Laser medium

In this section, we describe a simple laser setup using a high-gain medium consisting of DCM-encapsulated dendrimers in a methanol solution. The results can be applied to a solid-state laser medium [42], described in the next section. In that case, we used RdB-dendrimer in the waveguide gain medium [43]. 

Optically-pumped lasers (OPLs) offer very useful power levels at discrete frequencies well into the THz band. Most OPLs comprise some sort of gas cell, which is the active laser medium, that is pumped by a carbon dioxide laser. These devices are inherently inefficient because the... 

A laser medium in a tube within the laser cavity, with a mirror at each end. A pump source must excite the atoms or molecules in the laser medium so that stimulated emission (Figure 1.3(b)) can occur. Lasers are classified by the nature of the medium, important ones being ... 

Dye lasers, in which the laser medium is a coloured fluorescent dye dissolved in a nonabsorbing solvent. 

The small divergence of the laser beam, which is limited only by diffraction and by optical inhomogeneities of the laser medium or other optical components in the laser cavity, has several advantages for spectroscopists ... 

The wavelength of a laser line, however, is determined by two factors the fluorescence profile of the corresponding transition in the laser medium and the eigenfrequencies of the laser resonator modes. At normal multimode operation of a laser, where many axial and transverse modes participate in laser oscillation, these eigenfrequencies cover the whole spontaneous line profile nearly uniformly. 

The last two chapters discussed spectroscopic studies which used coincidences between laser lines and transitions in other atoms or molecules. These investigations have been performed either with lasers as external light sources, or inside the laser cavity. In the latter case coupling phenomena occur between the absorbing species and the laser emission, one example of which is the saturation effect employed in Lamb dip spectroscopy and laser frequency stabilization. This chapter will deal with spectroscopic investigations of the laser medium itself and some perceptions one may obtain from it. 

Various component cooling schemes were proposed and used, but a major improvement was made when the concept of cooling a flowing laser medium was proposed, thereby taking advantage of the far more effective cooling hy convection lhan by conduction. Gas lasers were considered the most apt for application of this concept and this led to the gas dynamic laser.1... 

In a Q-switched laser, the population inversion, usually produced in the same way as CW operation, builds up by making the cavity quality factor Q unfavorable for lasing. Then, when the pump energy stored in the laser medium is at the desired level, the Q is suddenly adjusted (electro- or acousto-optically) to release the pulse. This results in high peak powers. 

In laser measurements on hydrogen halides, the system under investigation is itself all, or part, of the active laser medium. Similar experiments have not yet been made on other molecules. However, in related experiments on CO, in the author s laboratory [242,432] and elsewhere [433], a CO cw laser has been used to probe the vibrational distributions in a reaction system outside the optical cavity that may act as an amplifier or absorber of lines from the laser. Time-resolved observations can be made for as long as one chooses after the reaction is initiated. If tunable infrared lasers become readily available this technique is likely to be applied more widely. 

Lasers have three primary components (Fig. 4) 1) an active medium that amplifies incident electromotive waves 2) an energy pump that selectively pumps energy into the active medium to populate selected levels and to achieve population inversion and 3) an optical resonator, or cavity, composed of two opposite mirrors a set distance apart that store part of induced emission concentrated in a few resonator modes. A population inversion must be produced in the laser medium, deviating from the Boltzman distribution thus, the induced emission rate exceeds the absorption rate, and an electromotive wave passing through the active medium is amplified rather than attenuated. The optical resonator causes selective feedback of radiation emitted from the excited species in the active medium. Above a pump threshold, feedback converts the laser ampler to an oscillator, resulting in emission in several modes. 

In Figure 20.19 we sketch the operation of the neodymium-YAG laser. The laser medium is a crystal of yttrium-aluminum-garnet doped with neodymium ions. This laser has the advantage over the ruby laser that the laser action occurs between two excited states, and the population inversion is consequently easier to maintain. The Nd-YAG laser is widely used in science and technology. One major application is to pump the so-called dye lasers in which the medium is intensely colored dye molecules (usually with conjugated double bonds) dissolved in... 

FIGURE 22.24 (a) In this solid-state laser, photons emitted as electrons and holes recombine to stimulate the emission of additional photons, (b) Reflection by a mirror on the right side sends coherent waves back through the laser medium, (c) Further amplification occurs by stimulated emission, (d) Some of the waves pass through a partially reflecting mirror on the left side. 

Fig. 68. Three- and four-level scheme of a laser medium.

Population inversion cannot be achieved in a two-level system, a material with two electronic states. At best, a nearly equal population of the two states is reached, resulting in optical transparency, when absorption by the ground state is balanced by stimulated emission from the excited state. An indirect method of populating the emitting excited state must be used. In a three-level laser (Figure 3.6, left), irradiation of the laser medium pumps an upper level 2, which is rapidly depleted by a nonradiative... 

Laser Medium 7/nm (fundamental) Optical power or Pulse duration ... 

Vision impaired. Large dark spot at or near center of vision. External exam normal. Internal exam foveal retinal lesion(s). Peri-foveal retinal butn, and/or hemorrhage (visible or near-infrared laser, medium dose). Evacuate. Needs physician/PA evaluation. 

GaAlAs - Gallium -Aluminum -Arsenide (LASER medium). 

Nd YAG - Neodymium Yittrium -Aluminum -Gamate (LASER medium). 

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