High-repetition-rate laser sources

Hatsis, P., Brombacher, S., Corr, J., Kovarik, P., and Volmer, D. A. (2003). Quantitative analysis of small pharmaceutical drugs using a high repetition rate laser matrix-assisted laser/ desorption ionization source. Rapid Commun. Mass Spectrom. 17 2303-2309. 

Of course, a TCSPC system works effieiently only with a high-repetition-rate excitation source. Diode lasers ean be built with any repetition rate up to about 100 MHz and are available with 375 nm, 405 nm, 440 nm, and 473 nm emission wavelength. Diode lasers are cost-effieient and ean be multiplexed at ps rates see Excitation Wavelength Multiplexing, page 87. For shorter wavelengths, frequency-doubled or frequency-tripled titanium-sapphire or neodymium-YAG lasers can be used. 

B. Agate, A.J. Kemp, C.T.A. Brown, and W. Sibbett, Efficient, high repetition-rate femtosecond blue source using a compact Cr LiSAF laser. Optics Express 10(16), 824-831 (2002). 

For the second task second harmonic generation by quartz has been proposed. The first procedure is to determine the relative intensity of SH compared with etalon, where the ratio of SH intensities is used for sorting. In the second procedure the laser source is working with a very high repetition rate and the number of pulses with SH intensity above a certain level is used as the separation criterion. Sorting using non-linear optics may be very effective, because... 

The only pieces of hardware needed for photo-CIDNP are a light source and an unmodified NMR spectrometer. Pulsed lasers are most convenient for illumination, as they allow both time-resolved experiments (when the laser flash is followed by an acquisition pulse after a variable time delay) and steady-state ones (when the laser is triggered with a high repetition rate, thus providing quasi-continuous excitation). All the examples of this work draw on the second variant. Nevertheless, they yield kinetic information about much faster processes than would be observable by direct... 

Different types of set-up have been reported in the literature. A typical transient absorption set-up with a continuum probe and subpicosecond time resolution, which can be used with laser pulses of a few hundred femtoseconds of duration, is shown in Fig. 7.15. The sample is excited by the pump pulses P. The pump flu-ence (number of photons per cm ) is set to be large enough to obtain an appreciable population of the excited state, which however can be small when an excitation source of high repetition rate is used (Ti-sapphire femtosecond lasers run at 1 kHz) because it allows fast accumulation of weak amplitude signals. With low repetition lasers (10 Hz) the excitation fluence should be dose to the saturation fluence ( l/ca, where (7 is the absorption cross section of the solute at the pump wave-... 

Nd YAG lasers (frequency multiplied to provide a 355 nm output) predominate in modern instruments because of the high repetition rates available and their long lifetimes. Nitrogen (337 nm) lasers are also used in older instruments. MALDl sources are usually coupled with TOF analyzers because of the availability of the mass range necessary to observe singly charged proteins. MALDl is an in vacuo technique, although atmospheric pressure MALDl does exist. 

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