Double-beam picosecond laser

Figure 3. A double-beam picosecond laser system that utilizes a silicon-intensified target (SIT) vidicon.

The first photochemical events in vision under physiological conditions have to be studied with picosecond spectroscopy because of the rapid formation 62,63,64>. Earlier observations have been made at low temperature. The formation lifetime of the first intermediate product (prelumirhodopsin) was measured to be less than 6 ps at room temperature 63). A double-beam picosecond spectrometer with a mode-locked Nd YAG laser was used 62). 

Because the picosecond continuum is generated through a highly nonlinear process, its detailed spatial, spectral, and intensity characteristics vary from shot to shot more severely than do the laser pulses used to generate it. In order to achieve a high degree of reliability in our spectral measurements, it is therefore necessary to obtain double beam spectra in which the data are corrected for continuum fluctuations for every shot. 

Using a mode-locked Nd + YAG laser system to generate picosecond sample excitation pulses and picosecond probing continuum pulses in their double beam spectrometer, Spalink et. al. (30) were able to measure difference absorption spectra of irradiated samples of 11-cis-rhodopsin and 9-cis-rhodopsin at selected times after excitation by means of a PAR OMA-2 optical multichannel detection system. The difference absorption spectral data were obtained over the entire spectral range from 410 nm to 650 nm at one time with an OMCD as opposed to the... 

Fig. 4.9 IR spectra of aniline in a supersonic beam from Ref. [41], The upper trace was obtained by IR-UV double-resonance spectroscopy with the use of the nanosecond laser system. The inset shows the expanded spectrum in the CH stretch region. The lower trace is the ionization gain IR spectrum obtained with the picosecond laser system (Reprinted with permission from Ref. [41]. Copyright (2005), American Institute of Physics)...

Nanosecond absorbance transients were measured with a single beam instrument (11). Excitation was provided by a 6-8 ns, 1 mJ 610 nm pulse from a NdrYAG pumped rhodamine dye laser. Absorption transients were either detected with a Hamamatsu R928 (A<900 nm) or R406 (A>900 nm) photomultiplier operating with a 2.5 ns response time. Picosecond absorbance transients were measured with a double beam apparatus (11). 1.5 ps, 1 mJ, 610 nm excitation pulses were generated by using the output of a mode-locked Ar" laser to synchronously pump a rhodamine dye laser. 

The two-photon absorption coefficients, p, for the solutions and films were determined by the intensity-dependent transmission technique that has been described earlier. As before, the laser beam used was obtained from a frequency-doubled Nd YAG laser (of 532 nm wavelength) that was mode locked to produce 30-picosecond pulses. 

An interesting method for generation of a broad wavelength continuum with a time duration of some picoseconds has been deseribed by Busch et al. I61e) By focussing the intense mode locked laser beam from a frequency-doubled neodynium laser into various liquids (H2O, P2O, etc.) a light continuum can be generated which spans several thousand wave numbers and yet has a picosecond pulse duration. This enables absorption spectroscopy measurements to be made in the picosecond time scale. 

This Synchroscan [68] streak camera system has been used to study the time resolved fluorescence of trans-stilbene in the picosecond time regime. The experimental arrangement [69] is shown in Fig. 20. An acousto-optically mode-locked argon ion laser (Spectra Physics 164), modulated at 69.55 MHz was used to pump a dye laser. The fundamental of this dye laser, formed by mirrors M, M2, M3 and M4, was tunable from 565 to 630 nm using Rhodamine 6G and second harmonic output was available by doubling in an ADP crystal placed intracavity at the focal point of mirrors M5 and M6. The peak output power of this laser in the ultraviolet was 0.35W for a 2ps pulse which, when focused into the quartz sample cell of lens L, produced a typical power density of 10 KW cm-2. Fluorescence was collected at 90° to the incident beam and focused onto the streak camera photocathode with lens L3. The fluorescence was also passed through a polarizer and a bandpass filter whose maximum transmission corresponded to the peak of the trans-stilbene fluorescence. 

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... 

Fig. S.7 SFG spectrometer at the University of Houston. A picosecond-pulsed Nd YAG laser (Eskpla) at 1054 nm is split into two parts. One part is frequency doubled to 532 nm. The other part is used to pump a KTP/AgGaSe2 OPG/OPA system (LaserVision) that generates infrared light (IR). Both beams are directed to the liquid sample. (1) Attenuator (half-wave plates/ polarizer). (2) A/2 plate (polarization...

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