Semiconductor-Diode Lasers

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). 

Muller R et al 1996 Time-resolved identification of single molecules in solution with a pulsed semiconductor diode laser Chem. Phys. Lett. 262 716-22... 

A semiconductor laser takes advantage of the properties of a junction between a p-type and an n-type semiconductor made from the same host material. Such an n-p combination is called a semiconductor diode. Doping concentrations are quite high and, as a result, the conduction and valence band energies of the host are shifted in the two semiconductors, as shown in Figure 9.10(a). Bands are filled up to the Fermi level with energy E. ... 

Semiconductor diodes Semiconductor industry Semiconductor lasers... 

Fig. 11. Schematic diagram of semiconductor diode laser where the junction is ca 1 ]lni. Other dimensions are <1 mm.

Fig. 12. Details of an aluminum gallium arsenide semiconductor diode laser.

Because there are two changes ia material composition near the active region, this represents a double heterojunction. Also shown ia Figure 12 is a stripe geometry that confines the current ia the direction parallel to the length of the junction. This further reduces the power threshold and makes the diffraction-limited spreading of the beam more symmetric. The stripe is often defined by implantation of protons, which reduces the electrical conductivity ia the implanted regions. Many different stmctures for semiconductor diode lasers have been developed. 

Fig. 13. Availability of semiconductor diode lasers where represents the Al Gaj As system, UIn..Gaj As Pj, and I AlInGaP. ...

The pump source in the dispersive experiment is typically a nanosecond laser the probe source can be broadband IR light from a globar or tunable IR light from a CO laser or a semiconductor diode laser. Although CO and diode lasers can produce... 

The development of semiconductor diode lasers with wavelengths shorter than those used for CD-based systems means that there is a need for dyes which can exploit these wavelengths (635-650 nm) to obtain higher-density data storage, as in DVD media. Azo metal-chelate dyes can have absorption maxima in the appropriate region, and, coupled with their excellent light resistance and durability, are possible candidates for use in this respect. However, their recording and readability characteristics need to be improved. 

See also Planar cavity surface-emitting laser (PCSEL) diodes Vertical cavity surface-emitting laser (VCSEL) diodes compound semiconductor-based, 22 179 Laser Doppler velocimetry (LDV), 11 784 Laser Doppler velocimeters, 11 675 Laser-drilled surgical needles, 24 206 Laser dye energy levels, 14 702-703 Laser fabrication techniques, titanium, 24 857... 

Figures 2.13(a) and 2.13(b) illustrate the basis of a semiconductor diode laser. The laser action is produced by electronic transitions between the conduction and the valence bands at the p-n junction of a diode. When an electric current is sent in the forward direction through a p-n semiconductor diode, the electrons and holes can recombine within the p-n junction and may emit the recombination energy as electromagnetic radiation. Above a certain threshold current, the radiation field in the junction becomes sufficiently intense to make the stimulated emission rate exceed the spontaneous processes.

For the last decade, semiconductor diode-laser sensors have been developed at Stanford University for measurements of important parameters in laboratory-and industrial-scale gaseous flowfields. For example, a mass flux sensor was developed based on rapid measurements of O2 absorption near 760 nm in supersonic flowfields [1] and a multiplexed sensor was developed for the simultaneous measurement of various pollutants representing unburned hydrocarbons (CH4, CH3CI) near 1.65 pm [2]. 

Raman analysis is performed using Raman microspectrometers in backscattering geometry. Analysis of nanodiamond requires the use of ultraviolet (UV) excitation and spectra were recorded using a Raman spectrometer with a 325-nm HeCd laser. Visible (VIS) Raman spectra were acquired using a 514-nm Ar-ion laser, a 633-nm HeNe laser, and a 785-nm semiconductor diode laser. 

Figure 7.5. (A) Schematic of semiconductor diode laser junction and (B) corresponding energy diagram. Junction region is only a few micrometers thick, and light output is quite divergent. Eg is the semiconductor bandgap.

The vibration-rotation spectra of the v, and v bands of CO C1 j have been measured (using a tunable semiconductor-diode laser), and assigned with the aid of Stark modulation spectra [2224]. The precise values of these bands were determined to be 1828.2012 and 851.0105 cm", respectively, and the equilibrium rotational constants for CO Clj were calculated as = 7950.35, Bg = 3490.22, and Cg = 2425.44 MHz cf. 

Krivan V., Barth P. and Schnurer-Patschan C. (1988) An electrothermal atomic absorption spectrometer using semiconductor diode lasers and a tungsten coil atomizer design and first applications, Anal Chem 70 3625-3632. 

Ng K. C., Ali A. H., Barber T. E. and Winefordner J. D. (1988) Multiple mode semiconductor diode laser as a spectral line source for graphite furnace atomic absorption spectroscopy, Anal Chem 62 1893-1895. 

Niemax K., Zybin A., Schnurer-Patschan C. and Groll H. (1996) Semiconductor diode lasers in atomic spectrometry, Anal Chem 68 351A-356A. 

Figure 1.14 Spectra of aspirin measured with seconds of each other using a frequency-doubled Nd YAG laser (532 nm) and a semiconductor diode laser (785 nm). Illustration courtesy of Horiba (obin-Yvon Corporation.

---