Spectroscopy opto-galvanic

In the previous section we described how optical resonance could be detected by direct observation of electrical phenomena. From this point of view we described a special type of opto-galvanic spectroscopy. When electrical detection of optical resonance in connection with measurements on electrical discharges or flames is performed the term Laser-Enhanced Ionization (LEI) spectroscopy is frequently used. In Fig.9.9 opto-galvanic spectroscopy (LEI) on a gas discharge is illustrated. The laser beam is directed into the discharge and when it is tuned to an optical transition the discharge current is changed, since the probability of collisional ionization is different for 

Opto-galvanic spectroscopy of flames has important analytical applications. If an atomic absorption flame (Sect.6.5.3) is irradiated by a tunable laser a change in the current between two electrodes, placed in the outer parts of the flame, can be detected. A typical arrangement is shown in Fig. 9.10. A sensitivity exceeding that obtainable in atomic absorption spectroscopy (Sect.6.5.2) can be achieved for elements seeded into the flame. Two-step excitation improves both sensitivity and background rejection. The opto-galvanic technique can also be used for studying normal flame constituents such as O, H and OH [9.60]. 

As we have seen, collisions are important for the signal generation in LEI. In low-pressure experiments photoionization instead is the principal origin of the signal. The term Resonance Ionization Spectroscopy (RIS) is then frequently used. Several examples of opto-galvanic detection schemes for different atoms are shown in Fig.9.11. If multi-photon excitation of the atoms to be studied is used the technique is referred to as REMPI (REsonance Multi-Photon Ionization) spectroscopy. The selectivity of RIS and REMPI can be further enhanced by using a mass spectrometer to ana- 

As we have seen, collisions are important for the signal generation in LEI. In low-pressure experiments photoionization instead is the principal origin of the signal. The term Resonance Ionization SpectToscojjy (RIS) is then frequently used. Several examples of opto-galvanic detection schemes 

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Opto-galvanic spectroscopy detects the absorption spectra of atoms (6) and some molecules (7) in a flame by measuring current changes induced by optical irradiation at a wavelength corresponding to an electronic transition. Two steps are involved ... 

Fig.9.9. Experimental arrangement for opto-galvanic spectroscopy on a gas discharge [9.57] and a recorded spectrum for a Ne discharge [9.1]...

Fig.9.46. Experimental arrangements for intermodulated fluorescence spectroscopy (left) and intermodulated opto-galvanic spectroscopy (right) [9.178]...

Fig.6.24. Experimental arrangement of opto-galvanic spectroscopy in a hollow cathode lamp...

K.C. Smith, P.K. Schenck Opto galvanic spectroscopy of a neon discharge. Chem. Phys. Lett. 55, 466 (1978)... 

CARS Coherent anti-Stokes Raman scattering OG Opto-galvanic [effect, spectroscopy]... 

Returning to the field of saturation spectroscopy we note, that it is also possible to observe Doppler-free saturation signals in cell experiments without detecting the intensities of the transmitted beams. Fluorescence, opto-galvanic and opto-acoustic detection can all be used. However, since the... 

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