Lasers excimer-pumped

A nitrogen or excimer pumped dye laser has been used as the excitation source. To avoid unwanted photochemical effects, the laser pulse energy used for scattering has been less than 0.5 mJ. The Van de Graaff accelerator and laser are triggered externally... 

Figure 2. Resonance Raman spectrum of phenoxyl radical excited at 399 nm (excimer-pumped dye laser), 0.5 ps after the electron pulse. Radical concentration is approximately 10 4 M. The S/N ratio for the 1505-cm band is better than 50/1.

The laser system used in the experiments consist of two excimer-pumped dye lasers. The dye lasers can produce narrow bandwidth laser radiation of wavelengths between 340 and 850 nm, which can be extended, with the use of second harmonic generation, down to 205 nm. The bandwidth is nominally about 5 GHz, but this can be reduced to 1 GHz by use of an intra cavity etalon. The energy resolution in the present experiments is limited solely by the linewidth of the laser. The maximum pulse energy is typically a few mJ in the visible wavelength region and a few hundred jiJ in the UV, after doubling. The laser intensity is measured after the... 

A. Andreoni (1987). Two-step photoactivation of hematoporphyrin by excimer-pumped dye-laser pulses. J. Photochem. PhotobioL B, 1, 181-193. 

In a later experiment the laser was replaced by a cw ring dye laser, the output of which was amplified in four stages, using a XeCl excimer laser as pump. In this way the cw output (30 60 mW) at 486 nm was amplified into 25 mJ, 10 ns pulses with a repetition rate of 50 s . In addition in this later experiment the frequency of the transition was determined with respect to the saturated spectrum of Tc2, a line of which lies within 50 MHz of half the 1 S- 2 S energy interval. Furthermore, an acousto-optic modulator was used to create a laser sideband at 50 MHz higher than the fundamental frequency so that each Tea absorption line consisted of 3 peaks, at vo, vo + 50 MHz and Vo + 25 MHz, the cross-over resonance. 

The most common pump system for pulsed CARS experiments are two dye lasers pumped by the same pump laser (N2 laser, excimer laser, or frequency-doubled Nd YAG laser). This system is very flexible because both frequencies co and C02... 

The first lasing of a rare gas-halide (RGH) excimer (XeBr) was reported by Searles and Hart in 1975. Shortly thereafter, lasing from XeF was reported by Brau and Ewing. Both XeBr and XeF lasers were pumped by intense electron beams. Excimers shown in Table I were reported to lase. In addition to electron-beam pumping, researchers have also employed volume-uniform avalanche discharges with X-ray, UV, or corona preionizations, electron-beam controlled discharges, and proton beams successfully to pump a variety of excimer lasers. 

Resonance enhanced two-photon ionization via the A <— X y(O-O) and v(l-l) bands was used for state-specific detection of NO. Frequency doubling the output of a XeCl excimer pumped dye laser in a potassium pentaborate crystal produced tunable ultraviolet radiation for the ionization with UV pulse energies of approximately 30 microjoules in a bandwidth of about 0.4 cm. The focussed UV beam crossed the molecular beam at right angles and could be moved over a variety of radii and angles about the scattering sample surface. Ionized NO molecules were detected using a Johnston MM-1 multiplier. 

Fig.4.69a-e. Output signals at the poly-chromator and the three diode arrays of the FPI wavemeter, which had been illuminated by a cw HeNe laser oscillating on two axial modes (a-d). The lowest figure shows the ring intensity pattern of an excimer-pumped single-mode dye laser measured behind a FPI with 3.3 GHz free spectral range [4.70]... 

The short wavelength X = 337 nm of the nitrogen laser permits pumping of dyes with fluorescence spectra from the near UV up to the near infrared. The high pump power available from this laser source allows sufficient inversion, even in dyes with lower quantum efficiency [5.170-5.174]. At present the most important dye laser pumps are the excimer laser [5.175,5.176], the frequency-doubled or -tripled output of high-power Nd YAG or Nd glass lasers [5.177,5.178], or copper-vapor lasers [5.179]. 

The most common pump system for pulsed CARS experiments are two dye lasers pumped by the same pump laser (N2 laser, excimer laser, or frequency-doubled Nd YAG laser). This system is very flexible because both frequencies a) and C02 can be varied over large spectral ranges. Since both the frequency and intensity fluctuations of the dye lasers result in strong intensity fluctuations of the CARS signal, the stability of the dye lasers needs particular attention. With compact and stable systems the signal fluctuations can be reduced below 10% [8.59]. 

K.L. Hohla Excimer-pumped dye lasers - the new generation. Laser Focus 18, 67 (1982)... 

D.J. Brink, D. Proch Efficient tunable ultraviolet source based on stimulated Raman scattering of an excimer-pumped dye laser. Opt. Lett. 7, 494 (1982)... 

Typically, dye lasers are pumped by an intense fixed-frequency laser, the most often used being nitrogen (337 nm), argon ion (488.0, 514.5 nm), XeCl excimer (308 nm). and frequency-doubled and frequency-tripled Nd-YAG (530, 353.3 nm). 

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