Tunable Sources

In order to achieve a reasonable signal strength from the nonlinear response of approximately one atomic monolayer at an interface, a laser source with high peak power is generally required. Conuuon sources include Q-switched ( 10 ns pulsewidth) and mode-locked ( 100 ps) Nd YAG lasers, and mode-locked ( 10 fs-1 ps) Ti sapphire lasers. Broadly tunable sources have traditionally been based on dye lasers. More recently, optical parametric oscillator/amplifier (OPO/OPA) systems are coming into widespread use for tunable sources of both visible and infrared radiation. 

Absorption spectroscopy records depletion by the sample of radiant energy from a continuous or frequency-tunable source, at resonance frequencies that are characteristic of various energy levels ia atoms or molecules. The basic law of absorption, credited to Bouguer-Lambert-Beer, states that ia terms of the iacident, Jq, and transmitted, light iatensities, the absorbance, M (or transmittance, T), is given by equation 1 ... 

From an experimental viewpoint, Thomson scattering has been recently observed by using electron beams from a LIN AC [91] as well as from a laser-plasma source based on LWFA [92]. This latter observation, in particular, allows the availability of table-top, tunable sources of X/7-rays to be foreseen. 

The monochromaticity of laser beams from a tunable source permits selective photochemistry, even isotopically selective ones. For example,... 

Here we present results of high-field tunable-frequency ESR studies of CuGe03, which were done at the National High Magnetic Field Laboratory, Tallahassee, FL. A key feature of the employed technique is a combination of a 25 T high homogeneity resistive magnet and a set of easily-tunable sources of mm- and submm- wave radiation, Backward Wave Oscillators. 

This tunable source was used to investigate the transient absorption kinetics of hypericin in DMSO as a function of pump wavelength (Fig. 1.10). The startling result is that using pump wavelengths from 495 to 600 nm, the data can be fit globally by a sum of two exponentials, which except for two traces exhibits the 10-ps component characteristic of H-atom transfer. Fit results are compiled in Table 1.1. 

VES requires a tunable source of infrared pulses. In the experiments presented below, vibrational echo spectra were taken using the Stanford FEL employing the same experimental setup used to perform the vibrational echo decay experiments discussed above (16). 

One other potential analytical use of GDs is as tunable plasma sources. Tunable sources can be operated in two modes to detect either atoms or molecules of (mainly) organic... 

In classical optical absorption measurements, the absorption of a sample under different conditions as a function of the energy of the incident electromagnetic radiation is studied. This can be achieved in two ways one can either take a broadband source and use a spectrometer to disperse the electromagnetic spectrum, or use a monochromatic tunable source. There is also a... 

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