Semiconductor laser temperature tuning

In the near-infrared, Al Ga As and In Ga As P lasers, and in the far-infrared lead compound semiconductor lasers are tunable by varying temperature and operating current. Many exceUent spectroscopic studies have been performed using them. However, they do have relatively limited tuning ranges for any one device. 

Another possibility for laser wavelength tuning is based on the shift of the energy levels in the active medium by external perturbations, which can cause a corresponding spectral shift in the gain profile and, therefore, in the laser wavelength. For instance, this shift may be caused by a temperature variation, as in the aforementioned case of semiconductor lasers. 

The frequency of solid-laser lines can often be tuned by temperature variationa) s for the ruby line where a shift of 20 cm has been obtained by varying the temperature between 77 °K and 300 °K. Semiconductor lasers can be frequency tuned by applying a variable mechanical pressure to the junction in the laser diode... 

The compactness and efficiency of the semiconductor laser make it particularly attractive for systems use. Other substances used have included indium arsenide, indium phosphide, indium aniimonidc. and alloys such as gallium-arsenide-phosphide. These lasers may he tuned over several percent of their normal frequency of operation by varying the current flow through the device. The tuning results from the variations in temperature with current, which, in turn, changes the index of refraction and tile resultant resonant frequency of the cavity. 

Lasers represent a special type of light source [16], [21], [60], [61]. They are used in trace analysis by fluorescence measurement or laser-induced fluorescence (LIF) (- Laser Analytical Spectroscopy) [62] - [64], in high-resolution spectroscopy, and in polarimetry for the detection of very small amounts of materials. Lasers can be of the gas. solid, or dye type [21]. In dye lasers, solutions of dyes are pumped optially by another laser or a flash lamp and then show induced emi.s-sion in some regions of their fluorescence bands. By tuning the resonator the decoupled dye laser line can be varied to a limited extent, so that what may be termed sequential laser spectrometers can be constructed [65]. In modern semiconductor lasers, pressure and temperature can also be used to detune the emission wavelength by 20-30nm [66], [67]. 

The DLAAS devices are now commercially available from Atomica Instruments (Munich, Germany). The first system was prepared for the measurement of ultra-trace levels of A1 in the semiconductor industry. The commercial laser diode module includes the DL with a heat sink for temperature tuning, the microoptics, and the non-linear crystal for SHG. The module has the size of a HCL. Since delivery, the module has successfully worked routinely under the conditions of an industrial analytical laboratory without any repair or maintenance. The semiconductor industry in particular is interested in the measurements of light elements, such as Al, K, Ca, Na, in ultra pure water or chemicals. For example, the module designed for the detection of K provides an LOD of 0.5 pg/mL (10 pL aliquot). Similar compact and sensitive devices with electrothermal atomizers, flames or micro-plasma are currently... 

AETAIR Center develops long-wave infrared (EWIR) and terahertz-frequeney (THz) lasers operating at room temperature employing intraband lumineseenee in eolloidal semieonduetor nanocrystals, in which the optical transition frequencies can be easily tuned to the desired values by an appropriate choice of the semiconductor material and radius of the nanocrystals. 

A different type of a tunable infrared gain medium is found in the tunable diode laser. The gain is produced by carrier jumps across the band gap of a semiconductor. This band gap is temperature dependent and so is the corresponding gain wavelength. This way the coarse tuning is achieved. Further details will be explained in the subsequent chapter. 

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