IR Laser Sources

Tunable gas-phase lasers are expensive. Less expensive solid-state diode lasers with wavelengths in the NIR are available. Commercial instruments using multiple diode lasers are available for NIR analyses of food and fuels. Because of the narrow mission lines from a laser system, laser sources are often used in dedicated applications for specific analytes. They can be ideal for process analysis and product quality control (QC), for example, but are not as flexible in their applications as a continuous source or a tunable laser. 

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Fig. 16.23. DIOS-MS spectra of bradykinin from UV and IR laser sources. Insets Expanded m/z = 1061 peak of bradykinin.

Despite the simplicity of the d configuration there is only very fittle known on the LF luminescence of d complexes. Since the ground state as well as the LF states are spin doublets the emission is a spin-allowed process. Well known is the fluorescence of Ti(III) in sapphire [14] which is used as a near IR laser source [15-18]. A few d complexes have been shown to be fluorescent as molecular systems (Fig. 1) [19,20] ... 

Successful detection of various trace gases at concentration levels typically of the order of parts per billion has been achieved with mid-IR laser sources, including lead-salt diode lasers and, more recently, QCLs. 

In IR-Vis SFG, two coherent laser beams, one visible and the other from a timable IR laser source (coj and CO2) impinge on a surface. The induced nonlinear polarization at the surface results in the coherent generation of light at the suih-frequency (0 3 = coi + CO2) [34]. The intensity of the sum-frequency light is given by... 

Operate the mid-IR laser source at a repetition rate sufficient to produce acceptable signal-to-noise ratio in the mass spectrum within the dwell time at each pixel to perform a LAESI 2D MSI experiment. (Optional) For molecular imaging in 3D, nse a spectrnm acquisition rate higher than the laser sonrce repetition rate to successfully mass analyze the ions generated within a single laser pulse. Wait for START signal to initiate ablation sequence (11). 

The application of action spectroscopy methods to obtain IR spectra of gas-phase biological molecules generally relies on the use of tunable IR laser sources. A brief overview of the various IR laser systems available is presented here. 

To measure the t/coefficients of a poled polymer sample, the Maker fringe SHG experiment [40] is frequently carried out. The experimental arrangement is shown in Fig. 26.4. A polarized laser beam from a Q-switched Nd YAG laser (A = 1.064 /u,m) or other IR laser source is employed. The fundamental laser beam at a frequency 0) passes through the poled polymer sample and an appropriate IR blocking filter. The SHG signal is selected with an interference filter at the corresponding frequency 2o), detected by a photomultiplier tube, and measured with a boxcar integrator. The SHG intensity, /(2w), can be expressed as... 

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