Frequency-doubled dye lasers

This teclnhque can be used both to pennit the spectroscopic detection of molecules, such as H2 and HCl, whose first electronic transition lies in the vacuum ultraviolet spectral region, for which laser excitation is possible but inconvenient [ ], or molecules such as CH that do not fluoresce. With 2-photon excitation, the required wavelengdis are in the ultraviolet, conveniently generated by frequency-doubled dye lasers, rather than 1-photon excitation in the vacuum ultraviolet. Figure B2.3.17 displays 2 + 1 REMPI spectra of the HCl and DCl products, both in their v = 0 vibrational levels, from the Cl + (CHg) CD reaction [ ]. For some electronic states of HCl/DCl, both parent and fragment ions are produced, and the spectrum in figure B2.3.17 for the DCl product was recorded by monitoring mass 2 (D ions. In this case, both isotopomers (D Cl and D Cl) are detected. 

Figure 9.33 shows examples of SVLF spectra obtained by tuning a frequency-doubled dye laser to the Og absorption band of the system of pyrazine (1,4-diazabenzene)... 

Figure 11.42a shows an energy level diagram and some of the allowed lines in the v" = 0 level of X2I1 to the v = 0 level of A2S+ (Mount, 1992). Figure 11.42b shows the absorption spectrum of OH obtained using a butane flame as the source in this case. The emission of a frequency-doubled dye laser whose full width at half-maximum is 0.41 nm is also shown (Dorn et al., 1995a). The laser emission is sufficiently broad... 

The Frankfort LPA instrument (51-53) departs from both of these instruments in two principal ways it achieves the necessary path length within a 6-m folded-path cell, and it rapidly scans a narrow-band frequency-doubled dye laser across the spectral region of interest (the Qi(2) line group) in a process sometimes called differential optical absorption spectrometry (DOAS). The scanning rate is sufficient to ensure that the observed air volume is chemically and physically stationary during each scan (the baseline standard deviation is less than 2 x 10-4 for a 0.2-ms scan). The laser output is actively feedback-stabilized to provide a flat spectral baseline, and a detection limit better than 10"5 in optical density has been claimed. A summary of published LPA configurations is given in Table II. 

Zuckermann et al. [119] studied IR multiphoton dissociation (IRMPD) of RDX and HMX in a supersonic jet. A C02 laser was used for dissociation, with a pulsed frequency-doubled dye laser tuned to 280nm to excite the A 22(v = 1) X2 (v = 0) transition... 

For this reason many investigations have been carried out at low temperatures. In order to examine the excited states of the nucleic acids with lasers, frequency doubled dye lasers or NdrYAG lasers have to be used, because the nucleic acids absorb below 310 nm (Fig. 1, 2). An experimental arrangement for the observation of fluorescence in solution after excitation with a pulsed dye laser in the visible and UV down to 220 nm is shown in Fig. 7 18,44). 

DNA- and Poly-acridine orange-complexes Frequency-doubled dye laser 260-310 nm Kinds of Bases in DNA 1-step Interaction of DNA and Acridine orange, Energy Transfer Anders 841... 

Frequency doubled dye lasers with their high spectral intensity and tunability are ideal light sources to get an improved knowledge about such UV-induced effects in skin. The erythema effectiveness curve was investigated with frequency doubled pulsed dye lasers by Anders et al. 87 94 95>. 

The fluorescence and phosphorescence of quinazoline, 6-chloro-4-phenyl-and 6-chloro-l-methyl-4-phenylquinazolin-2(lH)-one were recorded in ethanol containing 1% of concentrated sulfuric acid. The luminescence of these compounds on thin-layer chromatography (TLC) plates saturated with ethanol was reported. 4-Morpholino- and 4-piperidino-6-methoxy-2-phenyl-quinazoline also have luminescent properties, and the ultraviolet fluorescence in the crystals and in hexane or benzene solution was discussed. The time and wavelength resolved emission from quinazoline vapor at low pressures was studied with a pulsed frequency double-dye laser and were compared with those of quinoxaline and cinnoline. ... 

An extremely sensitive MODR scheme, microwave optical polarization spectroscopy (MOPS), was introduced by Ernst and Torring (1982). The most important features of MOPS are that it requires respectively 100 and 10 times lower laser and microwave intensities than MODR and results in 10 times narrower lines. This means that it will be possible to take full advantage of differential power broadening effects (Section 6.5.1) and to utilize low-power, frequency-doubled dye lasers and low-power, broadly tunable microwave sources (backward wave oscillators) in order to gain access to and systematically study perturbations. 

Figure 3.5. (1+1)-REMPI TOF-MS of Si atoms obtained by tuning a frequency-doubled dye laser through the 4s

Vacuum ultraviolet photochemistry can also be studied by using near ultraviolet lasers of high intensity to excite 2-photon transitions in the parent molecule. An elegant early experiment was that of Wang and Davis which utilised a frequency-doubled dye laser at 300 nm to excite amultaneously the biphotonic dissociation of H2O (effectively at 150 nm, in the A -continuum) and the single photon (A - X) fluorescence of the resultant OH fragments found along the axis of the focussed laser beam. 

Analogous to the results in Ar, six-wave mixing in Ne should generate VUV at even shorter wavelengths. in the case of Ne the UV radiation of a frequency doubled dye laser (Ayy=282.1 nm) and of the sum frequency... 

The application of two-photon spectroscopy to molecules has brought a wealth of new insight to excited molecular states. One example is the two-photon excitation of CO in the fourth positive system A TJ Ug and of N2 in the Lyman-Birge-Hopfield system with a narrow-band pulsed frequency-doubled dye laser. Doppler-free spectra of states with excitation energies between 8-12 eV can be measured with this technique [253]. 

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]. 

Optical sideband cooling was demonstrated for Mg+ ions in a Penning trap [1227,1228] and for Ba+ ions in an RF quadrupole trap [1229]. The Mg+ ions were cooled below 0.5 K on the is Si/2- ip P3/2 transition by a frequency-doubled dye laser at X = 560.2 nm. The vibrational amplitude of the oscillating ions decreased to a few microns. With decreasing temperature the ions are therefore confined to a smaller and smaller volume around the trap center. 

Experimentally, pump resonance is achieved by tuning one of two frequency-doubled dye lasers into the A ito X n (1,0) band of OH. 

We first report on a two-laser photoionization experiment of benzene where the stepwise excitation was accomplished by frequency doubled dye lasers. The first laser pumped the molecule to a selected vibronic level of its first excited siglet state from where it was ionized... 

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