Optogalvanic Effect
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Neon Discharge




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Optogalvanic set-up at ISP

Our high resolution optogalvanic set-up consist of a ring dye laser which is capable of operating in single mode with very narrow line width. The ring dye laser is pumped using a high power intensity stabilised Argon ion laser. The output beam of the ring dye laser is modulated using a mechanical chopper and allow to pass through the gas discharge produced in a gas discharge tube or hollow cathode lamp. Laser pulses from an Nd:YAG laser (532 nm) can also be used as a source. The discharge is produced by applying a high voltage using a highly regulated ripple free dc power supply. A current limiting resistance and a milli ammeter is connected in series with the cell. The modulated optogalvanic signal is detected by blocking the dc voltage using a coupling capacitor. The amplitude of the signal is measured using a digital storage oscilloscope and the phase of the signal is measured using a lock-in-amplifier. Another lock-in-analyser can be used to record the signal near the instability region of the discharge. 

Optogalvanic Set-up


Photoemission Optogalvanic Studies

If we keep one of the electrode of a discharge cell as the target electrode for arradiation with a laser beam, then the impedance of a discharge can be changed through photoelectric emission. This impedance change due to photoelectric emission in the presence of a discharge is known as the photoemission optogalvanic (POG) effect. The POG effect is analogous to the optogalvanic effect, but the optogalvanic effect is a resonant phenomena while the POG is a nonresonant one. The study of POG effect is an effective methode for the understanding of the properties of discharge plasma and for the surface characterization of the target electrode. We have used pulsed laser beams to investigate POG effect in number of metals like copper, silver and gold by using these as electrode materials . Multiphoton induced POG effect has been found to take place when these materials are used as irradiated electrodes in a discharge tube. POG effect near the instability region of a hollow cathode discharge has also been investigated . Characteristic features of chaotic phenomena has been observed with laser irradiation of the discharge.
POG Studies on Copper
Optogalvanic Studies
Tunable lasers are excellent light sources to induce optogalvanic effect. When the wavelength of a laser beam passing through an electrical discharge is finely tuned, perceptible changes in the impedance takes place corresponding exactly to those wavelengths which are able to induce transitions between the energy levels of the various atomic, ionic or molecular species in the discharge. Thus one can get an optogalvanic spectrum by monitoring the discharge current as a function of wavelength. With the help of a tunable ring dye laser capable of operating in single mode with very narrow linewidth (<5 MHz), we have successfully carried out high resolution OG studies in various gas discharges. Notable among these is the high-resolution spectroscopic study of nitrogen discharge. The N2 rotational spectrum of band in the first positive system of N2 molecule has been recorded using OG technique and assignment of 432 rotational levels belonging to the 27 branches of this band has been carried out. Also pressure broadening effect has been studied by measuring the linewidth of Ne emission line using optogalvanic effect. In another experiment modification of spectral characteristics and optogalvanic response in Ne hollow cathode under laser excitation has been investigated.

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