Self locking of gas lasers

Abstract

The self locking behavior of 6328 Å He-Ne gas lasers has been investigated at various mirror separations by controlling the oscillation intensity with the aid of an intracavity modulator. The results indicate that the self-locked gas laser with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> light pulses bouncing back and forth between both the mirrors oscillates ordinarily at mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> mode interval (f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> is the fundamental axial mode interval) and exceptionally at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1f_{p}</tex> mode interval. The ordinary self locking, that is, mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> locking, easily occurs around a certain curve plotted as a function of internal oscillation power and of pulse repetition rate or oscillating mode interval regardless of the multiplicity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> . This optimum curve of self locking is related to the minimum spread of oscillating mode intervals which results from the frequency pulling, dependent on excitation level only, and from the hole repulsion, dependent on both mode intensity and oscillating mode interval. Accordingly, the repetition rate of the output laser pulse increases with the oscillation intensity on the optimum curve of self locking. The mode quenching, which is a necessary condition of mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> locking ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m \neq 1</tex> ), is associated with the axial mode interval and the effective damping constant representing half the hole width. In consequence, the mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> locking with large <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> occurs in long cavities and becomes difficult with the increase of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> . The power-dependent transition from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1f_{p}</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2f_{p}</tex> self locking is illustrated by the power-dependence of the effective damping constant. In order to realize mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> self locking, the relative positions of the discharge tube and both the mirrors must be chosen so as to make the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2m</tex> th spatial Fourier component of the excitation density predominant over the other components. The pulse repetition rate of the output light from a locked gas laser is limited mainly by the damping constant of the laser medium. For this reason, the technique of mf <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> locking is desirable rather to get high output power pulse using a long tube and cavity than to realize high speed pulse using a short tube and cavity.