Semiconductor light sources

J. P. Dakin, D. J. Pratt, G. W. Bibby, and J. N. Ross, Distributed optical fibre Raman temperature sensor using a semiconductor light source and detector, Electron. Lett. 21, 569 (1985). 

A LED is a semiconductor light source (17). The LEDs provide numerous advantages over other light sources such as incandescent... 

SP (Vis) Based on an optoelectronic device constructed of two ordinary light emitting diodes compatible with optosensing films. This fiberless device containing chemoreceptor, semiconductor light source, and detector integrated in a miniaturized flow-through cell 20 No data 0.7-1.2 Aqueous solutions 2011 268... 

The light source for excitation of Nd YAG lasers may be a pulsed flashlamp for pulsed operation, a continuous-arc lamp for continuous operation, or a semiconductor laser diode, for either pulsed or continuous operation. The use of semiconductor laser diodes as the pump source for sohd-state lasers became common in the early 1990s. A variety of commercial diode-pumped lasers are available. One possible configuration is shown in Figure 8. The output of the diode is adjusted by composition and temperature to be near 810 nm, ie, near the peak of the neodymium absorption. The diode lasers are themselves relatively efficient and the output is absorbed better by the Nd YAG than the light from flashlamps or arc lamps. Thus diode-pumped sohd-state lasers have much higher efficiency than conventionally pumped devices. Correspondingly, there is less heat to remove. Thus diode-pumped sohd-state lasers represent a laser class that is much more compact and efficient than eadier devices. 

The compact disk player has become a very widespread consumer product for audio reproduction. The information is stored along tracks on the disk in the form of spots of varying reflectivity. The laser beam is focused on a track on the surface of the disk, which is rotated under the beam. The information is recovered by detecting the variations in the reflected light. The compact disk offers very high fideHty because there is no physical contact with the disk. This appHcation has usually employed a semiconductor laser source operating at a wavelength of around 780 nm. Tens of millions of such compact disk players are produced worldwide every year. 

For the visible and near-ultraviolet portions of the spectmm, tunable dye lasers have commonly been used as the light source, although they are being replaced in many appHcation by tunable soHd-state lasers, eg, titanium-doped sapphire. Optical parametric oscillators are also developing as useful spectroscopic sources. In the infrared, tunable laser semiconductor diodes have been employed. The tunable diode lasers which contain lead salts have been employed for remote monitoring of poUutant species. Needs for infrared spectroscopy provide an impetus for continued development of tunable infrared lasers (see Infrared technology and RAMAN spectroscopy). 

For characterization purposes of bulk or thin-film semiconductors the features at Eq and E] are the most useflil. In a number of technologically important semiconductors (e.g., Hgi j d Te, and In Gai j ) the value of. ) is so small that it is not in a convenient spectral range for Modulation Spectroscopy, due to the limitations of light sources and detectors. In such cases the peak at E can be used. The features at Eq and are not useflil since they occur too far into the near-ultraviolet and are too broad. 

A schematic representation of a PR apparatus is shown in Figure 2. In PR a pump beam (laser or other light source) chopped at frequency 2 creates photo-injected electron-hole pairs that modulate the built-in electric field of the semiconductor. The photon energy of the pump beam must be larger than the lowest energy gap of the material. A typical pump beam for measurements at or below room temperature is a 5-mW He-Ne laser. (At elevated temperatures a more powerful pump must be employed.)... 

T. Okazaki, T. Imasaka, and N. Ishibashi, Optical-fiber sensor based on the second-harmonic emission of a near-infrared semiconductor laser as light source, Anal Chim Acta 209, 327-331 (1988). 

Another major application for microresonators is in development and fabrication of novel light sources such as resonant-cavity-enhanced light-emitting diodes (LEDs), low-threshold microlasers, and colour flat-panel displays. In wavelength-sized microresonator stmctures, semiconductor material luminescence can be either suppressed or enhanced, and they also enable narrowing of the spectral linewidth of the emitted light (Haroche, 1989 Yokoyama, 1992 Yamamoto, 1993 Krauss, 1999 Vahala, 2003). 

One use of semiconductor lasers is as the light source in fibre optics. 

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