The helium-neon laser

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. 

The ground configuration of Ne is ls 2s 2p, giving a sfafe. The excifed configurations give rise fo sfafes fo which fhe Russell-Saunders approximation does nof apply. Nevertheless, any. .. 2p ns or. .. 2p np configuration, wifh n 2, gives rise fo four or fen sfafes, respectively, as would be fhe case in fhe Russell-Saunders approximation (see 

The states arising from the. .. Ip Ss configuration of Ne have very nearly the same energy as that of the 2 Sq state of He so that collisional energy transfer results in efficient population of these Ne states. Similarly, the states arising from the. .. configuration 

Infrared laser lines involving. .. 2p 5s —. .. 2p 4p transitions in the 3.39 pm region are not particularly usefiil. However, they do cause some problems in a 632.8 nm laser because they deplete the populations of the. ., 2p 5s states and decrease the 632.8 nm intensity. The 3.39 pm transitions are suppressed by using multilayer cavity mirrors designed specifically for the 632.8 nm wavelength or by placing a prism in the cavity orientated so as to deflect the infrared radiation out of the cavity. 

Decay from the. .. 2p 3p states to the. .. 2p 3s states is rapid but the. .. 2p 3s states are relatively long-lived. Their populations tend to build up and this increases the probability of the. .. 2p 3p 2p 3s radiation being reabsorbed, a process known as radiation 

One of the mirrors forming the laser cavity is as close to 100% reflecting as possible (99.5%) the other is coated to allow 1% of the radiation to emerge as the laser beam. 

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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 ...

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. 

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

The Helium-Neon Laser-Induced Fluorescence Spectrum of Molecular Iodine 14... 

Polyethylene. The Raman spectrum of polyethylene has been known for some years and all the bands have been identified seemingly unambiguously. Recently the spectrum has been recorded using stretched large-diameter fibres as a sample. The spectra were recorded with the fibre bundled vertically, horizontally and end-on in a Cary 81 spectrometer. The arrangements are illustrated in Fig. 3. The electric vector of the helium-neon laser is set vertically and therefore in the first orientation (a), the fibre axis and electric vector are parallel. 

Helium To provide an inert atmosphere for welding As a coolant in nuclear reactors With 20% oxygen, as a breathing gas for deep-sea divers To inflate the tyres of large aircraft To fill airships and weather balloons (Figure 11.12) In the helium-neon laser In low-temperature research, because of its low boiling point... 

Another common laser class is that of gas lasers, which includes helium neon (HeNe) lasers, carbon dioxide (CO2) lasers, nitrogen lasers, and so on. The helium neon laser, widely used until the advent of the diode laser, was one of the first types developed and commercialized. As described above, it is a discharge-pumped gas laser, which generally produces an output measuring a few mW in power. 

Of greater interest in chemistry are lasers in which the active medium is a gas. The most common and least expensive gas laser is the helium-neon laser, which uses a mixture of 85% He and 15% Ne at pressures of the order of 10 torr. An energy-level diagram is shown in Fig. 14.14. An electric discharge excites He atoms to their H 25- S and S states, 19.8and20.6eV above the ground state. This energy... 

Gas Lasers. A variety of ga.s lasers is available commercially. These devices are of four types (1) neutral atom lasers such as He-Ne (2) ion lasers in which the aciive species is Ar or Kr (3) molecular lasers in which the lasing medium Is CO, or Nil and (4) excimer lasers. The helium-neon laser is the most widely encountered of all lasers because of its low initial and maintenance costs, its great reliability, and its Kivv H)wcr consumption. The nuist important of its output lines is at 6.32.8 nm. It is generally operated in a continuous mode rather than a pulsed mode. 

In contrast to the setup shown in Figure 5, our experiment uses two coaxial laser beams focused onto the sample C by a lens L (Figure 7). The dye laser beam (power 1 to 10 mW) creates the thermal lens in the sample, whereas the helium-neon laser is used only for monitoring development of the thermal lens. To avoid a thermal lens being induced by the helium-neon laser, a neutral density filter F2 reduces the power of its beam to 6 to 7 /xW in the sample. In front of the detector D, an interference filter F, blocks the beam of the dye laser, and a pinhole P is placed such that only light near the optical axis reaches the detector. To monitor the wavelength of excitation Ao, part of the dye laser beam is deflected by a glass plate Gj onto a... 

Another important advantage of FT-IR spectrometers is their outstanding frequency accuracy (Connes advantage), the basis for all achievements in difference spectroscopy. This accuracy of spectral frequencies is due to the precise and stable collection of the interferogram signal, triggered by the helium—neon laser. An accuracy in wavenumber of better than 0.01 cm can be achieved. 

Stone JA, Decker JE, Gill P, Juncar P, Lewis A, Rovera GD, Viliesid M (2009) Advice from the CCL on the use of unstabilized lasers as standards of wavelength the helium-neon laser at 633 nm. Metrologia 46(1) 11-18... 

Figure 1 depicts the optofluidic circuit that is connected to the helium-neon laser. The aperture is filled with black ink to reduce the divergence of the laser beam. The microfluidic circuit comprises of the core fluid inlet, two cladding fluids, and two fluidic outlets. The core fluid inlet is injected with calcium chloride, while the cladding fluids are injected with distilled water. All the fluids flow out of the microfluidic circuit via... 

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