Tunable coherent radiation

Synchronously Pumped Optical Parametric Oscillator. Optical parametric oscillators (OPOs) were first used in the mid-1960s as an alternative to dye lasers for generating coherent radiation tunable over a wide wavelength region [204, 205]. It is only recently, however, that OPOs have become a practical reality with the advent of new high-quality, nonlinear optical materials and high-power, mode-locked pump sources [206-211]. 

This is an alternative solution to a tunable laser source in the optical frequency range. Here a powerful single frequency radiation (pump) is parametrically converted into equally powerful coherent radiation tunable over a wide optical frequency range (signal and idler). In its simplest version, which is also the most useful one, it is based on the optical parametric amplification of noise photons of frequencies (Wj and 0)2 provided by the dissociation of a pump photon of frequency o)p such that 0) = 0) + 0D2, the selection of a particular frequency pair being made through the phase-matching condition... 

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. 

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. 

CO2 laser A continuous or pulsed source of coherent radiation normally tunable through the CO2 vibration-rotation band centered near 10.6 pm. 

In 1970 the first report of the molecular hydrogen laser opened up a decade of activity in VUV laser development, which included the appearance of rare gas excimer and exciplex lasers and the achievement of tunable coherent radiation in the Lyman-a region via harmonic generation. The surge of activity in the development of VUV lasers arose in part from the uniqueness of the VUV region, in part from the ultimate interest in X-ray lasers and, from our perspective, from the exciting prospects in spectroscopy and molecular dynamics promised by narrow linewidth, tunable, high-power VUV laser pulses for state-selective studies. Here we review the principles on which VUV lasers are based. 

ABSTRACT. Tunable coherent radiation in the ultraviolet and vacuum ultraviolet has been generated by stimulated Raman scattering, by anti-Stokes Raman lasers, and by frequency mixing processes in nonlinear media. The theory and experimental progress in the development of these laser-driven sources is reviewed, and examples of available systems and their characteristics are discussed. Various applications in spectroscopy of radiation tunable in the wavelength region 200-90 nm are presented. 

In several regards laser absorption spectroscopy corresponds to microwave spectroscopy, where klystrons or carcinotrons instead of lasers represent tunable coherent radiation sources. Laser spectroscopy transfers many of the techniques and advantages of microwave spectroscopy to the infrared, visible, and ultraviolet spectral ranges. 

There is another important application of stimulated Raman scattering in the field of Raman lasers. With a tunable pump laser at the frequency col, intense coherent radiation sources at frequencies col =1= < v ( = 1,2, 3,...) can be realized that cover the UV and infrared spectral range if visible pump lasers are used (Vol. 1, Sect. 5.8). 

A third possibility for generating coherent radiation with tunable wavelength uses the principle of optical frequency mixing, which is discussed in Sect. 5.8. 

Similar to the induced Raman effect, the hyper-Raman effect can also be used to generate coherent radiation in spectral ranges where no intense lasers exist. One example is the generation of tunable radiation around 16 xm by the stimulated hyper-Raman effect in strontium vapor [8.69]. 

F.B. Dunnings, F.K. Tittle, R.F. Stebbings The generation of tunable coherent radiation in the wavelength range 230 to 300 nm using lithium formate monohydride. Opt. Commun. 7, 181 (1973)... 

V. Wilke, W. Schmidt Tunable coherent radiation source covering a spectral range from 185 to 880 nm. Appl. Phys. 18, 177 (1979)... 

UV/visible/NlR semiconductor diode lasers (DLs) as sources of tunable narrowband resonance radiation have been discussed in Section 22.2.2. The practical and technical advantages of visible/ NIR DLs are ease of operation, small size, room-temperature operation, and low price. In comparison with hollow cathode lamps (HCLs), they have such advantages as high spectral power, spatial coherence, and tunability. Owing to these features, detection limits, dynamic range, and selectivity of analysis are all significantly improved. 

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