Pumping laser

For some experiments, it may be helpfiil to obtain a reference signal to correct for fluctuations and long-tenu drift in the pump laser. This correction is best accomplished by perfonumg simultaneous measurements of the... 

In a typical time-resolved SHG (SFG) experiment using femtosecond to picosecond laser systems, two (tlnee) input laser beams are necessary. The pulse from one of the lasers, usually called the pump laser, induces the... 

A wide variety of metliods has been used to pump laser systems. Altliough optical pumping has been implied, tliere is an array of collisionally or electron impact pumped systems, as well as electrically pumped metliods. The efficiency of tire pumping cycle in many ways defines tire utility and applications of each scheme. The first... 

The light source for excitation of Nd YAG lasers may be a pulsed flashlamp for pulsed operation, a continuous-arc lamp for continuous operation, or a semiconductor laser diode, for either pulsed or continuous operation. The use of semiconductor laser diodes as the pump source for sohd-state lasers became common in the early 1990s. A variety of commercial diode-pumped lasers are available. One possible configuration is shown in Figure 8. The output of the diode is adjusted by composition and temperature to be near 810 nm, ie, near the peak of the neodymium absorption. The diode lasers are themselves relatively efficient and the output is absorbed better by the Nd YAG than the light from flashlamps or arc lamps. Thus diode-pumped sohd-state lasers have much higher efficiency than conventionally pumped devices. Correspondingly, there is less heat to remove. Thus diode-pumped sohd-state lasers represent a laser class that is much more compact and efficient than eadier devices. 

FPY (fluor. photons emitted)/(pump laser photons absorbed) (1)... 

This estimated FPY was based on the reported molar absorptivity of PuF6 at the pump laser wavelength, the pressure of PuF6 in... 

Pump laser photon absorption, fluorescence photon yield. 163-64... 

Farrow R. L., Rahn L. A. Interpreting coherent anti-Stokes Raman spectra measured with multimode Nd YAG pump lasers, J. Opt. Soc. Am. B2, 903-7 (1985). 

The overall conceptual layout of the pulsed dye laser LGS system is shown in Fig. 18. A thermally insulated room located on the dome floor houses much of the laser system to minimize vibrations on the telescope and the heat dissipated within the dome. The enclosure houses 6 frequency-doubled Nd YAG pump lasers, the DM0, the associated laser electronics and diagnostics, the... 

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

The pump lasers were designed and built at LLNL. Two laser cavity configurations are employed. Two "L" shaped cavities run at the full system repetition rate of 26 kHz, producing 40-50 W per laser. They pump the DM0 and preamplifier dye cells. Four "Z" cavity lasers run at 13 kHz, each producing between 60-80 W. They are interleaved in the power amplifier dye cell to produce an effective 26 kHz repetition rate. Flashlamps were used to pump the frequency-doubled YAG lasers as diode-pumps were much more expensive at the time the Keck LGS was designed. In addition, high wavefront quality is not required... 

We have shown the different aspects of Optical Parametric Oscillators which explain the present interest for these sources, in fundamental as well as in applied physics. The very rapid development of compact, not power demanding sources including the pump laser and the OPO, should lead to an even wider use of such sources, in particular for industrial or medical applications. 

Figure 1.3. Real-time femtosecond spectroscopy of molecules can be described in terms of optical transitions excited by ultrafast laser pulses between potential energy curves which indicate how different energy states of a molecule vary with interatomic distances. The example shown here is for the dissociation of iodine bromide (IBr). An initial pump laser excites a vertical transition from the potential curve of the lowest (ground) electronic state Vg to an excited state Vj. The fragmentation of IBr to form I + Br is described by quantum theory in terms of a wavepacket which either oscillates between the extremes of or crosses over onto the steeply repulsive potential V[ leading to dissociation, as indicated by the two arrows. These motions are monitored in the time domain by simultaneous absorption of two probe-pulse photons which, in this case, ionise the dissociating molecule.

