Laser monitoring light source

For all production methods and especially for direct photolytic methods, care needs to be taken so that the radicals are generated, or rapidly converted, into a thermal distribution as relaxation of electronic or vibrational states into the monitored ground state would complicate the kinetics. The advantages of pulsed lasers as light sources are well documented [9]. 

Figure 10. The T-jump signal for the cytochrome-c/iron hexacyanide couple. The vertical scale is approximately 10-5 V/V full scale. Approximately 10s laser shots where averaged for this trace, with a Hg-Xe lamp as the monitoring light source.

Miniaturization Application of lasers as light sources resulted in a reduction in the size of refractive index detectors and made them compatible with in-line monitoring systems that are needed in capillary separation technology. The refractive index of minute amounts of solution may be determined by the measurement of the diffraction phenomenon produced in the interaction between the laser beam and a fluid-filled capillary. The laser beam passing through an off-center capillary produces a fan of scattered light in the plane perpendicular to the tube axis. The position of a single line corresponds to the refractive index of the fluid within the tube... 

The flash photolysis method was first developed by Norrish and Porter (1) and has made a great contribution to the fields of chemical reaction and relaxation phenomena. Its temporal resolution has been improved from ys to tens of fs by introducing pulsed lasers as excitation and monitoring light sources. The dynamic behavior of unstable radicals and molecular triplet states was the main subject of concern for studies in the ys time range. Ns laser flash photolysis made it possible to observe dynamics of excited singlet S] )... 

For the visible and near-ultraviolet portions of the spectmm, tunable dye lasers have commonly been used as the light source, although they are being replaced in many appHcation by tunable soHd-state lasers, eg, titanium-doped sapphire. Optical parametric oscillators are also developing as useful spectroscopic sources. In the infrared, tunable laser semiconductor diodes have been employed. The tunable diode lasers which contain lead salts have been employed for remote monitoring of poUutant species. Needs for infrared spectroscopy provide an impetus for continued development of tunable infrared lasers (see Infrared technology and RAMAN spectroscopy). 

Pulsed lasers emit pulses so short that even the fastest photoprocesses can be monitored, which would be impossible using conventional light sources. 

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