Helium-neon lasers

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. ... 

The helium-neon laser is a CW gas laser which is simple and reliable fo operafe and, if fhe laser is of relatively low power, quife inexpensive. 

Figure 9.12 Energy levels of the He and Ne atoms relevant to the helium-neon laser. The number of states arising from each Ne configuration is given in a box ...

In choosing fhe examples of lasers discussed in Sections 9.2.1 to 9.2.10 many have been left ouf. These include fhe CO, H2O, HCN, colour cenfre, and chemical lasers, all operating in fhe infrared region, and fhe green copper vapour laser. The examples fhaf we have looked af in some defail serve to show how disparate and arbifrary fhe materials seem to be. For example, fhe facf fhaf Ne atoms lase in a helium-neon laser does nof mean fhaf Ar, Kr and Xe will lase also - fhey do nof. Nor is if fhe case fhaf because CO2 lases, fhe chemically similar CS2 will lase also. 

Helium-neon Helium-neon lasers Helium neon lasers Heliumpiping Helium recovery Hellebrin [13289-18-4]... 

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). 

The most familiar gas laser is the helium—neon laser (23,24). Sales of commercial helium—neon lasers exceed 400,000 units per year. The helium—neon laser is a compact package that produces a continuous beam of orange-red light. The inside diameter of the tube is commonly around 1.5 mm. The output of helium—neon lasers available commercially ranges from a fraction of a milliwatt to more than 35 mW. They have many appHcations in the areas of alignment, supermarket scanning, educational demonstrations, and holography. 

The lasers in the 670-nm region, from the aluminum indium gallium phosphide [107102-89-6] system are available at center wavelengths from 635 to 690 nm. These wavelengths He at the red end of the visible spectmm. Such lasers, which may compete for appHcations with the helium—neon laser, are under intensive development and represent less mature technology than the other lasers. 

Consumer Products. Laser-based products have emerged from the laboratories and become familiar products used by many millions of people in everyday circumstances. Examples include the supermarket scaimer, the laser printer, and the compact disk. The supermarket scanner has become a familiar fixture at the point of sale in stores. The beam from a laser is scaimed across the bar-code marking that identifies a product, and the pattern of varying reflected light intensity is detected and interpreted by a computer to identify the product. Then the information is printed on the sales sHp. The use of the scanner can speed checkout from places like supermarkets. The scanners have usually been helium—neon lasers, but visible semiconductor lasers may take an impact in this appHcation. 

C07-0124. Small helium-neon lasers emit 1.0 mJ/s of light at 634 nm. How many photons does such a laser emit In one minute ... 

The SERS spectra can be obtained on a conventional Raman spectrometer (see Figure 2). In this particular system, 632.8 nm radiation from a Helium-Neon laser is used with an excitation power of 5 mW. Signal collection is performed at 0° with respect to the incident laser beam. This coaxial excitation/collection geometry is achieved with a small prism, which is used to direct the excitation beam to the sample while allowing... 

Another technique widely used to measure the cholesteric pitch is based on the Bragg scattering of monochromatic light (obtained by a helium-neon laser) from fingerprint or planar textures of the cholesteric32 Its angular dependence is strictly related to the cholesteric pitch. 

Gas lasers, such as the helium-neon laser and the argon ion laser. 

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... 

The ADF has been measured in deoxygenated solutions with continuous excitation of either argon, krypton or helium-neon lasers. The exciting wavelengths corresponded to the bands of Sq > 1 metalloporphyrin absorption (excitation wavelengths Xex = 514.5 530.9 568.2 nm for ZnTPP and Xex = 568.2 632.8 nm for ZnTBP and CdTBP). 

Low intensity laser Helium-neon laser Lipid peroxidation Malondialdehyde... 

Yasukawa A, Hrai H, Koyama Y, Nagai M, Takakuda K (2007) The effect of low reactive-level laser therapy (LLLT) with helium-neon laser on operative wound heahng in a rat model. J Vet Med Sci 69(8) 799-806... 

Haas R, Isseroff R, Wheeland R, Rood P, Graves P (1990) Low energy helium-neon laser irradiation increases the motihty of cultured human keratinocytes. J Invest Dermatol 94 822-826... 

Abou Hashieh I, Tardieu C, Franquin JC (1997) Helium neon laser irradiation is not a stressful treatment A study on heat-shock protein (HSP70) level. Lasers Surg Med 20 451-460... 

Barasch A, Peterson D, Tanzer J, D Ambrosio J, Nuki K, Schubert M, Franquin J, Clive J, Tutschka P (1995) Helium-neon laser effects on conditioning-induced oral mucositis in bone marrow transplantation patients. Cancer 76(12) 2550-2556... 

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