing the saturation intensity which includes molecular diffusion. This effect can result in a serious overestimate of the capabilities of a large beam laser system designed with saturation intensities obtained from small diameter probe beams.
Saturation (graph theory)
Gas laser
Intensity
Molecular beam
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Laser output power characteristics of the combustion-driven CO2 Gasdynamic Laser (CO2GDL) are presented. Laser extraction is carried out with supersonic nozzle of circular-circular (CC) and shock free (SF), which has common area-ratio (A/A*=20) and various expansion length (CC nozzle with expansion length of 30mm and SF nozzle of 45, 33, 20mm). In laser output power measurements, maximum power of 24.5W is obtained at CC 20 nazzle of expansion length of 30mm, which has maximum small-signal gain of 0.5m-1. However, at SF nozzle which has small-signal gain of 0.2-0.3 m-1, laser output power can not be obtained. Investigation of the laser excitation condition suggests that the system requires the threshold value for small-signal gain over 0.23m-1. It is concluded that, with these results a feasible laser excitation system by the CO2GDL with CC nozzle has been established. Increase of small-signal gain, extension of cavity width and selection of most suitable laser light resonator will provide a radiative heating simulator for thermal protection research.
Self-pulsation
SIGNAL (programming language)
Gain
Maximum power principle
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The gain saturation of a 337 μm HCN laser is shown to be homogeneous. Dependence of gain and saturation intensity on tube radius and gas temperature leads to the design of a compact, clean running laser.
Saturation (graph theory)
Gain
Self-pulsation
Gas-filled tube
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A laser output power control system which has an ability to realize high stability of the laser output power in long-term operation is proposed for high-power rare-gas halide excimer lasers. The system has a function of maintaining laser gas conditions, mainly the halogen gas concentration, constant against the gas degradation in the laser tube. As a result the laser output power is stabilized at near maximum available power. The system has been applied to a 20-W UV-preionozed XeCl excimer laser and the laser output power has been stabilized for 8 hours successfully with a fluctuation less than +/- 2% at 20 W.
Gas laser
Excimer
Buffer gas
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An approximate method for the analysis of the nonlinear operation of a planar circular-grating distributed Bragg reflector laser is presented. The analysis is based upon vector-wave self-consistent coupled-mode equations modified to take into account gain saturation effects. With the help of an energy theorem and threshold field approximation, an approximate formula relating small-signal gain to the output power and laser parameters is derived. The laser characteristics obtained reveal behavior of the optimal coupling strength of the Bragg reflector, which provides maximal power efficiency as a function of the laser parameters. It is also shown that the gain saturation effect provides mode selectivity in the laser structure.
Self-pulsation
Saturation (graph theory)
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Saturation (graph theory)
Gain
Self-pulsation
Gas laser
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