Figure 1.4. Experimental and theoretical femtosecond spectroscopy of IBr dissociation. Experimental ionisation signals as a function of pump-probe time delay for different pump wavelengths given in (a) and (b) show how the time required for decay of the initally excited molecule varies dramatically according to the initial vibrational energy that is deposited in the molecule by the pump laser. The calculated ionisation trace shown in (c) mimics the experimental result shown in (b).

A qualitatively different approach to probing multiple pathways is to interrogate the reaction intermediates directly, while they are following different pathways on the PES, using femtosecond time-resolved pump-probe spectroscopy [19]. In this case, the pump laser initiates the reaction, while the probe laser measures absorption, excites fluorescence, induces ionization, or creates some other observable that selectively probes each reaction pathway. For example, the ion states produced upon photoionization of a neutral species depend on the Franck-Condon overlap between the nuclear configuration of the neutral and the various ion states available. Photoelectron spectroscopy is a sensitive probe of the structural differences between neutrals and cations. If the structure and energetics of the ion states are well determined and sufficiently diverse in... 

A computer-controlled motorized translation stage mounted with a retro-reflector is used to vary the pump laser beam path relative to the probe laser beam path and this controls the relative timing between the pump and probe laser beams. Note that a one-foot difference in path length is about 1 ns time delay difference. The picosecond TR experiments are done essentially the same way as the nanosecond TR experiments except that the time-delay between the pump and probe beams are controlled by varying their relative path lengths by the computer-controlled motorized translation stage. Thus, one can refer to the last part of the description of the nanosecond TR experiments in the preceding section and use the pump and probe picosecond laser beams in place of the nanosecond laser beams to describe the picosecond TR experiments. 

Photolysis of the 2-fluorenyl azide precursor compound by the 267 nm pump laser pulse releases a nitrogen molecule and produces the singlet 2-fluorenylnitrene intermediate as shown in Scheme 3.2. In the presence of appreciable amounts of water, this singlet 2-fluorenylnitrene species can react with the water molecule to form a singlet 2-fluorenylnitrenium ion and an OH species as shown in Scheme 3.2. 

Fig. 5. Effect of the dissociation rate on the ion image intensity distribution, (a) Simulated translational energy distribution, (b), (c) Image intensity distributions that would result from (a) if the dissociation lifetime was 0.1/rs and 15/l

The results for the A state show that a different mechanism is operative. A series of femtosecond pump-probe experiments were performed at wavelengths corresponding to the Rydberg states A (v = 0,1,2) of ammonia molecules.64-66,68,69 The wavelengths used to access these vibrational levels were 214 nm, 211 nm, and 208 nm for the pump laser and 321 nm, 316.5 nm, and 312 nm for the probe laser, respectively. 

From the discussion presented in previous sections, vibrational relaxation (Appendix II) plays a very important role in the initial ET in photosynthetic RCs. This problem was first studied by Martin and co-workers [4] using Rb. capsulatas Dll. In this mutant, the ultrafast initial ET is suppressed and the ultrafast process taking place in the ps range is mainly due to vibrational relaxation. They have used the pumping laser at Xpump = 870 nm and probed at A.probe = 812 nm at 10 K. The laser pulse duration in this case is 80 fs. Their experimental results are shown in Fig. 16, where one can observe that the fs time-resolved spectra exhibit an oscillatory build-up. To analyze these results, we use the relation... 

We consider a model for the pump-probe stimulated emission measurement in which a pumping laser pulse excites molecules in a ground vibronic manifold g to an excited vibronic manifold 11 and a probing pulse applied to the system after the excitation. The probing laser induces stimulated emission in which transitions from the manifold 11 to the ground-state manifold m take place. We assume that there is no overlap between the two optical processes and that they are separated by a time interval x. On the basis of the perturbative density operator method, we can derive an expression for the time-resolved profiles, which are associated with the imaginary part of the transient linear susceptibility, that is,... 

The system used to measure the optical fiber signals employs two separate frequency tunable laser light sources operating at about 1320 nm wavelength. One laser acts as a pump laser, whereas the other serves as the probe laser that sends optical pulses down the fiber to interact with the counterpropagating laser light wave pumped into the fiber from its opposite end. 

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