Time-dependent processes in CO2 laser amplifiers

Abstract

Measurements have been made of the small signal gain of CO2-N2-He laser amplifiers excited either by short pulses or a 50 Hz rectified a.c. waveform. A model, based on the known vibrational energy-level scheme appropriate to this laser, is developed and applied to the data. The relaxation times of the upper and terminal laser states, the relaxation rate of the first vibrational state of nitrogen and the nitrogen to carbon dioxide energy transfer rate are determined. Gas heating which limits laser gain is described in terms of a phenomenological thermal time constant, and the value of this quantity is deduced from the a.c. data under various conditions.The data presented permits the excitation conditions for optimum amplification of pulses from a Q-switched oscillator to be determined under non-saturating conditions.

Rotational relaxation and gain saturation in CO2 laser amplifiers

“…At low powers the rate determining parameters (apart from the incident radiation) are the spontaneous relaxation rates between the vibrational levels of CO 2 involved in laser action. These rates are known from other data (see for example Crafer et al 1969). At high powers the gain will decrease rapidly with time, so the finite relaxation rates between rotational levels become significant.…”

“…For brevity in subsequent equations, it is convenient at this point to define a quantity P equal to 2I/q as a measure of the radiation intensity. Then, using Hotz and Austin's result together with a value of w~ of 1.1 x lo3 s-l (Crafer et al 1969) we obtain the numerical relationship P s-1= 100 x (radiative power density in w cm-2).…”

“…w2, w3 are the spontaneous relaxation rates of the 001 and 100 levels respectively. The values of these quantities under normal laser pressures are known (Crafer et al 1969). E is the rate of population of the 001 level due to excitation-primarily via excited nitrogen.…”

“…An analyser in front of the detector then allowed the sampling laser pulses to be detected while the detector amplifiers were not overloaded by the high-power laser pulse. No attempt was made to synchronize the two laser pulses, a photographic integration technique, similar to that used in previous work (Crafer et al 1969), being adopted.…”

Measurement of plasma electron density by the laser self-heterodyne

“…Let p ~( w , H ) and pz(w, H ) be the two refractive indices of the active medium for a particular orientation of H and let p(w) be the refractive index of the unmagnetized lasing medium, which is not a function of the state of polarization. According to Garrett (1967) the optical path length conditions for each state of polarization are where, to a first approximation, 1 f ( p , q, r ) =p+ 7T (q+2r+ 1) cos-1…”