Lasing action

V.G. Kozlov, V. Bulovic, P.E. Burrows, M. Baldo, V.B. Khalfin, G. Pailhasarathy, S.R. Forrest, Y. You, M. E. Thompson, Study of lasing action based on Forster energy transfer in optically pumped otganic semiconductor thin films, J. Appl. Phys. 1998, 4, 4096. 

We have studied, theoretically and experimentally, the characteristics of a novel class of lasers that are based on radial Bragg reflectors. Lasing action with low threshold levels are demonstrated at room temperature under pulsed optical pumping. The observed Q factors are in the order of several thousands. The unique characteristics on these lasers make them promising candidates for numerous applications in telecommunications, sensing, and basic research. 

A second measurement series illustrates the lasing action of the dye droplet, where consecutively loaded droplets are pumped at different average pump power. The measured spectra shown in Fig. 17.7 show the dye droplet output power vs. pump power. In the measurement sequence, the pump power was first increased from 150 to 900 mW and subsequently decreased again. The reproducibility of the obtained spectra and the lasing threshold are seen from Fig. 17.7, respectively. The experiments reveal no significant indication of neither bleaching nor evaporation. 

The first report of lasing action (600 nm) in the solid state involved the use of MEH-PPV as a blend with dispersed nanoparticulate TiOj, which acted as scatterers to achieve lasing. This was quickly followed by the first non-blended, microcavity laser, using PPV, that could support high current densities. To date a whole range of... 

Emerald, Cr " doped beryl, has a beryl structure with the Cr " impurity ions in highly distorted octahedron sites. The discovery of lasing action in emerald stimulated investigation of its luminescence properties. It was established that its tuning range is approximately 730-810 nm, while luminescence consists of a narrow line at 684 nm and a band peaking at 715 nm with similar decay times of 62 ps. The relative intensities of those line and band are different in a- and 7T-polarized spectra (Fabeni et al. 1991). 

The potential lasing action of rare earth diketonates has been studied [203]. The complexes Ln( 1,3-diketone) tend to add on one or more ligands such as water. Dehydration of the hydrated complexes leads to decomposition or formation of polymeric... 

A third and important requirement for lasing action is to have sufficient optical gain irrespective of the active medium. The optical gain is achieved by multiple passes of the photons through the population-inverted medium. Multiple passes of photons is achieved by placing the active medium in an optical resonator. The optical resonator consists of two or more mirrors. A typical optical arrangement for a laser system is shown in Fig. 12.13. 

Lasing action has been observed with other rare earths. The lower laser level in holmium is close to the ground state and can operate as a four level laser at liquid nitrogen temperatures. Erbium is similar to holmium. With other rare earths, alternate wavelengths can be obtained. Both Ho and Er operate in a region greater than 1.5 pm. Erbium can also... 

The lasing action of Nd3+ ion in YAG or glass is well known and Sm is used in glass surrounding lasing rods to absorb unwanted UV light. 

Since it has been shown that in many exothermic reactions a large part of the energy liberated enters the vibration of the newly formed molecule, there has been considerable interest in developing vibrational lasers pumped by chemical reaction. Although a total inversion between vibrational states is not required [223], it is difficult to reach the threshold condition for lasing action if relaxation is faster than excitation by reaction. These effects can be reduced where a light flash (or pulsed discharge) initiates reaction, and stimulated emission has now been observed from a number of systems [224]. 

Stimulated emission That part of the emission which is induced by a resonant perturbing electromagnetic field. The transition between states, n and m, is governed by the Einstein coefficient of stimulated emission, Bnm- CIDNP emission and lasing action are examples of processes which require stimulated emission. 

Population inversion is often achieved by a multi-level atomic or molecular system in which the excitation process, called pumping, is accomplished by electrical means, by optical methods, or by chemical reactions. In some cases, the population inversion can be sustained to produce a continuous wave (CW) output beam that is continuous with respect to time. In other cases, the lasing action is self terminating, so that the laser is operated in a pulsed mode to produce a repetitive pulse train or a single-shot action. ... 

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