Harmonic generating crystals

Figure 1. Block diagram showing component layout for both the laboratory apparatus and the mobile unit Y, Nd YAG laser S and F, second and fourth harmonic generation crystals, respectively ...

Figure 6. Instrumental schematic for vacuum UV photofragmentation-laser induced fluorescence measurement of ammonia SHGC, second harmonic generation crystal SFMC, sum frequency mixing crystal BS, beam splitter BD, beam dump TP, turning prism CL, cylindrical lens R, reflector TD, trigger diode OSC, oscillator cell AMP, amplifier cell BE, beam expander G, grating OC, output coupler M, mirror BC, beam combiner L, lens A, aperture PD, photodiode SC, sample cell RC, reference cell FP, filter pack SAM.PMT, sample cell photomultiplier REF.PMT, reference cell photomultiplier PP, additional photomultiplier port EX, exhaust and CGI, calibration gas inlet to flow line. (Reproduced with permission from reference 15. Copyright 1990 Optical Society of America.)...

Figure 8.4 Principle of autocorrelation. S, second harmonic generator crystal or sample cell M, movable mirror F, filter or monochromator D photomultiplier...

Strategy and Tactics in the Search for New Harmonic-Generating Crystals... 

Optical multipass cells have been used for the enhancement of CW Raman scattering(4) however, these cells are typically not well-suited for use with high power, pulsed lasers. A new multipass cell for use with a pulsed Nd YAG laser is proposed whereby the 1.06 micron laser output is admitted into a multipass cell cavity where it is partially converted to 532nm with a Brewster s angle cut second harmonic generating crystal The 532nm pulse is trapped in the mirrored cavity while the 1.06 micron pulse is dumped. This multipass cell concept has been demonstrated with the experimental set-up shown in figure 1. 

Figure 8-3. Layout of the experimental setup for conventional pump-probe experiments. SHG second harmonic generation crystal PD photodiode OMA optical multichannel analyzer.

Fig. 1. Experimental setup of the ultrafast confocal microscope. BS1 and BS3 are 50% beam splitters, while BS2 is a dichroic beam splitter. SHG second harmonic generation crystal OBJ microscope objective PZT piezo translator PMT photomultiplier IF interference filter.

Three features of this laser source merit further discussion. First, in a typical kinetic experiment, the 1/e chemical lifetime of the photolytically produced radicals varies between 0.2 and 25 ms, a representative mean being ti/e = 2 ms. For statistical reasons, one desires to collect a minimum of 20 concentration versus time data points per 1/e concentration decay period. For multichannel scaling detection, these typical kinetic conditions imply a maximum dwell period per channel of 100 ys. The ultraviolet laser source described above emits 2.5 x 10 pulses per 100 ys interval thus, relative to chemical decays, this rapidly pulsed source is viewed by the experiment as a cw excitation probe. Second, given that a pulsed initiation/cw detection kinetics configuration is desired, one may ask why a cw laser source is not used. The rationale here is that the visible-to-ultraviolet conversion efficiency is much higher when the quasi-cw source rather than a cw source is used. Frequency doubling efficiency varies in proportion to the fundamental peak power density present in the second harmonic generation crystal,... 

How did the AND action arise Since the two inputs were 1,064 nm and 532 nm laser pulses, their simultaneous presence in an intervening third-harmonic generating crystal produced 355 nm light via frequency mixing. The light at 355 nm was absorbed by the cyclophanediene unit of 60 and it was converted to the dihydropyrene via an electrocyclic ring closure to produce 62. When the central porphyrin unit in 62 was excited by a read laser at 650 nm, PET occurred from it to the Ceo unit. Another thermal ET quickly followed from the dihydropyrene unit to the porphyrin... 

It is clear that the essential third-harmonic generating crystal brings in a bulk material component to what is otherwise a molecular-scale experiment. However, the all-optical nature of inputs, outputs and power supplies are to be applauded even though quantitative input-output homogeneity was not achieved. A related case is by Guo et al. [132] which involves PET too. 

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