Lasers performance

Several heterostructure geometries have been developed since the 1970s to optimize laser performance. Initial homojunction lasers were advanced by the use of heterostmctures, specifically the double-heterostmcture device where two materials are used. The abiUty of the materials growth technology to precisely control layer thickness and uniformity has resulted in the development of multiquantum well lasers in which the active layer of the laser consists of one or mote thin layers to allow for improved electron and hole confinement as well as optical field confinement. 

Various designs for dye lasers, with different pumping sources and geometries, resonator configurations, and flow systems, have been successfully used to optimize laser performance. 

The photochemical experiments with lasers performed up to now may therefore be subdivided into three categories according to which one of these laser features was used in the investigation. 

An intercomparison of the mass spectrometer method with an LIF instrument, however, was not as good. While the slope of the plot of LIF versus the MS measurements was 0.73, the r value was only 0.26, in part due to poor laser performance in the LIF instrument during the studies (Mather et al., 1997). 

This brief Datareview reviews different types of defect that influence diode laser performance and speculates on how GaN diode lasers have seemingly avoided their detrimental influences. 

In order to determine the influence of various discharge processes on laser characteristics, gas temperature, electron density, and average electron energy were taken as independent modeling parameters [8]. In reality this cannot be achieved under ordinary dc discharge conditions. However, by using this approach it is possible clearly to identify the discharge parameters that have major influence on laser performance characteristics. 

One additional point of importance that should be noted is that helium plays an important role as a relaxant in determining the population of the (100) level and, therefore, gain. The importance of He as a lower level relaxant can best be appreciated by noting the early work of Moeller and Rigden [70] in which a factor of 5 enhancement in laser performance was achieved through addition of helium to the system. In subsequent work, Witteman [71] demonstrated the effectiveness of water vapor in place of He as a relaxant for the lower laser level. 

Additional evidence which shows that the deuterium enhancement of laser performance is not principally caused by an increased efficiency of the transfer of energy from ligand to europium ion is provided by the data in Table IV which show that the already short lifetime of the triplet state in the gadolinium chelate is not at all changed by deuteration of the ligand or solvent. 

The dependence of intramolecular proton transfer on solvent friction has been established for 2-(2 -hydroxy-5-methylphenyl) benzotriazole in alcohol and other solvents. Excited-state proton transfer in 2-(2 -hydroxyphenyl) benzothiazole has also been studied 2 Photophysical properties and laser performance of w, w -bis ( oxazol-2-yl)- -oligophenylenes in dioxane have been measured at room temperature. +p increases with the number of phenyl rings between terminally positioned oxazoyl groups. 

An application in photomedical research is the measurement of absorption and transmission of thick specimens e.g. human skin. A spectral narrowband irradiation of skin lesions and tumors can use the high spectral intensity together with the tunability of special lasers. Action spectra of phototherapeutic interest such as of photosensitizers like psoralens can be investigated. Furthermore, tunable lasers perform a selective excitation of practically any quantum state of atoms or molecules in the wavelength range from about 200 nm to 20 p. 

Sugawara M., Mukai K. and Shoji H. (1997), Effect of phonon bottleneck on quantum-dot laser performance , Appl. Phys. Lett. 71,2791-2793. 

Tb, Nd andPr " ions have been investigated as activator ionsinCeF3 2 h Energy transfer has been observed by both radiative and radiationless processes from the host (Ce " ) to excited states of these activators. The details of the kinetics and the mechanism of the transfer have not been determined. Delayed fluorescence has been observed from the F3 2 Isvel of Nd " and attributed to slow radiationless relaxation processes in the excited states ). Energy transfer can also occur from the low lying F7/2 host level to the In/2 state of Nd or the Hs state of Pr ". In the former case this affects the population of the terminal state of the lasing transition and thus can alter laser performance characteristics. 

Army Laser Systems. Lasers perform a variety of functions and come in many shapes and forms. Dangerous lasers can be smaller than a pen or larger than a truck and every size and shape in between. Table 6-C lists several army-fielded systems. Several systems, such as the AN/VVG-2, are almost entirely phased out of the US Army inventory. They may, however, be found in foreign militaries or in National Guard or reserve units. The Nominal Ocular Hazard Distance and the Optical Distance should only be used as a general guide. Specific questions need to be addressed to the USACHPPM. 

Figure C2.16.ll. Changes in the threshold current density of diode lasers resulting from new structure concepts. A homojunction diode laser was first demonstrated in 1962. SH and DH stand for single and double heterostructure, respectively. The best laser performance is now obtained in quantum well (QW) lasers.

Figure 29. Laser performance parameter chart. Modified after Payne et al. (1994).

Surface Characterization. Most modem techniques for the characterization of surfaces have been developed since 1970 (74,75). Surface techniques allow for both qualitative and quantitative characterization of trace levels of molecular species (see Surface AND INTERFACE ANALYSIS). Most recently an extension of surface analysis utilizing laser ionization has been introduced (76). In surface analysis by laser ionization (sah), a probe beam, composed of ions, electrons, or laser light, is directed to the surface under examination to remove a sample of material. An untuned, high intensity laser passes dose to, but paralld and above the surface. The laser has sufficient intensity to induce a high degree of nonresonant, and hence nonselective, photoionization of the vaporized sample of material within the laser beam. The nonselectively ionized sample is then subjected to mass spectral analysis to determine the nature of the unknown species. A highlight of this technique is the use of efficient, nonresonant, and therefore nonselective photoionization by pulsed imtuned laser radiation. The commercial availabiUty of intense laser radiation makes this technique viable. The mass spectrometer, not the laser, performs the chemical differentiation. 

H. Yagi, T, Yanagitani, K, Takaichi, K. Ueda, A.A. Kaminskii, Characterizations and laser performances of highly transparent Nd iYsAlsOii laser ceramic, Opt. Mater., 29, 1258-62 (2007). 

Fabrication and Laser Performance of (Ybo o5Yo.95-xLax)203 Ceramics... 

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