Helium-neon laser sources

Lasers (see Chapter 9) are sources of intense, monochromatic radiation which are ideal for Raman spectroscopy and have entirely replaced atomic emission sources. They are more convenient to use, have higher intensity and are more highly monochromatic for example, the line width at half-intensity of 632.8 nm (red) radiation from a helium-neon laser can be less than 0.05 cm. ... 

How can phase-modulation fluorometry contribute to this health-care need It now seems possible to construct a lifetime-based blood gas catheter (Figure 1.3), or alternatively, an apparatus to read the blood gas in the freshly drawn blood at the patient s bedside. To be specific, fluorophores are presently known to accomplish the task using a 543-nm Green Helium-Neon laser,(18 19) and it seems likely that the chemistries will be identified for a laser diode source. The use of longer wavelengths should minimize the problems of light absorption and autofluorescence of the samples, and the use of phase or modulation sensing should provide the robustness needed in a clinical environment. For the more technically oriented researcher, we note that the... 

Low Angle Laser Light Scattering Photometry. Weight-average molecular weights were determined with a KMX-6 photometer (LDC/Milton Roy). The light source was a 2 mW vertically polarized helium-neon laser (A =... 

These measurements were made on an Auto EL-II Ellipsometer (Rudolph Research, Flanders, NJ). The laser source was a 1 mW continuous wave helium/ neon laser, with a wavelength of 6328 A. The angle of incidence was 70° and the spot size 2-3 mm. A refractive index of 1.5 was utilized for all the silane layers. The data were analysed on a Hewlett-Packard 85 computer using film 85 software package, version 30, program 13, and the film thickness was calculated using the McCrackin program. 

The sample is introduced into the separation channel by electromigration injection. Thus far, detection has been solely by laser-induced fluorescence, using an argon ion laser or a helium/neon laser as the excitation source and a photomultiplier tube (PMT) or charge-coupled device (CCD)... 

The assay itself is performed in a 96 well plate. DMSO stock solution is diluted 20 fold in PBS (0.01 M, pH 7.4). The diluted solution is again diluted 10 times with 5% DMSO/95% PBS across the 96 well plate in order to keep 5 % DMSO content stable. The solubility assay is performed with 2 replicates for each compound, thus 8 compounds can be measured per well. Detection of the precipitation is done with a helium/neon laser nephelometer (BMG Labtech-nologies, Offenburg, Germany). The instrument lases at 632.8 nm, whereby the laser beam passes the well in a vertical and concentric path. The instrument detects just linear light from the source. A clear solution gives no signal. 

The light source (1) is a 2mW vertically polarized helium-neon laser which provides a small-diameter, coherent incident beam of 633 nm wavelength which is folded back on itself via a two-prism system (2). This directs the beam toward three measuring attenuators (3, 4, 5) a calibrating/shutter attenuator (6), a condensing lens (7), the sample compartment (8) and finally, through an optical system, to the detector. 

Now suppose the object in Figure 1.2 consists of a row of small holes spaced a distance d apart in an opaque screen that is illuminated by light from a small (1 mW) helium-neon laser. This light is monochromatic, and the normals to the wavefronts (rays) are essentially parallel. Furthermore, such a light source illuminates the object coherently that is, at any instant... 

Although the first laser demonstrated was a solid state ruby laser, for many years the most common commercial systems were gas lasers such as helium neon lasers and argon ion lasers, or lasers based on organic dyes. Helium neon lasers were frequently limited in output power, argon ion lasers required expensive, sophisticated power supplies and cooling sources, and the dyes used in dye lasers were messy and often toxic. In the past decade, solid state lasers and diode lasers have become the dominant players in the commercial marketplace. 

As in the case of dispersive Raman spectrometers (cf Section 4.4.1), it is necessary to calibrate the wavelength scale of dispersive UV/VIS spectrometers. The most accurate standards for checking the UV/VIS wavelengths are lasers of various types. The inexpensive helium-neon laser can be used to check at 632.8 nm. For spectrometers with a deuterium source, spectral lines at 486.6 and 656.1 nm can be used for calibration. A common method for wavelength calibration is the use of optical filters. A filter of didymium glass has many sharp absorption peaks, which can be used as a second wavelength standard (precision within 0.5 nm). 

In such experiments information about the phonons is deduced by measurements on the spin system. With the advent of monochromatic laser sources, the technique of Brillouin scattering can be used to track phonons of definite momentum and polarization, together with the number of such phonons. Al tshuler et al. (1971, 1972) used a helium-neon laser in experiments on cerium magnesium nitrate at... 

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