Laser attenuator

The narrowest PFI bands in the present study are 3 cm-1 FWHM, using a 0.5 V/cm extraction field with the lasers attenuated to minimize effects of space charge. We measure band positions at the intensity maxima. These are reproducible to better than 1 cm-1. The bandwidth is limited by the rotational contour and also by the ionization process. A major advantage of ZEKE-PFI over more traditional photoelectron techniques is that the energy calibration is that of the tunable dye lasers, which are quite stable from day to day. In contrast, both electrostatic analyzers and time-of-flight photoelectron spectrometers require frequent calibration. 

Gavish L, Perez LS, Reissman P, Gertz SD (2008) Irradiation with 780 nm diode laser attenuates inflammatory cytokines but upregulates nitric oxide in lipopolysaccharide-stimulated macrophages implications for the prevention of aneurysm progression. Lasers Surg Med 40(5) 371-378... 

The light source used in the light scattering experiment was He-Ne laser, attenuated to produce a power of lOmW, and the wavelength was 0.6328 pm. The thickness of the specimen for the light scattering experiment was 20 pm. 

MALDI TOP (7) mass spectra were recorded on a Bruker Reflex instrument (Billerica, MA). The rp-HPLC fractions containing PMP labeled oligosaccharides were dried in a SpeedVac concentrator (Farmingdale, NY) and redissolved in water/acetonitrile (75/25, v/v). 2,5-Dihydroxybenzoic acid (DHB) was used as a matrix. Normally, 0.3 uL of a half-saturated solution of DHB in water/acetonitrile/trifluoroacetic acid (70/30/0.1, v/v) was mixed on the sample dish with 0.3 pL of the sample solution. Desorption and ionization was done with a nitrogen laser (337 nm) adjusted to minimum laser attenuation. Mass spectra (10 to 20) were accumulated in linear negative ionization mode with an acceleration voltage of 25 kV. Calibration was done externally with bovine insulin and angiotensin I. 

The manufacturer s software automatically adjusts the Laser attenuation and measnrement position. For each size and zeta potential determination, 3 measurements consisting of 6 sub runs with a duration of 10 s are averaged. 

Alternatively, size selection can be performed after the event of e.g. predissociation. In this case the laser attenuation of a size-selected beam signal of "cold" complexes is measured. Both methods have been used successfully, as described in the contribution of U. Buck to this volume. 

For dielectric rejection filters, the low Raman shift cutoff lies somewhere between 200 and 600 cm making observation of many inorganic materials difficult. Lewis et al. [79] were able to extend the low-wave-number range of these filter by demonstrating that by angle tuning the filters, the lower-wave-number cutoff can be shifted to a lower wave number, albeit at the expense of laser attenuation ability. 

The general setup of LDI/MALDI ion sources is comparatively simple (Fig. 11.2) [25]. Both LDI and MALDI make use of the absorption of laser light by a solid sample layer. The energy uptake upon laser irradiation then causes evaporation and eventually ionization of the sample. The pulse of laser hght is focused onto a small spot which is typically 0.05-0.2 mm in diameter [26]. As laser irradiance is a critical parameter in MALDI, a variable beam attenuator in the laser optical path is employed to adjust the irradiance, e.g., by means of a rotatable absorbing filter of variable transmittance from close to 100% down to about 1%. Then, the laser attenuation is individually optimized for each measurement. LDI/MALDI ion sources are generally operated at ambient tenperature. 

Safety Standards. Protection from laser beams involves not allowing laser radiation at a level higher than a maximum permissible exposure level to strike the human body. Maximum permissible exposure levels for both eyes and skin have been defined (55—57). One of the most common safety measures is the use of protective eyewear. Manufacturers of laser safety eyewear commonly specify the attenuation at various laser wavelengths. Under some conditions safety eyewear has been known to shatter or to be burned through (58), and it is not adequate to protect a wearer staring directly into the beam. 

Laser communication systems based on free-space propagation through the atmosphere suffer drawbacks because of factors like atmospheric turbulence and attenuation by rain, snow, haze, or fog. Nevertheless, free-space laser communication systems were developed for many appHcations (89—91). They employ separate components, such as lasers, modulators, collimators, and detectors. Some of the most promising appHcations are for space communications, because the problems of turbulence and opacity in the atmosphere are absent. 

The well-defined large bimetallic Au—Ag cluster as [(Ph3P)i2AuigAg2oCli4] can achieve nearly two orders of magnitude of attenuation of high-intensity laser power and, consequently opens the door to a new class of optical materials based on nanosized metal clusters 3269... 

For comparison purposes, two other MS systems have been used with in vitro grown parasite cultures. In the first case, a home-built miniaturized linear TOF multi-array analyzer1718 was interfaced to the frequency-tripled output at 355nm of a Q-switched Nd-YAG laser ( Polaris, New Wave Research, Fremont, CA). In this experiment the laser beam was not scanned, and the estimated laser fluence after attenuation was similar to that of the commer-... 

Fig. 6. Schematic diagram of the Nottingham apparatus for IR kinetic measurements on solutions. Solid lines represent the light path, broken lines the electrical connections. L = Line tunable CO laser, S = sample cell, F = flash lamp, P = photodiode, D = fast MCT IR detector, T = transient digitizer, O = oscilloscope, and M = microcomputer. Nonfocussing optics were used throughout, and the IR laser beam was heavily attenuated by a variable path cell V, filled with liquid methanol, placed immediately in front of the detector. [Reproduced with permission from Moore et al. (61).]...

Photoionization ti me-of-fli ght mass spectrometry is almost exclusively the method used in chemical reaction studies. The mass spectrometers, detectors and electronics are almost identical. A major distinction is the choice of ionizing frequency and intensity. For many stable molecules multi photon ionization allowed for almost unit detection efficiency with controllable fragmentation(20). For cluster systems this has been more difficult because high laser intensities generally cause extensive dissociation of neutrals and ions(21). This has forced the use of single photon ionization. This works very well for low i oni zati on potential metals ( < 7.87 eV) if the intensity is kept fairly low. In fact for most systems the ionizing laser must be attenuated. A few very small... 

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