Radiation coherent

Modern commercial lasers can produce intense beams of monochromatic, coherent radiation. The whole of the UV/visible/IR spectral range is accessible by suitable choice of laser. In mass spectrometry, this light can be used to cause ablation, direct ionization, and indirect ionization (MALDI). Ablation (often together with a secondary ionization mode) and MALDI are particularly important for examining complex, intractable solids and large polar biomolecules, respectively. 

The emitted beam of coherent radiation is narrow and can be focused into a very small area. This means that the density of radiation that can be delivered for any one pulse over a small area is very high, much higher than can be delivered by conventional light sources operating with similar power inputs. 

Abstract Optical Parametric Oscillators provide a very efficient source of tunable coherent radiation. The principle of different kinds of OPOs are described. OPOs are used in astronomy for Laser Guide Star systems, and they may be used for other nonlinear optics applications in astrophysics, such as frequency conversion or parametric amplification. 

It is well known that by inserting an optical amplifier obtained by population inversion in an optical cavity, one can realize sources of coherent radiations, namely lasers. One can operate in the same way with parametric amphfication as shown on Fig. 1. A nonlinear crystal illuminated by an input pump is inserted in an optical cavity. This cavity is represented for convenience as a ring cavity but consists usually of a linear cavity. An important difference with the laser is that there are three different fields, insfead of one, which are presenf in the amplifying medium, all these fields being able to be recycled by the cavity mirrors. One obtain thus different types of "Optical Parametric Oscillators" or OPOs. 

If the electric dipole contribution dominates in the total SH response, the macroscopic response can be related to the presence of optically nonlinear active compounds at the interface. In this case, the susceptibility tensor is the sum of the contribution of each single molecule, all of them coherently radiating. For a collection of compounds, it yields ... 

Nowadays, tunable coherent radiation has become a fundamental tool in many areas (remote sensing, isotope separation, photochemistry, etc.), with particular relevance in optical spectroscopy. 

A third way of generating continuously tunable coherent radiation uses more complicated systems based on the principle of optical parametric oscillation (and amplification). Since the gain in these systems is not originated by stimulated emission, but by means of a nonlinear frequency conversion process, we will treat them in a separate section. 

Tunable Coherent Radiation by Frequency-Mixing Techniques... 

Figure 2.23 shows the broad spectral region covered by an OPO system, using as a pump wavelength the Q-switched radiation at 355 nm from a system based on a Nd YAG laser. Coherent radiation that is tunable from 400 nm to 2 jam can be obtained from the signal and idler waves. 

Raman spectra were obtained on a Coberg PHO Raman spectrometer equipped with a Coherent Radiation Model 52B Ar laser using 800-1200 mW of power from the 488.8-nm line a small twoprism monochromator was used to remove Imck-ground plasma lines. 

Figure 6.97 Schematic illustration of energy levels in mby that are used to create a populated metastable electronic state, which can then be stimulated to emit monochromatic, coherent radiation for a laser. Reprinted, by permission, from J. F. Shackelford, Introduction to Materials Science for Engineers, 5th ed., p. 607. Copyright 2000 by Prentice-HaU, Inc.

Another revolutionary application of electronically excited molecular systems is in laser technology. Lasers are intense sources of monochromatic and coherent radiation. From their early development in 1960 they have found wide fields of application. They have provided powerful tools for the study of diverse phenomena ranging from moonquakes to picosecond processes of nonradiative decay of excitational energy in molecules. The intense and powerful beam of coherent radiation capable of concentra-... 

Once this emissive condition is established, the coherent emitted radiation is made to stimulate further emission from the excited atoms in an optical cavity in order to amplify the intensity of the phase coherent radiation. 

A continuous laser operates by continually pumping atoms or moie-cules into the excited state from which induced decay produces a continuous beam of coherent radiation. The He—Ne laser is an example of continuous system. Another mode of operation is to apply an energy pulse to the system, exciting a considerable fraction into the excited state. When all these molecules or atoms are induced to decay simultaneously, intense but exteremely short pulse of coherent radiation is emitted. The ruby laser falls in this category. 

Assembling the PEC inside the sample compartment of a spectrophotofluorometer permitted measurement of emission spectral data (200-800 nm V3 nm bandwidth). Front-surface emissive properties were recorded by inclining the photoelectrode at A/45° to both the incident Coherent Radiation CR-12 Ar ion laser beam (501.7 or 514.5 nm) and the emission detection optics. In all experiments the 3 m dia. beam was 10X expanded and masked to fill the electrode surface incident intensities were generally <10 mW/cm. Temperature of the PEC was adjusted as previously described (9). 

These advances have opened new fields of relativity-related research in two complementary directions. One is related to the advent of laser-based sources of coherent radiation in the X-UV domain, either from high harmonic generation [6], [7] or from X-ray-laser devices, [8], The imple-... 

P. Bucksbaum, N. Ceglio (Eds.), OSA Proceedings on Short Wavelength Coherent Radiation Generation and Applications, Optical Society of America, Washington D.C., 1991. 

Coherent population transfer Transfer of population from one quantum mechanical level to another using coherent radiation. The radiation may be provided by either continuous or pulsed lasers. Using the method of adiabatic passage (see STIRAP), 100% population transfer has been achieved. 

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