Parametric studies of the optogalvanic effect in a low pressure CO2 cell

Dev, Vas; Biswas, Dhruba J.; Chatterjee, U. K.

doi:10.1007/bf00330096

Cited by 3 publications

(1 citation statement)

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“…As regards CO 2 lasers, all microscopic laser-plasma processes occurring in such active mediums have been well studied [12][13][14][15], and various OG signal detection methods in DC and RF discharge tubes have been discussed in details [16][17][18][19][20][21]. Moreover, both the dependence of the OG signal phase and amplitude on the laser modulation frequency [22][23][24] and the temporal behavior of signal shapes [25][26][27] have been theoretically and experimentally studied in many previous works.As is well known, when a CW laser oscillation is modulated, for example, by a mechanical chopper, some optically induced changes will occur in the plasma temperature resulting from the interactions of the radiation with plasma components. These fluctuations are followed by some associated variations in the plasma impedance, which, in turn, create some voltage or current variations across the discharge circuit components that are generally called optovoltaic or optogalvanic variations.…”

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Noncontact optogalvanic signal detection in DC discharge CO2 lasers

et al. 2012

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A new noncontact method for detecting optogalvanic signals in DC discharge CO 2 lasers is reported. The presented technique is based on the detection of potential difference variations through a capacitor comprised of a discharge plasma column and a coaxial or parallel conductor. The obtained optogalvanic signals exhibit better responsivity and pulse shape in comparison with other conventional techniques; in addition, they are detectable as far as 3 m from a signal source.Keywords: laser optogalvanic effect, optogalvanic spectroscopy, CW CO 2 laser.Introduction. Upon the first application of lasers in optogalvanic (OG) studies [1], the laser optogalvanic effect found widespread application in various fields [2][3][4][5][6][7][8][9][10][11]. As regards CO 2 lasers, all microscopic laser-plasma processes occurring in such active mediums have been well studied [12][13][14][15], and various OG signal detection methods in DC and RF discharge tubes have been discussed in details [16][17][18][19][20][21]. Moreover, both the dependence of the OG signal phase and amplitude on the laser modulation frequency [22][23][24] and the temporal behavior of signal shapes [25][26][27] have been theoretically and experimentally studied in many previous works.As is well known, when a CW laser oscillation is modulated, for example, by a mechanical chopper, some optically induced changes will occur in the plasma temperature resulting from the interactions of the radiation with plasma components. These fluctuations are followed by some associated variations in the plasma impedance, which, in turn, create some voltage or current variations across the discharge circuit components that are generally called optovoltaic or optogalvanic variations.A majority of the laser OG studies have so far been focused on RF discharges rather than on DC ones due to some advantages of the former such as: 1) better plasma uniformity, 2) negligible plasma-tube interactions, 3) no electrode sputtering influences, and 4) wider operating pressure range. However, DC discharges have always been of interest as a useful alternative due to: 1) simplicity of discharge performance, 2) noncomplexity of the OG signal detection, and 3) a close and direct relationship between OG pulse shapes and temporal variations in irradiated plasma parameters. So, most of the spectroscopic studies requiring well-stabilized plasmas are performed using RF discharges; however, time-dependent investigations on microscopic and quantum properties of the irradiated plasmas are generally done with DC discharges.In the case of RF discharges, the main methods for the OG signal detection include picking up the laser-induced fluctuations in: a) reflected field in a power transmission line [20], b) RF field emitted by a discharge current around a tube [3], and c) plasma transverse current across a couple of transversely positioned electrodes [21]. On the other hand, in DC discharge tubes, the OG signals are always detected by a common sampler capacitor connected to a certain point of the discharge ...

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