Laser emission

By varying the types of gases inside the cavity, the wavelength of the laser emission can be varied (Table 18.3). These gas lasers are useful because the emitted light lies mostly in the ultraviolet... 

A third pumping method (Fig. Ic) uses an electrical discharge in a mixture of gases. It relies on electronic excitation of the first component of the gas mixture, so that those atoms are raised to an upper energy level. The two components are chosen so that there can be a resonant transfer of energy by collisions from the upper level of the first component to level 3 of the second component. Because there are no atoms in level 2, this produces a population inversion between level 3 and level 2. After laser emission, the atoms in the second component return to the ground state by collisions. 

Electronic excitation from atom-transfer reactions appears to be relatively uncommon, with most such reactions producing chemiluminescence from vibrationaHy excited ground states (188—191). Examples include reactions of oxygen atoms with carbon disulfide (190), acetylene (191), or methylene (190), all of which produce emission from vibrationaHy excited carbon monoxide. When such reactions are carried out at very low pressure (13 mPa (lO " torr)), energy transfer is diminished, as with molecular beam experiments, so that the distribution of vibrational and rotational energies in the products can be discerned (189). Laser emission at 5 p.m has been obtained from the reaction of methylene and oxygen initiated by flash photolysis of a mixture of SO2, 2 2 6 (1 )-... 

Fig. 11. Schematic of edge-emitting laser diodes where the arrows represent the direction of laser emission and U represents the active region (a) standard stmcture with cleaved facets for mirrors and (b) distributed feedback (DFB) laser that employs coherent reflection from a grating to generate optical...

Sensitivity can be improved by factors of 10 using intracavity absorption, placing an absorber inside a laser resonator cavity and detecting dips in the laser emission spectmm. The enhancement results from both the increased effective path length, and selective quenching of laser modes that suffer losses by being in resonance with an absorption feature. 

Figure 10-15. Output vs. input energy characteristic of our laser device. The horizontal dashed curve indicates the zero line. A clear laser threshold behavior at an excitation pulse energy ol 1.5 nJ is observed. Below the lasing threshold only isotropic phololuminesccncc is entitled. Above threshold the device emits low divergence single mode laser emission perpendicular to the surface, as schematically shown in the inset. The laser light is polarized parallel to the grating lines.

G. Wegmann, H. Giessen, D. Herlel, R.F. Mahtl, Blue-green laser emission from a solid conjugated polymer, Sol. Stat. Comm. 1997, 104, 759. 

A. Schulzgen, C. Spiegelberg, M.M. Morrell, S.B. Mendes, B. Kippclcn, N. Peyghatnbarian, M. F. Nabor, E. A. Mash, P. M. Allcmand, Near diffraction-limited laser emission from a polymer in a high finesse planar cavity, Appl. Phys. Leu., 1998, 72, 269. 

F. Hide, B.J. Schwartz, M. A. Diaz-Garcia, A.J. Hceger, Laser emission from solutions and films containing semiconducting polymer and titanium dioxide naiioerysials. Chem. Phys. Lett. 1996, 256, 424. 

N. Karl, Laser emission from an organic molecular crystal, Physit o Stums Solidi A 1972, 13, 651. 

The applied field E is a periodic function of time t and has a frequency i o which is the frequency of laser emission. 

This manuscript describes the dendritic macromolecules for optical and optoelectronic apph-cations, particularly stimulated emission, laser emission, and nonlinear optics. Dendrimers have been designed and synthesized for these applications based on simple concepts. A coreshell structure, through the encapsulation of active imits by dendritic branches, or a cone-shaped structure, through the step-by-step reactions of active imits, can provide particular benefits for the optical high-gain media and nonlinear optical materials. It also described experimental results that support the methods presented for designing and fabricating functionalized dendrimers for optoelectronic applications, and theoretical results that reveal the intermolecular electronic effect of the dendritic structure. 

Keywords. Core-shell structure. Cone structure. Laser emission. Nonlinear optical property... 

Stimulated Emission and Laser Emission from Dendrimer Media. .. 211... 

Fig. 6. Laser emission spectrum from DCM/dendrimer solution in cuvette. Inset schematically illustrates experimental setup...

One of the main characteristics of the laser emission is the huge amount of energy that is concentrated within a narrow beam and can be delivered on a tiny area. In order to take full profit of the high power density available, it is also necessary to use photosensitive systems which obey the reciprocity law, i.e. where the energy required for the reaction is not dependent on the light intensity, which means that the quantum yield remains constant. This condition appears to be almost fullfilled in the present case since the fluence, expressed in J cm-2, was found to increase by only a factor of 4 when the light-intensity was increased by over 4 orders of magnitude (Table I). 

The spectral resolution of the most monochromatic laser yet devised, expressed as frequency of the laser emission divided by the laser linewidth, is approximately 5 x 10. The laser in question is a special-purpose He-Ne laser with a nominal wavelength of 632.8 nm (15,308 cm l or 4.74 x 10 Hz in frequency units) and a linewidth of 7 to 10 Hz. It is difficult to grasp the physical significance of this degree of resolution. One illustration is that, if the spectrum of this laser were displayed on chart paper such that the zero of electromagnetic energy were located at the sun and 15,308 cm l were located at the orbit of Earth, the width of the peak representing the output of the laser would be 3 millimeters. 

Bis( 1,2-dithiolene) complexes are generally thermally and photochemically very stable, and their Vis-NIR absorption can be tuned in order to reach the wavelength ranges of interest for NIR lasers, such as Nd YAG, Nd YLF, and Er Glass solid-state lasers (emission wavelengths A.em = 1064, 1053, and 1540 nm, respectively). In this context, many groups of researchers have devoted their efforts to synthesising 1,2-dithiolene complexes for this type of application, and indeed some of them have been patented and are commercially... 

Fig. 19.1 An optofluidic laser based on the OFRR. (a) SEM picture of the OFRR cross section. The wall thickness is 5 pm. (b) Side view of the OFRR laser. The pump laser is focused on the capillary and the OFRR laser emission can be out coupled through a waveguide. Reprinted from Ref. 18 with permission. 2008 Optical Society of America...

Fig. 19.3 Optofluidic laser setup (cross section view) fiber taper is used to evanescently couple out the laser emission...

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