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Mode selection in a TEA-CO2 laser cavity through the use of injection techniques provides high peak power single-longitudinal-mode (SLM) pulses with relatively low intensities of injected radiation. Provided the selected mode is near the center of the pressure-broadened TEA-CO2 gain transition, and the frequency proximity requirements are met, as little as 10 μW of injected power is sufficient to effectively produce a single-frequency pulse with peak power of several MW [1]. However, if tunable pulses are desired, the requirements for mode selection as the frequency of the injected radiation is tuned away from the CO2 transition center frequency become more demanding. An analytical treatment of the coupled rate equation for the molecular population densities and for the photon densities yields an expression for the "mode selection time", or the time during which the photon flux in the favored mode is a large fraction (e.g., >90%) of the total photon flux [2]. This expression is valid for values of molecular resonance detuning smaller than the pressure-broadened halfwidth (ΔνL) of the transition. |
