HeNe laser beam

The digitized (ADC) discrete interferogram is Fourier transformed (DFT) by a PC to yield a wavenumber dependent spectrum. Sampling points are determined by the interference pattern of a monochromatic HeNe laser beam which is transferred collinearly with the IR beam. The resulting high wavenumber accuracy constitutes the third advantage of FTIR. 

Fig. 1.35 Optothermal spectroscopy of solids and of molecules adsorbed at surfaces (a) propagation of thermal wave induced by a pulsed laser (b) deformation of a surface detected by the deflection of a HeNe laser beam (c) time profile of surface temperature change following pulsed illumination [90]...

In routine FTIR spectroscopy the spectrometer is operated in continuous scan mode. In this mode of operation, the moving mirror is scanned at a constant velocity, v (cms ), with the light beam path difference at any time, t being given hy 6 = 2 1 (cm). An internal HeNe laser beam is also passed through the interferometer and, since it is essentially monochromatic (I5,798cm ), it is used to accurately calibrate the positions of Mm for data sampling. Continuous scan FTIR is most commonly used to monitor stable samples, but can also be used in rapid-scan mode to monitor time-dependent processes on timescales down to ca. 20 ms. 

A prism can be used for expansion of a laser beam if the incident beam is nearly parallel to the prism surface. Calculate the angle of incidence ot for which a HeNe laser beam X = 632.8 nm) transmitted through a 60° equilateral flint glass prism is expanded tenfold. 

A HeNe laser beam is split into a sample beam and a reference beam. The sample beam propagates via the ITO coated glass and the polymer film, and is then reflected back by the gold electrode. An AC-modulating field (about 5 kHz) was applied across the polymer film. A detector was employed to measure the modulations at two half-intensity points of a... 

Figure 10.12. Electron microscopy of freeze fractures, (a) Picture of the TGBa surface of 14P1M7 in the electron microscope, (b) Schematic drawing of the smectic blocks and the sample surface, (c) Orientation of the surface normal s with respect to the TGB structure (bottom) and the resulting pattern of the intersection lines between the surface and the smectic layers (top), (d) Experimental diffraction spots obtained for the scattering of an HeNe laser beam on the surface pattern obtained by electron microscopy. (Parts (a), (b), and (d) of this figure are reprinted from [125].)...

In 1973, Pohl, et al of the IBM Zurich Research Laboratory reported the measurement of the thermal diffusivity in NaF as a function of temperature. The grating was created by a CO2 laser and detected by its diffraction of a HeNe laser beam. The time scale was 100 /IS. They called this technique Forced Rayleigh Scattering . 

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