Laser continuous-wave

The efficiency of a helium—neon laser is improved by substituting helium-3 for helium-4, and its maximum gain curve can be shifted by varying the neon isotopic concentrations (4). More than 80 wavelengths have been reported for pulsed lasers and 24 for continuous-wave lasers using argon, krypton, and xenon lasing media (111) (see Lasers). 

A He-Ne continuous wave laser provides an 8-mW source of radiation at 6328 A. Calculate the intensity of the light in photons/sec. The light beam has a 3 mm diameter. How many hours would be required to... 

Such measurement provides the magnitude of birefringence, but not its sign. In addition, identical transmission values will be observed for multiple birefringence orders, that is, whenever the optical path difference, dAn, becomes a multiple of X. The main interest of this method arises from its excellent time resolution, below 1 ms, that is readily achieved using a low-power (e.g., 5 mW) continuous-wave laser and a photodiode. If the sample is initially isotropic, it is possible to follow the birefringence order to obtain quantitative results. For improved accuracy, a second (reference) photodiode or a beam chopper and a lock-in amplifier can be used. 

Hara, A. Takei, M. Takeuchi, F. Suga, K. Yoshino, K. Chida, M. Kakehi, T. Ebiko, Y. Sano, Y. Sasaki, N. 2004. High performance low temperature polycrystalline silicon thin film transistors on non-alkaline glass produced using diode pumped solid state continuous wave laser lateral crystallization. Jpn. J. Appl. Phys., Pt. 1 43 1269-1276. 

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

The large conjugation system required for NIR dyes may render the dyes unstable when continuous excitation is applied. But the best signal-to-noise ratios are obtained when the residence time approaches the average bleaching time of the dye. Therefore, the dye should be able to withstand continuous-wave laser excitations. 

In a typical procedure, a continuous wave laser (50 mW) excites ICG at 780 nm and the fluorescence signal is captured at 830 nm. Subsequent to a bolus injection in the tail vein of the rat, the time-dependent clearance of ICG from plasma can be monitored in real-time as shown in Eig. 9 for three rat data sets. 

A more sophisticated mode of LIE detection is the multiphoton-excitation (MPE) fluorescence [47], which is based on the simultaneous absorption of more than one photon in the same quantum event and uses special lasers, such as femtosecond mode-locked laser [48] or continuous wave laser [49], This mode of LIE detection allows mass detection limits at zeptomole level (1 zepto-mole=10 mol) due to exceptionally low detection background and extremely small detection volume, whereas detection sensitivity in concentration is comparable to that of traditional LIE detection modes. A further drawback is the poor suitability of MPE-fluorescence detection to the on-column detection configuration, which is frequently employed in conventional LIE detection. 

Dr C.K.N. Patel et al of Bell Telephone Laboratories achieved laser action in the IR by passing an electric discharge thru CO2 and CO at very low pressure (about 0.2 torr). Continuous-wave laser action was obtained on a number of rotational transitions of a vibrational band of CO2, the strongest transition occurring at 10.6324 microns. 

J. Manz Prof. V. Engel s question points to the virtues of using (i) ultrashort laser pulses for controlling chemical reactions, in comparison with (ii) continuous-wave lasers. Compare, for example, the strategies of... 

Laser spectroscopy of the 1S-2S transition has been performed by Mills and coworkers at Bell Laboratories (Chu, Mills and Hall, 1984 Fee et al, 1993a, b) following the first excitation of this transition by Chu and Mills (1982). Apart from various technicalities, the main difference between the 1984 and 1993 measurements was that in the latter a pulse created from a tuned 486 nm continuous-wave laser with a Fabry-Perot power build-up cavity, was used to excite the transition by two-photon Doppler-free absorption, followed by photoionization from the 2S level using an intense pulsed YAG laser doubled to 532 nm. Chu, Mills and Hall (1984), however, employed an intense pulsed 486 nm laser to photoionize the positronium directly by three-photon absorption from the ground state in tuning through the resonance. For reasons outlined by Fee et al. (1993b), it was hoped that the use of a continuous-wave laser to excite the transition would lead to a more accurate determination of the frequency interval than the value 1233 607 218.9 10.7 MHz obtained in the pulsed 486 nm laser experiment (after correction by Danzmann, Fee and Chu, 1989, and adjustment consequent on a recalibration of the Te2 reference line by McIntyre and Hansch, 1986). 

Output from both gated continuous wave and pulsed carbon dioxide lasers has been used to desorb ions from surfaces and then to photodissociate them in a Fourier transform ion cyclotron resonance mass spectrometer. Pulsed C02 laser irradiation was most successful in laser desorption experiments, while a gated continuous wave laser was used for a majority of the successful infrared multiphoton dissociation studies. Fragmentation of ions with m/z values in the range of 400-1500 daltons was induced by infrared multiphoton dissociation. Such photodissociation was successfully coupled with laser desorption for several different classes of compounds. Either two sequential pulses from a pulsed carbon dioxide laser (one for desorption and one for dissociation), or one desorption pulse followed by gated continuous wave irradiation to bring about dissociation was used. 

The availability of laser scanning confocal fluorescence microscopy,68 first commercially offered in the 1980s, enabled a major advance in chemical microscopy imaging convenient summaries are available in the Handbook of Biological Confocal Microscopy.69 Confocal fluorescence microscopy works by focusing continuous-wave laser illumination to a diffraction-limited spot in a focal... 

CARS CAT CCD CIF CPMD CT CTAB CW Coherent Anti-Stokes Raman Scattering Computerized Axial Tomography Charge-Coupled Device Chemical Image Fusion Carr-Parrinello Molecular Dynamics Computed Tomography Cetyltrimethylammonium Bromide Continuous Wave (Laser)... 

Working in the frequency domain, the sample is excited by light whose intensity is sinusoidally modulated at high frequency (typically MHz). Light from a continuous wave laser (e.g., the 488 nm line from... 

Continuous-wave laser technology directs a continuous laser beam at the target, and the distance is calculated on the basis of frequency, wavelength, and phase shift in the returning beam. It is used for short-range, extremely high-accuracy, clean-air applications usually for positioning and only infrequently for level. 

A typical experimental ellipsometer is illustrated in Figure 3.7. Monochromatic light, typically from a continuous wave laser, e.g. a He-Ne laser, is plane polarized (the angle of polarization is given by p) and impinges on a surface. A compensator is then used to convert the elliptically polarized reflected beam to a plane polarized beam (with a being the angle of polarization). The analyzer then determines the... 

Observations of Fast Turbulent Mixing in Gases Using a Continuous-Wave Laser... 

It ought to be pointed out that the methods of transfer of population and also of polarization between the states are being developed further. One might mention, in particular, the cw all-optical triple resonance (AOTR) method evolved by Stwalley s group [282] and tried out on Na2-The method consists of the use of three tunable single-frequency continuous wave lasers allowing flexible movement of both population and polarization from the thermally populated level to any other level of the ground state. 

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