Gain 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]. 

All lasers have the following three fundamental components (see Figure 1). The gain medium, the business end of the laser, is the medium in which excited states are created which will produce stimulated emission. The exciter is the source of energy for production of the excited states in the gain medium. Finally, the optical resonator determines the directionality, wavelength selectivity, optical feedback, polarization, and other characteristics of the stimulated emission from the gain medium. 

A number of points are clear. First, in all cases the major expense of laser photons is the hardware, not the energy (even at Austin prices). Secondly, the intrinsically greater efficiency of the lower-energy lasers, especially the economic attractiveness of the CO2 laser, is evident. One can easily understand why laser chemistry schemes based upon multiphoton infrared absorption attract so much effort. Thirdly, on a per-unit-time basis the ion laser is more than twice as expensive to operate than even the rather exotic excimer laser. This is because of the inherent energetic inefficiency of the rare-gas plasma as a gain medium and because of the extrinsic, and hideous, expense of ion laser plasma tubes (and their poor reliability). 

In an OFRR, WGMs reside in both core and wall. Therefore, only a fraction of the WGM interacts with the gain medium. The lasing behavior of this partially interacting system has been analyzed by Moon et al.10 For a given dye concentration, the minimum fraction of the excited molecules, y(X), is given by ... 

In the OFRR, the wall thickness is important, as it determines the fraction of the light in the core that interacts evanescently with the gain medium when the solvent is of low RI. To precisely characterize the OFRR thickness noninvasively, we use the method developed previously22, in which various concentrations of water-ethanol mixtures are passed through the OFRR, and the WGM spectral shift in response to RI changes in the core is plotted as demonstrated in Fig. 19.4b. By matching the experimental sensitivity results with those obtained from our... 

A pumping mechanism, in order to excite the atoms or molecules of the gain medium by supplying them with sufficient energy. 

The key prerequisite for optical amplification via stimulated emission is that the emitted photons propagate through the gain medium long enough to initiate further stimulated transitions. This condition can be expressed as... 

Principal components of a laser (1) Gain medium (gas, liquid, or solid crystal, e.g,. ruby) inside the optical cavity, (2) input pumping energy (e.g., from flash lamp), (3) high-efficiency reflector ( 100% reflectivity), (4) low-efficiency mirror, that is, output coupler ( 95% reflectivity), (5) output laser beam. Components (3) and (4) form the optical cavity, also known as a Fabry-Perot interferometer. 

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