Laser, tunable

Subsequent to the advent of the dye laser, tunable lasers based upon other lasing media were developed which operate over various wavelength ranges. Nobable among these are the f-center lasers and diode lasers which are tunable in the infrared. 

With this technique the Doppler width could be reduced by two orders of magnitude below the natural linewidth, and spectral structures within the Doppler width could be resolved. Examples are the resolution of hyperfine structure components in an 12-beam using a single-mode argon laser (tunable within a few gigahertz) or the investigation of the upper state hfs-splitting in the atomic... 

The femtosecond fluorescence up-conversion setup has been described elsewhere [13,14]. Briefly, a second harmonic (SH) of a home-made chromium-forsterite femtosecond laser tunable from 610 to 660 nm was used to excite the sample (Fig.2) [14]. The pulse duration of the SH pulses was about 50 fs at the full width at half maximum (FWHM). We were successful in the cavity-dumping operation of this laser [14] and kept the repetition rate as low as 4 MHz. Reduction of the repetition rate was necessary to avoid multiple hits of the same location of the sample as small as possible. The excitation intensity, controlled by a neutral density filter before the sample cell, was (0.5-l)xl012 photons/cm2/pulse. Special care was taken to work at the lowest excitation light intensity so that the effect of the exciton-exciton annihilation process was negligible. 

Figure 39. OH - X II chemiluminescence from the reaction of hot H atoms with NjO under bulk conditions, (a) Shows vibrationally-resolved emission from 193 nm HBr photolysis (h) is for 220 nm HI photolysis (i.e., doubled dye laser tunable photolysis source) and lower resolution. The peaks labeled a and b were used to obtain the data shown in Figure 40.

Laser-pumped dye Depends on pump laser Tunable... 

Fig. 2.16 Saturation spectroscopy inside the cavity of a laser (a) experimental arrangement (b) output power P (co) (c) experimental detection of the Lamb peak in the output power of a HeNe laser tunable around X = 339 pm, caused by the Lamb dip of a CH4 transition in a methane cell inside the laser cavity [221]...

Particularly for polyatomic molecules with their complex visible absorption spectra, the reduction of the Doppler width is essential for the resolution of single lines [392]. This is illustrated by a section from the excitation spectrum of the SO2 molecule, excited with a single-mode frequency-doubled dye laser tunable around X = 304 nm (Fig. 4.4b). For comparison the same section of the spectrum as obtained with Doppler-limited laser spectroscopy in an SO2 cell is shown in Fig. 4.4a [391]. 

R. Kormann, H. Fischer, C. Gurk, F. Helleis, T. Kltipfel, K. Kowalski, R. Konigstedt, U. Par-chatka, V. Wagner, Application of a multi-laser tunable diode laser absorption spectrometer for atmospheric trace gas measurements at sub-ppbv levels. Spectrochim. Acta, Part A 58, 2489 (2002)... 

A particularly efficient cw vibronic laser is the emerald laser (BeaAliSiaOigtCr " ). When pumped by a 3.6-W krypton laser at Xp = 641 nm, it reaches an output power of up to 1.6 W and can be tuned between 720 and 842nm [5.131]. The slope efficiency dPout/dPin reaches 64% The erbium YAG laser, tunable around X = 2.8 p.m, has found a wide application range in medical physics. 

L.F. Mollenauer Room-temperature stable F -like center yields CW laser tunable over the 0.99—1.22 p.m range. Opt. Lett. 5, 188 (1980)... 

Contents Tunable and High Energy UV-Visible Lasers.—Tunable IR Laser Systems.—Isotope Separation and Laser Driven Chemical Reactions. -Nonlinear Excitation of Molecules.—Laser Photokinetics. Atmospheric Photochemistry and Diagnostics. Photobiology. Spectroscopic Applications of Tunable Lasers. 

Liquid dyes lasers tunable in the visible range have been known since the middle of the sixties. They are based on organic colorants dissolved in various solvents. The light absorption from the pump source brings the dye molecule to its excited singlet state, and the emission to the terminal vibrational state can then be turned by using appropriate resonant cavities to produce laser emission in the spectral range of fluorescent emission. 

Reisfeld R. Solid state lasers tunable in the visible spectrum and nonlinear materials in glasses. J. 

Unfortunately, powerful IR lasers tunable over a significant frequency range are difficult to obtain. Currently, the most effective but highly demanding approach to this end is represented by the free-electron laser (FEL). FEL facilities are limited and offer access for researchers to perform their experiments at dedicated ports on a tight schedule (Fig. 9.35). Alternatively, optical parametric oscil-lator/amplifiers (OPO/As) can serve as tunable IR light sources [139,156]. 

Versatility. IR MP processes can be observed in polyatomic molecules of any complexity and symmetry if they have more than four or five atoms and have IR absorption bands in the lasing spectral region of high-power IR lasers. Most experiments on MP excitation and MP dissociation have been carried out with CO2 lasers (A = 9-10 yum). The development of free-electron lasers tunable over a wide IR range made it possible to observe IR MPE/D of molecules when the 3 /itm C-H stretch vibrational absorption band and the 6 jam C = 0 band were acted on (Petrov et al. 1997). 

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