Laser colinear

The photolytic and probe pulses are colinear when they reach the sample. The photolytic pulse produces excited states and photofragments, and the probe pulse which follows closely behind must be used to analyse the concentration and/or the chemical nature of the transients. The major detection processes are known as laser-induced fluorescence (LIF) and multiphoton ionization (MPI). Transient absorptions can also be used in some cases, and this is similar to ps spectroscopy. 

In this arrangement the pulse and probe beams are colinear the probe beam is generated by a CW laser, and it falls on the photomultiplier tube D through a pinhole PH. When the thermal lens is formed in C, the divergence of the probe beam increases and the intensity seen by the detector D decreases. 

Figure 5. Current overall optical layout for laser velocimetry and Raman scattering diagnostics, shown here on new fan-induced square-cross-section movable combustion tunnel. Note the co-linear Raman and LV probe laser source axes and the colinear detection optics.

In the case of the 1S-3S transition in hydrogen and for an estimated velocity of v=3km/s, the shift is Av =l4A kHz. We can t measure the velocity distribution by observing the Doppler broadened 1S-2P transition at 121 nm with a colinear laser beam, because the production of Lyman-a radiation is very difficult. In 1991 a method to compensate or at least to measure this effect was proposed by F. Biraben [7]. The basic idea is to apply a transverse magnetic field B in the atom-laser interaction region. This field has two effects ... 

Several other types of filters are discussed by Chase (5, 7). Filters are also necessary to remove the optical output of the He-Ne laser (used for referencing) because the laser has optical axes colinear with the main laser source. Since the detectors used in FT-Raman are sensitive to the He-Ne wavelength, the laser is a source of interference. Here, plasma emission filters can be used. The white light of the instrument is filtered with a near-IR cutoff filter. A final filter may be used in front of the detector. 

Figure 6.4. Two variations of the 180° sampling geometry. The laser beam is inserted colinearly with the collection axis by a small mirror, M.

Because of the inelastic collisions with electrons, the metastable atomic beam is tilted with an angle of 20°, with respect to the incident atomic beam. The tilting from the incident beam is used to make the metastable beam colinear with the Laser beams. This colinear geometry... 

Figure 3 Typical experimental PA and PT arrangements used for gas monitoring with tunable laser sources. (A) PA detection with conventional microphone in resonant gas cell for modulated cw radiation or in nonresonant cell for pulsed radiation. (B) Noncontact refractive index sensing schemes with displaced colinear or transverse probe beam (PA deflection, 1), thermal lensing (2), or colinear probe beam (PT deflection, 3).

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