Laser Interferometer for Repetitively Pulsed Plasmas

Hooper, Edwin Bickford; Bekefi, G.

doi:10.1063/1.1707980

Cited by 22 publications

(2 citation statements)

References 24 publications

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“…A more restrictive limitation on this particular detection system will be the rate at which the energy density of the visible laser radiation can be changed inside the optical cavity. This will be affected by the Q of the cavity.9 10 This limitation can be overcome by removing the optical cavity and observing the change in the amplitude of the spontaneous emission lines. This effect has also been observed particularly on the 3418-A (3p.-1s.)…”

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Optical Mixing in the Atomic States of a He:Ne Laser

Cherrington

1967

Journal of Applied Physics

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Optical Mixing in the Atomic States of a He:Ne Laser

Cherrington

1967

Journal of Applied Physics

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“…8], could be disregarded. Very recently, Hooper and Bekefi [13] have given an optical analysis of a system consisting of a laser resonator and an external mirror. They have used the well-known surface integral …”

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Resonator Q modulation of gas lasers with an external moving mirror

1967

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The predicted central tuning dip in the modulated power output of gas lasers was observed by applying resonator Q modulation. The modulation was obtained by means of an external moving mirror. The signal shapes observed are explained for the quasistatic case.Saturation and gain of single-mode gas lasers can be studied by analysis of the modulated power output [1][2][3]. For instance, we predicted in the a.c. power output a central tuning dip which reveals the saturation more clearly than the well-known Lamb-dip. The dip we observed previously by applying excitation density modulation [1]. Here we report our observation of the modulation dip in case of resonator Q modulation obtained by reflecting the laser beam back into the resonator by means of an external moving mirror [4].If, for simplicity, we consider transmission losses only, the resonator quality Qo of a twomirror laser isHere L is the distance between the laser mirrors M 1 and M2, andR 1 and R 2 are their intensity reflectivities. The external mirror M 3 (reflectivity R3) and the nearest laser mirror M2 form a Fabry-Perot interferometer with length I. Its intensity reflectivity R can easily be derived [5][6][7]. To find the resonator quality Q with M 3 present we merely replace R 2 by R in eq.(1). The steady-state laser intensity in singlemode operation is [8]where el ---ol' -~/Q is the unsaturated net gain and fl is the saturation parameter. Eq. (2) holds for low excitation level only. We find the change in laser intensity due to the presence of M 3 in the 128 quasistatic casewhere 5 = 41rlu/c is the external phase difference. When the external moving mirror has constant velocity v along the beam direction, eq. (3) indicates that E2 is modulated at the Doppler frequency WD = 4~vv/c and that, in general, the shape of the modulation is non-sinusoidal. Sinusoidal modulation is obtained if 2(R2R3)½ << 1 +R 2R3 . The time-dependent part of EZcan then be writtenThe resonator quality can then be put into the form Q ~ Q + AQcOswDt, with (AQ/~) << 1 and U~ slightly abobe Qo" These conditions were needed in ref.3 in the general case of resonator Q modulation.We made experiments with a single-mode 1.15 tt He-Ne laser provided with plane internal mirrors [9] and with a hemispherical multimode 0.6328~t He-Ne laser (OIP type 160-G). The experimental arrangement was as described in ref. 10; R 3 was varied from 0.01 up to 0.75 by using beam splitters in the external interferometer. The output was detected through mirror M 1.At low modulation level we observed a dip in the a.c. power output, which is shown for the

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