Laser synchronously pumped

The commercially available laser source is a mode-locked argon-ion laser synchronously pumping a cavity-dumped dye laser. This laser system produces tunable light pulses, each pulse with a time duration of about 10 picoseconds, and with pulse repetition rates up to 80 million laser pulses/second. The laser pulses are used to excite the sample under study and the resulting sample fluorescence is spectrally dispersed through a monochromator and detected by a fast photomultiplier tube (or in some cases a streak camera (h.)) ... 

The single photon counting apparatus will be described elsewhere. For these experiments, we utilized the laser dye Styryl 9 in a cavity-dumped dye laser synchronously-pumped by a mode-lock Nd YAG laser. Using this instrument we were able to excite the sample between 800 and 890 nm at a repetition rate of 3.8 MHz. 

Picosecond transient absorption was monitored on a spectrometer consisting of two dye lasers synchronously pumped by an actively mode-locked, actively Q-switched Nd-YAG laser (JK-AML 2000). Single pulses... 

Several laser systems have been used in our time-resolved PM measurements. For the ultrafast measurements, a colliding pulse mode-locked (CPM) dye laser was employed [11]. Its characteristic pulsewidth is about 70 fs, however, its wavelength is fixed at 625 nin (or 2.0 cV). For ps measurements at various wavelengths two synchronously pumped dye lasers were used (12], Although their time resolution was not belter than 5 ps, they allowed us to probe in the probe photon energy range from 1.25 cV to 2.2 cV. In addition, a color center laser... 

Fig. 6.12. Data obtained by the single-photon wavelength 340 nm observation wavelength timing technique using a mode-locked ion- 390 nm. Reference scattering solution argon laser that synchronously pumps a cavity- (Ludox). Number of channels 900 channel dumped dye laser. Sample solution of POPOP width 4.68 ps. Result t = 1.05 + 0.01 ns in cyclohexane (undegassed). Excitation x = 1.055.

More recently Ghiggino and co-workers(32) have applied laser scanning confocal fluorescence lifetime microscopy to the study of polyvinyl alcohol films containing rhodamine B (650 nm emission) and cresyl violet (632 nm emission). Synchronously pumped dye laser excitation and APD detection were used with optical fiber coupling. A schematic diagram of their apparatus is shown in Figure 12.5. 

Laser II A femtosecond mode-locked dye laser (Coherent, Satori) synchronously pumped using a cw mode-locked and frequency-doubled Nd YAB laser (Coherent, Antares), generating pulses in 76 MHz repetition rate and 250-fs fwhm. 

Laser III A picosecond mode-locked and cavity-dumped dye laser (Spectra-Physics, 375B and 344S) synchronously pumped using a cw mode-locked argon ion laser (Spectra-Physics, 2030-18), generating tunable (530-830 nm) pulses in 4-MHz repetition rate and 10-ps fwhm. 

These features are exploited in an experiment which is taking place in our laboratory. A schematic diagram of this experiment is shown in figure 4. The system consists of an all-lines violet mode-locked Kr+ ion laser operating at a repetition rate of about 250 MHz Which synchronously pumps a C102 dye laser. The dye laser typically produces about 300 mW of average power and pulse durations of about 3 psec. This is frequency doubled to 243 nm in a crystal of p-barium borate to produce in excess of 2 mW average power. The output from the second harmonic crystal is then mode-matched into an ultra-violet enhancement cavity. The free... 

Figure 6-5 RR spectra obtained with 576 nm pulsed laser excitation from a synchronously pumped dye laser, (a) and (b), the Hb—Co photoproduct obtained with 30ps and 20ns pulses, respectively, (c) Deoxy-Hb. (Reproduced with permission from Ref. 8.)...

Picosecond pulses can be produced in a number of different types of laser systems. As an example, a brief description is first given of a synchronously pumped c.w. dye laser such as can be readily assembled from commercially available units. Generation of repetitive subnanosecond pulses in a c.w. laser by mode-locked synchronous pumping was first described by Harris et al. [12]. The essential features of such a system are shown in Fig. 3. In this system, an acousto-optically mode-locked ion laser is used to pump the dye laser. In order to achieve synchronous pumping, the length of the dye cavity must be adjusted so that the dye laser intermode spacing is an integral multiple of the pump mode-locker frequency. 

Fig. 3. Diagram of a synchronously pumped picosecond-pulse dye laser.

The output is thus a continuous train of pulses separated by the dye cavity round-trip time. Even though the pump laser pulses may be of the order of 200 ps long, dye laser pulses of less than 10 ps can be achieved by synchronous pumping. This is because the dye molecules have extremely large stimulated emission cross-sections and the dye laser pulse passing through the dye stream immediately de-excites the dye molecule, in a few picoseconds, by stimulated emission [13]. 

Time correlated single photon counting is a well-established technique that has been used to measure fluorescence lifetimes since the mid-1960 s. These early experiments, which used a variety of flashlamps and gaseous gap-discharge arcs as the excitation source, were reviewed by Ware [47, 48] in 1971. The traditional light sources have been replaced by laser sources in recent experiments, thus markedly extending the range of applications of this technique. Particularly well suited excitation sources for this method are the mode-locked lasers and synchronously pumped dye lasers which are capable of operation at MHz repetition rates. 

C.K. Chan, Synchronously Pumped Dye Lasers, Spectra Physics Laser Technical Bulletin, No. 8, 1978. 

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