Random laser

Amplified Spontaneous Emission Superradiance and Superfiuorescence Cavity-Based Lasers Random Lasers Experimental Setup for Studying Laser Action... 

In the previous section we discussed light and matter at equilibrium in a two-level quantum system. For the remainder of this section we will be interested in light and matter which are not at equilibrium. In particular, laser light is completely different from the thennal radiation described at the end of the previous section. In the first place, only one, or a small number of states of the field are occupied, in contrast with the Planck distribution of occupation numbers in thennal radiation. Second, the field state can have a precise phase-, in thennal radiation this phase is assumed to be random. If multiple field states are occupied in a laser they can have a precise phase relationship, something which is achieved in lasers by a teclmique called mode-locking Multiple frequencies with a precise phase relation give rise to laser pulses in time. Nanosecond experiments... 

Adsorbed atoms and molecules can also diflfiise across terraces from one adsorption site to another [33]. On a perfect terrace, adatom diflfiision could be considered as a random walk between adsorption sites, with a diflfiisivity that depends on the barrier height between neighbouring sites and the surface temperature [29]. The diflfiision of adsorbates has been studied with FIM [14], STM [34, 35] and laser-mduced themial desorption [36]. 

Closs G L and Miller R J 1979 Laser flash photolysis with NMR detection. Microsecond time-resolved CIDNP separation of geminate and random-phase polarization J. Am. Chem. Soc. 101 1639—41... 

A progression with v = 2, illustrated in Figure 7.18, can be observed only in emission. Its observation could result from a random population of v levels or it could be observed on its own under rather special conditions involving monochromatic excitation from v" = 0 to if = 2 with no collisions occurring before emission. This kind of excitation could be achieved with a tunable laser. 

Although 0-switching produces shortened pulses, typically 10-200 ns long, if we require pulses in the picosecond (10 s) or femtosecond (10 s) range the technique of mode locking may be used. This technique is applicable only to multimode operation of a laser and involves exciting many axial cavity modes but with the correct amplitude and phase relationship. The amplitudes and phases of the various modes are normally quite random. 

The time period A/ia which the light wave undergoes random changes is called the coherence time. It is related to the Hnewidth Av of the laser by the equation... 

Andrews, L.C., Phillips, R.L., Laser beam propagation through random media, SPIE, Bellingham, 1998... 

A laser consists in a medium where stimulated emission dominates over spontaneous emission placed inside an optical cavity which recycles the optical field. Above threshold, the photon number probability density distribution is poissonian, that means that the photon arrival time are a random variable. The probability of obtaining m photons during a given time interval is thus... 

Amino acid sequences of eleven homologous sea anemone polypeptides have been elucidated. All possess three disulfide bonds. The six half-cysteine residues always occur in the same positions (7,8). Initial studies concerning the toxin secondary and tertiary structures relied upon circular dichroism, laser Raman, and, to a lesser extent, fluorescence spectral measurements (15—18). The circular dichroism spectra of the four toxins so far examined are essentially superimpos-able and thus indicate a common secondary structure. The only peak observed, a negative ellipticity at 203 nm, largely results from a non-regular ("random")... 

The random laser is a simple optical system in which the strong optical scattering in the random medium forms an optical recurrent path. Recent reports on random lasers have described the emission of laser light by metal-oxide polycrystalline and micrometer-sized particles [46]. Because of its structural simplicity and small size, the single random laser is a promising miniature light source for optical devices, such as waveguides and optical switches. 

Scanning electron microscopy, light microscopy, and confocal laser scanning microscopy together with FISH Randomly amplified polymorphic DNA (RAPD), Enterobacterial repetitive intergenic consensus sequence (ERIC-PCR)... 

Sun it surface - A total of 39 laser pulses were applied essentially at random to the sunlit host glass surface. 

Sutton CJ, Ewen SP, Whitelaw N (1994) Prospective, randomized double-blind controlled trial of laser laparoscopy in the treatment of pelvic pain associated with minimal, mild and moderate endometriosis. Fertil Steril 62 696-700... 

Considering that J 2 I 2 and that the ionization rates at R = Rq have little 9 dependence [35], the dominant difference should be due to the electron and nuclear dynamics in the steps 2 and 3. The observed single molecule responses are obtained by superposing the radiation from all the molecules with random orientation coherently. For linearly polarized laser field, whose direction is defined as x axis, the observed dipole moment is given by... 

Because the laser is fired independently from the electric activity in the clouds, and because natural electric activity in clouds is a random process, temporal correlations between the electric events detected by the LMA and the laser operation were used as an evidence for an effect of the laser. At each location, the events synchronized (within 2 ms) with the laser have been identified. The probability async that these events may have been obtained by chance among random events, rather than being due to an effect of the laser, was estimated. async can be understood as the risk of error when concluding that the observed pulses are related with the laser pulses. This corresponding confidence level is therefore 1 — async-... 

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