Lasers tunable radiation, generation

Pumping is with a flashlamp, as in the case of the ruby laser, and a pulse energy of the order 1 J may be achieved. Frequency doubling (second harmonic generation) can provide tunable radiation in the 360-400 nm region. 

Tunable radiation is generated by a)xuv=4o)uY+(jOY. With the radiation of a second dye laser (Ay=216-800 nm) the six-wave mixing should cover the whole range of 58 to 72 nm. 

Several different laser techniques for generating VUV and XUV radiation are now available, and these have been discussed briefly, along with the relevant theory. Of these, harmonic generation and four-wave frequency mixing have been shown to provide coherent and monochromatic radiation which is tunable over broad regions of the spectrum, from 200 nm to 70 nm, and with limited tunability to 50 nm. While these laser-driven sources are not presently available commercially, they have been developed in several laboratories around the world, and have been used in various fields of research. 

An efficient way to generate coherent, tunable radiation in the far infrared is the difference frequency generation by mixing the output of an CO2 laser kept on a selected line with the output of a tunable CO2 waveguide laser in a MIM diode (Vol. 1, Sect. 5.8). With this technique Stark spectra of CHsOH were measured over a broad spectral range [149]. 

TABLE XII Wavelength Range (nm) of Tunable UV and VUV Radiation Generated by Stimulated Raman Scattering in H2 (Au= 4155 cm ) with Dye Lasers ... 

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]. 

Nucleotides are covered elsewhere in this volume but worthy of mention is the cyclic 3, 5 -adenosine monophosphate anion (cAMP-H) , generated in gaseous species by electrospray ionization (ESI) and stored in an ion-trap mass spectrometer. This has been investigated by mass-resolved infrared multiple photon dissociation (IRMPD) spectroscopy in the 900 1800 cm fingerprint range using the powerful and continuously-tunable radiation from a free electron laser. Further details of this IRMPD application are given in the mass spectrometry section later. 

DFG is a nonlinear optical technique in which tunable infrared radiation is generated by mixing the radiation from a fixed-frequency pump laser with that from a tunable laser source in a birefringent crystal. Typically, the fixed-frequency source is a Nd YAG laser, while the tunable radiation is generated by a dye laser (often pumped with the same Nd YAG). 

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