Optical feedback, lasers

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. 

All these waveguiding films lack one important feature that would be necessary for true lasing They do not have a resonator for optical feedback that would lock the optical modes traveling in the gain direction. The thin-film waveguide confines the optical modes in one direction (in the vertical), but in the other two dimensions the modes have translational and rotational symmetry. The incorporation of resonator structures into the thin films in order to get true organic solid-state lasers will be described next. 

The emission linewidth of LEDs is typically 10 nm, which is quite broad in comparison to that achievable with laser diodes. Narrower linewidths down to ca. 0.9 nm can be obtained using resonant cavity LEDs.(61) Superluminescent LEDs have been produced with low spectral ripple (less than 10% at wavelengths down to 670 nm) by suppressing the optical feedback in laser diode junctions.(62)... 

Wyatt and Phillips (1972) commercialized an electrostatic balance with electro-optic feedback control and light-scattering capabilities the device is shown in Fig. 2. The dc field was generated by a lower electrode and an electrified pin mounted in the upper plate. The particle was illuminated by a laser beam, and light scattered from the particle hit the edge of an adjustable... 

Since the photophoretic force depends on the electromagnetic absorption efficiency Q y , which is sensitive to wavelength, photophoretic force measurements can be used as a tool to study absorption spectroscopy. This was first recognized by Pope et al. (1979), who showed that the spectrum of the photophoretic force on a 10 foa diameter perylene crystallite agrees with the optical spectrum. This was accomplished by suspending a perylene particle in a Millikan chamber with electro-optic feedback control and measuring the photophoretic force as a function of the wavelength of the laser illumination. Improvements on the technique and additional data were obtained by Arnold and Amani (1980), and Arnold et al. (1980) provided further details of their photophoretic spectrometer. A photophoretic spectrum of a crystallite of cadmium sulfide reported by Arnold and Amani is presented in Fig. 11. 

In the work by Hales and co-authors [83] the prehistory distribution was observed experimentally using a semiconductor laser with optical feedback. Near the solitary threshold, the system was unstable after a period of nearly steady operation, the radiation intensity decreased then it recovered comparatively quickly, growing to regain its original value decreased again and the cycle repeated. In the experiment, the output intensity was digitized with 1 ns resolution. The pi, obtained in [83] from 1512events is shown in Fig. 9. The results were compared with the results of numerical simulation for the system (17). 

Fig. 3. (a) Spectral power density of the beat note between the extended-cavity master laser and the slave laser, with or without optical feedback (b) Spectral power density of the beat note between the two phase-locked diode lasers... 

Laser-diode feedback. This detection technique utilizes the great sensitivity of lasers to optical feedback and is used to detect movement of the cantilever. Laser light reflected off the back of the cantilever is returned back into the laser 120 -22],... 

A laser is a radiation source which produces a very high spectral radiance in a small spectral range at a fixed wavelength. A laser combines a radiation source with spectral isolation of its radiation - two important components of a spectrometer. The word laser is an acronym which stands for light amplification by stimulated emission of radiation. The essential elements of a laser are an active medium a pumping process to produce a population inversion and a suitable geometry or optical feedback elements (Moore et al., 1993). Most lasers are essentially Fabry-Perot interferometers whose cavities contain... 

C. Masoller. Anticipation in the synchronization of chaotic semiconductor lasers with optical feedback. Phys. Rev. Lett., 86 2782, 2001. 

M. Wolfrum and D. Turaev. Instabilities of lasers with moderately delayed optical feedback. Opt. Commun., 212 127-138, 2002. 

We have used a femtosecond-written Nd YAG ceramic optical waveguide as an active media to achieve continuous wave 1.06 pm laser operation. We have obtained output laser power of 40 mW and with a laser slope efficiency in excess of 40%. Single mode and stable laser oscillation have been achieved by using the natural Fresnel reflection for optical feedback without the requirement of any kind of mirror or reflective component. 

In absence of laser mirrors, optical feedback at the both faces was only provided by the Fresnel reflection. Taking into account the refractive index of Nd YAG ceramics (no=1.8), and using Fresnel equations. 

In this context it is noted that Kildal [2] proposed the energy spectrum of the conduction electrons in non-linear optical materials under the assumptions of isotropic momentum matrix element and isotropic spin-orbit splitting, respectively, although the anisotropies of the aforementioned band parameters are the significant physical features of this compound. Besides, III-V optoelectronic compounds find extensive application in distributed feedback lasers and infrared photodetectors. In what follows, we study the photoemission in quantum confined CdGeAs2 on the basis of a newly formulated electron... 

The term laser is an acronym (light amplification by stimulated emission of radiation) that denotes a technical device operating on the basis of the stimulated emission of light. A laser emits monochromatic, spatially coherent, and strongly polarized light. The essential parts of a laser device are an active material and a resonator, i.e. an optical feedback (see Fig. 6.10). 

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