Laser helium

Cadmium-helium laser See Helium-Cadmium laser. 

Figure Cl. 1.1. Schematic of a typical laser vaporization supersonic metal cluster source using a pulsed laser and a pulsed helium carrier gas.

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. ... 

Brightness. This is defined as the power emitted per unit area of the output mirror per unit solid angle and is extremely high compared with that of a conventional source. The reason for this is that, although the power may be only modest, as in, for example, a 0.5 mW helium-neon gas laser, the solid angle over which it is distributed is very small. 

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. 

Laser action fakes place befween excifed levels of fhe neon atoms, in a four-level scheme, fhe helium atoms serving only fo mop up energy from fhe pump source and fransfer if fo neon atoms on collision. The energy level scheme is shown in Figure 9.12. 

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 an excimer laser the mixture of inert gas, halogen gas, and helium, used as a buffer, is pumped around a closed system consisting of a reservoir and the cavity. 

Decay of the 1 and 2 lower levels of the laser transitions are rapid down to the 2 level this is depopulated mostly by collisions with helium atoms in the CO2 N2 Fie gas mixture which is used. 

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. 

Figure 9.46 shows an example of a fluorescence excitation spectmm of hydrogen bonded dimers of x-tetrazine (1,2,4,5-tetraazabenzene). The pressure of x-tetrazine seeded into helium carrier gas at 4 atm pressure was about 0.001 atm. Expansion was through a 100 pm diameter nozzle. A high-resolution (0.005 cm ) dye laser crossed the supersonic jet 5 mm downstream from the nozzle. 

Argonaut Argon difluoride Argon fluoride Argon-helium Argon ion lasers Argon-oxygen... 

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 helium—ca dmium laser, which has emission at 0.442 and 0.325 p.m, is a somewhat different type of ionized gas laser (28). It operates using the ionized states of cadmium, produced by heating ca dmium in a furnace. The output of continuous, commercially available helium—ca dmium lasers ranges up to 150 mW. 

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. 

---