Lasers coherence

With development of ultrashort pulsed lasers, coherently generated lattice dynamics was found, first as the periodic modulation in the transient grating signal from perylene in 1985 by De Silvestri and coworkers [1], Shortly later, similar modulation was observed in the reflectivity of Bi and Sb [2] and of GaAs [3], as well as in the transmissivity of YBCO [4] by different groups. Since then, the coherent optical phonon spectroscopy has been a simple and powerful tool to probe femtosecond lattice dynamics in a wide range of solid... 

Figure 2.23 shows the broad spectral region covered by an OPO system, using as a pump wavelength the Q-switched radiation at 355 nm from a system based on a Nd YAG laser. Coherent radiation that is tunable from 400 nm to 2 jam can be obtained from the signal and idler waves. 

Femtosecond Ti-Sapphire oscillator (CDP, TiF50, 100 fs, 80 MHz, 0.3 W, 800 run) pumped with diode pumped solid state laser (Coherent, Verdi) was used to excite the system. The time- and spectral-resolved fluorescence spectra of C522 were measured by using up-conversion set-up (CDP, FOG100). The p-cyclodextrin, C42H70O35, and coumarin C522, C14H12F3NO2, used in these experiments were produced by Cyclolab and Radiant Dyes Chemie, respectively. All experiments were performed at room temperature and used water was twice deionised. 

The fact that this control scenario does not require laser coherence makes it especially attractive for laboratory use since generally available, non-transform limited, nsec dye lasers can be used. In our experiment we use two dye lasers pumped by a frequency-doubled Nd-Yag laser. One dye laser, whose frequency a>2 was tuned between 13,312 cm- and 13,328 cm-1, was used... 

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 IV A diode-laser-pumped and frequency-doubled (532 nm) cw Nd YAG laser (Coherent, DPSS 532). 

Numerical studies [193] show that Eq. (5.54) provides a zeroth-order approxima-" tfon to the results of a full computation, which underestimates the degree of possible control in a realistic system. In addition, these results show that even for phase f tpfusion fields, which have widths on the order of wavenumbers, control is still - msive (e.g., Co 5). Examination of the experimental results on one-photon vs. 1-e-photon control show, however, contrast ratios on the order of 30% [76, 194], Tjhat is, the main experimental limitation, thus far, is due to experimental issues other (rihe partial laser coherence. 

The numerical solutions to the original equations [Eqs. (11.30) and (11.31)] ai g plotted in Figures 11.4 and 11.5 and contrasted with the experimental results off [201], These experiments are made easier by the fact that the 11C control sc does not require laser coherence, hence, generally available, nontransform-li... 

Table 7.1. Comparison of main parameters of an excimer laser Coherent Lambda Physik LPX305iF [32], and of a pulsed solid state Nd YAG laser Quantel YG981E [33], both suitable for research PLD systems...

The frequency chain works as follows to the second harmonic of the He-Ne laser at 3.39 jum a NaCl OH color center laser at 1.70 pm is phase locked. To the second harmonic of the color center laser a laser diode at 848 nm is then phase locked. This is accomplished by first locking the laser diode to a selected mode of the frequency comb of a Kerr-lens mode-locked Ti sapphire femtosecond laser (Coherent model Mira 900), frequency-broadened in a standard single-mode silica fiber (Newport FS-F), and then controlling the position of the comb in frequency space [21,11]. At the same time the combs mode separation of 76 MHz is controlled by a local cesium atomic clock [22]. With one mode locked to the 4th harmonic of the CH4 standard and at the same time the pulse repetition rate (i.e. the mode separation) fixed [22], the femtosecond frequency comb provides a dense grid of reference frequencies known with the same fractional precision as the He-Ne S tandard [23,21,11]. With this tool a frequency interval of about 37 THz is bridged to lock a laser diode at 946 nm to the frequency comb, positioned n = 482 285 modes to lower frequencies from the initial mode at 848 nm. 

We have developed FM lasers based on a commercial ring laser (Coherent 699-21). In this case all the intracavity etalons are removed and replaced by a lithium niobate phase modulator. This modulator can be resonantly driven at a frequency close to the cavity mode spacing. A simple theory of FM operation of a laser suggests that the modulation index is given by [12]... 

Jobin-Yvon Ramanor HG-2S spectrometer with double monochromator. Red light of 647 nm from a krypton-ion laser (Spectra Physics Model 165) and 514.5. 488 and 457.9 nm radiation from an argon-ion laser (Coherent Radiation Co., Model CR-2) were used. 

The arrangement employed for the VPC experiment is described in Reference 4. A cw argon-ion laser at 488 nm was used in a standard DFWM geometry. The s-polarized output beam was first split by a beam-splitter to provide the pump and the probe beams. The transmitted beam from the beam-splitter was then divided into the two s-polarized pump beams each with a power of approximately 0.35 mW. The reflected beam from the beamsplitter was used as the probe beam, whose intensity was about 7% of the total intensity in both pump beams. The forward pump beam and the probe, which constituted writing beams, were overlapped at the sample. Their optical path length difference was much smaller than the laser coherence length, so that they were coherent at the sample. The backward pump beam was... 

An ultraviolet fluorescence excitation beam was generated with an intracavity frequency doubled argon ion laser (Coherent, FRED) providing a tunable wavelength range of 229 - 264 nm. The excitation beam was focused onto the sample with a 10 cm lens to give a spot size of 60-70 pm. For fluorescence experiments, front-face illumination geometry was used. The... 

A variety of laser sources have been applied to photodynamic therapy trials. These have included dye lasers (Coherent Lambda Plus, Santa Clara, CA or Laserscope Model 630, San Jose, CA) which use one source of laser energy (argon or KTP-YAG) to drive a dye (kiton red) to produce a red light. These laser systems usually require special power outlets and water cooling to function properly. Recently, a solid state diode laser has been produced (Diomed 630 PDT, Cambridge, UK) which can be operated from standard power outlets and can be air-cooled. This diode laser can supply up to 2 W of power at 630 nm, which is sufficient to activate porphyrin compounds. 

Z. Chen, M. Shapiro, P. Brumer, Interference control without laser coherence Molecular photodissociation, J. Chem. Phys. 102 (1995) 5683... 

Single crystals of (BEDT-TTF)2Cu(NCS)2 have been obtained by electrochemical preparation The largest crystals obtained in this way (10x2x0.1 mm have been selected and oriented in a patchwork of about 10 mm. The Raman spectra have been carried out with the lines of an Ar ion laser (Coherent Innova 90) in a 90° scattering configuration. The laser beam was filtered with a monochromator and a proper interference filter in order to prevent plasma lines. 

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