Light sources pulsed lasers

Fig. 7.3 Experimental setup for the nanosecond laser Flash Photolysis with a white light continuum. A Brilland-Quantel Nd YAG laser delivers the fundamental pulses (355 and 532 nm). A pulsed XBO lamp is used as white light source. The laser signal is split in order to trigger the digital storage oscilloscope (DSO) utilizing a second photodiode (PD). Two separate detection units in different geometries—photomultiplier (PMT) in front face and a PD in side face—detect the signal in the UV/vis and NIR region, respectively. The monochromator is operated by a standard PC...

Figure 1 shows the schematic diagram of the experimental apparatus. The transversely excited atmospheric pressure CO2 pulse laser (LUMONICS TEA-841) was used as a light source. The laser beam was slightly converged by a ZnSe lens with a focal length of 1.5 m and introduced into a reaction cell. The reaction cell was a cylindrical stainless steel tube, 2000 mm long x 54.6 mm inner diameter, equipped with NaCl windows at both ends. The wavenumber of the laser was set... 

Fluorescence can be resolved overtime. The use of very short pulsed light sources (picosecond lasers and laser diodes) has rendered accessible graphs of fluorescence decay as a function of the time. New applications based upon a greater knowledge of the lifetime are under development, although they are still not used much in chemical analysis. 

The fluorescence lifetime measurements were performed with a streak camera (Agat SF 3M, VNIIOFI, Russia). A Nd YAG laser with excitation wavelengths of 532 and 266 nm (the second and fourth harmonic of fundamental radiation) was used as a light source. The laser radiation parameters of the fluorimeter were as follows (for 532 nm) pulse energy 160 (ij, duration 20 ps (fwhm), beam diameter 5 mm. The error in determining the fluorescence lifetimes in time intervals of several nanoseconds did not exceed 5 %. In addition to the laser equipment, the Cary 100 spectrophotometer (Varian, Inc., USA) and the Cary Eclipse spectrofluorimeter (Varian, Inc., USA slits width was 5 nm) were used for optical density measurements and fluorescence registration, respectively. 

Another key consideration in the design of trapping MS combined with optical spectroscopy experiments is the choice of light source. Here, we limit the discussion to that convenient modem light-source, the laser, which emits typically light that is highly directional and monochromatic (except for ultrashort pulses that can exhibit spectral widths of several dozens of nanometers). Laser selection criteria include... 

GVD effect can be cancelled out, and the original pulse width can be recovered at the aperture of the near-field probe. In this way, high time resolution can be achieved while retaining the high spatial resolution of a near-field optical microscope. For time-resolved and non-linear near-field measurements, a mode-locked HiSapphire oscillator (TSL) is useful as a light source. Amplified lasers, which are frequently used for far-field time-resolved measurements, are not compatible with the aperture near-field probe because pulses with high power break the near-field tip easily by thermal effects. Moderate peak power is desirable for combination with aperture near-field probes. 

The foremost of the modem teclmiques is tlie use of lasers as spectroscopic tools. Lasers are extremely versatile light sources. They can be designed with many usetlil properties (not all in the same instmment) such as high intensity, narrow frequency bandwidth with high-frequency stability, tunability over reasonable frequency ranges, low-divergence beams which can be focused into very small spots, or pulsed beams with... 

Figure B2.1.1 Femtosecond light source based on an amplified titanium-sapphire laser and an optical parametric amplifier. Symbols used P, Brewster dispersing prism X, titanium-sapphire crystal OC, output coupler B, acousto-optic pulse selector (Bragg cell) FR, Faraday rotator and polarizer assembly DG, diffraction grating BBO, p-barium borate nonlinear crystal.

One of the most important teclmiques for the study of gas-phase reactions is flash photolysis [8, ]. A reaction is initiated by absorption of an intense light pulse, originally generated from flash lamps (duration a=lp.s). Nowadays these have frequently been replaced by pulsed laser sources, with the shortest pulses of the order of a few femtoseconds [22, 64]. 

As it stands, the picture of dynamics from Eq. (29) is derived from the interaction of molecules with a continuous light source, that is, the system is at equilibrium with the oscillating light field. It is also valid if the light source is an infinitely short laser pulse, as here all frequencies are instantaneously excited. 

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. 

A source of light for excitation. Surfece studies generally require a continuous or pulsed laser. A dye or Tlisapphire laser is used if tunability is needed. 

A Q-switched Nd YAG laser (7 ns pulse duration, Quanta-Ray DRC-1A) operated at 10 Hz was used as a light source. The 1064 nm fundamental was frequency doubled to 532 nm for some experiments. In all experiments reported here a geometry was used which focused the laser beam in front of the entrance window of the sample cell such that the laser beam was diverging as it passed through the sample cell. In this geometry the laser beam was about 3 mm in diameter at the region viewed by the light detection system. 

Chan HH, Kono T (2004) The use of lasers and intense pulsed light sources for the treatment of pigmentary lesions. Skin Therapy Lett 9(8) 5-7... 

In addition, combining the microscope with the use of a pulsed laser light source provides temporal information on these systems in a small domain. The dispersion of refractive index, however, strongly affects the temporal resolution in the measurements of dynamics under the microscope and typical resolution stays around 100 fs when a Ti Sapphire laser is used as an excitation source. 

With the aim of elucidating molecular dynamics in a small domain, we have constmcted several microspectroscopic systems, that is, (i) the confocal microscope with the excitation light source being a femtosecond NIR laser emitting a 35 fs pulse, and (ii) the fluorescence correlation spectroscopic system with optical tweezers. 

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