Laser regenerative amplifier

Very recently, white light continuum pulses of duration ca. 200 fsec, pulse energy ca. 1 / J, and peak wavelength of ca. 780 nm have been generated at repetition rates up to 250 kHz by commercially available Ti sapphire regenerative amplified laser systems. Such systems are very expensive, but the expected easier use, as compared with homemade systems, should open up new research applications for time-resolved fluorescence and absorption techniques in the near-IR. 

A schematic diagram of the non-scanning picosecond fluorescence Kerr gate microscope is depicted in Figure 3.9a. A femtosecond Ti sapphire laser with regenerative amplifier provided femtosecond pulses (800 nm, 1 mJ, 110 fs) at a... 

The femtosecond (fs) laser system consists of a TiiSapphire laser and a regenerative amplifier pumping two independent optical parametric amplifiers that provide laser pulses of around 100 fs duration over a very broad range of wavelengths (250-2000 nm). The signal is detected in the transmitted phase-matching direction lc = k3 + k2 — ki and recorded by a spectrometer with spectral resolution = 2 nm. The spectra are measured by scanning over the... 

The laser system consisted of a home-built Ti sapphire fs laser oscillator and regenerative amplifier (RGA). The pulse duration was 50 fs at 800 nm and 1 kHz repetition rate. The output of the RGA was split into two parts. One part was used as pump pulse. The other part served as a source for the generation of probe pulses with the help of a non-collinear optical parametric amplifier (NOPA, Clark). The sample preparation was explained elsewhere [7]. Briefly, sodium (Alfa Aesar) was used as received and sodium bromide (Alfa Aesar) was dried and re-crystallized under vacuum. The preparation of the samples was carried out in a glovebox under argon atmosphere. Localized electrons were generated by heating the metal-salt mixture to 800 °C, i.e. well above the melting point of the salt. 

Details of the laser systems for pump-probe experiments are described elsewhere [8,10], except for a femtosecond IR probe system. For probing IR wavelengths (5 10 pm), a regenerative amplifier system of a Ti sapphire laser (800 nm wavelength, 160 fs FWHM pulse... 

Immediately upon excitation of an IPCT band with a fs laser at 400 nm, transient absorption was observed for both salts in solutions with a peak at about 600 nm, characteristic of 4,4/-bipyridinium radical cations. Figure 20 shows the transient absorption spectra of PV2+(I )2 in methanol solution. A marked increase in the absorbance of the 4,4/-bipyridinium radical cations took place within 1 ps after excitation. 4,4/-Bipyridinium radical cations were thus formed in a fs time scale by the photoinduced electron transfer from a donor I- to an acceptor 4,4/-bipyridinium upon IPCT excitation [48], The time profiles of transient absorption at 600 nm are shown in Fig. 21 for (a) PV2+(I )2 in a film cast from DME and (b) PV2+(TFPB )2 in DME solutions. Both of them showed a very rapid rise in about 0.3 ps, which was almost the same as the time resolution of our fs Ti sapphire laser measurement system with a regenerative amplifier. Similar extremely rapid formation of 4,4/-bipyridinium radical cations was observed for PV2+(I )2 salts in methanol and dimethylsulfoxide solutions upon IPCT excitation, respectively. These results demonstrated that the charge separated 4,4/-bipyridinium radical cations were formed directly upon IPCT excitation because of the nature of IPCT absorption bands (that the electrons correlated with the IPCT band are transferred partially at the ground state and completely at the excited state). Such a situation is very different from usual photochromism which is caused by various changes of chemical bonds mainly via the excited singlet state. No transient absorption was observed for PV2+(I )2... 

Recent Experimental Approaches Our most recent attempt to investigate the problem of ground-state heterogeneity experimentally uses tunable pump laser pulses derived from a home-made optical parametric amplifier (Fig. 1.9). A white light continuum is used to seed a two-stage optical parametric amplifier pumped by the second harmonic of a regeneratively amplified Ti-sapphire laser... 

Fig. 14.6. Three-dimensional view of the Teramobile. (L) Laser system Ti Sa oscillator and its Nd YAG pump laser LI), stretcher (L2), regenerative amplifier, multipass preamplifier (L3) and their Nd YAG pump laser (LJ,) Multipass main amplifier (L5) pumped by two Nd YAG units (L6) Compressor (L7). (5), Beam expanding system (C), Power supplies D), Lidar detection system [14]...

The time-resolved Raman spectra were measured with a picosecond time-resolved Raman spectrometer which employs a standard pump-probe technique. The details of the spectrometer have been publish elsewhere. The followings are concise description of the apparatus The output from a synchronously pumped mode-locked dye laser is amplified with the output from a cw Nd YAG regenerative amplifier. The second harmonic (294 nm, 2 kHz, 1-2 mW) of the amplified light (588 nm, 3.2 ps, 2 kHz, 15 mW) was used as a... 

Transient spectroscopy experiments were performed with a pump-probe spectrometer [7] based on a home-made original femtosecond Ti saphire pulsed oscillator and a regenerative amplifier system operated at 10 Hz repetition rate. The Tirsaphire master oscillator was synchronously pumped with doubled output of feedback controlled mode-locked picosecond pulsed Nd YAG laser. The pulse width and energy of Ti saphire system after the amplifier were ca. 150 fs and 0.5 mJ, respectively, tunable over the spectral range of 760-820 nm. The fundamental output of the Ti saphire system (790 nm output wavelength was set for present study) splitted into two beams in the ratio 1 4. The more intense beam passed through a controlled delay line and was utilized for sample... 

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