Lead salt diode lasers

Quantum laser Lead-salt diode lasers 10,000 10 kHz 3-30... 

FIGURE 11.5 Variation of laser frequency and signal with current for a typical lead salt diode laser (adapted from Werle et al., 1992). 

In order to determine exact quantitative data it is necessary to obtain high resolution spectra of the dimer. Since a resolution of < 0.001 cm i is beyond the scope of FTIR spectrometers, laser spectroscopic techniques were required. This could be aciiieved in an IR study using sensitive absorption measurements by a lead salt diode laser. 

For semiconductor lasers in general, and lead-salt diode lasers in particular, linewldth calculations based even on the first order Schawlow-Townes formulation of Eq. (2) will yield numerical values that are typically several kHz to tens of kHz wide. The reasons for this are as follows. 

To begin with, the typical single mode output power of lead-salt diode lasers presently available is generally (much) less than 10 mw. Also, Qc, the "cold" cavity Q calculated for a "solitary" diode laser (the cavity of which is defined by two cleaved end facets) is generally much less than 10. In terms of the usually measured semiconductor laser parameters the full Lorentzian linewidth between half-maximum power points (FWHM) can be written as... 

Fig. 6. Emission wavelength range of various tunable lead-salt diode lasers.

C. Freed, J. W. Biellnskl, and W. Lo, "Programmable, Secondary Frequency Standard Based Infrared Synthesizer using Tunable Lead-Salt Diode Lasers," Proceedings of Tunable Diode Laser Development and Spectroscopy Applications," SPIE 438, (1983). 

A periodically updated list of papers and reports on lead-salt diode lasers and their applications is available on request from the Laser Analytics Division of Spectra-Physics, Inc., Bedford, MA 01730. 

Successful detection of various trace gases at concentration levels typically of the order of parts per billion has been achieved with mid-IR laser sources, including lead-salt diode lasers and, more recently, QCLs. 

Impurities with Lead-Salt Diode Lasers. 744... 

Detection of Molecular Gas Impurities with Lead-Salt Diode Lasers [2], [9]... 

Fig. 14.7 Spectral coverage of the visible to infrared region by different semiconductor laser materials while for junction lasers room-temperature operation is only possible up to 2-3 pm for Group III-V materials, quantum cascade lasers become a promising alternative to the cryogenic cooled Group IV-VI lead-salt diode lasers (Reprinted with permission from Werle et al. (2002). Copyright 2002 Elsevier)...

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). 

Time-resolved spectroscopy is performed using a pump-probe method in which a short-pulsed laser is used to initiate a T-jump and a mid-IR probe laser is used to monitor the transient IR absorbance in the sample. A schematic of the entire instrument is shown in Fig. 17.4. For clarity, only key components are shown. In the description that follows, only those components will be described. A continuous-wave (CW) lead-salt (PbSe) diode laser (output power <1 mW) tuned to a specific vibrational mode of the RNA molecule probes the transient absorbance of the sample. The linewidth of the probe laser is quite narrow (<0.5 cm-1) and sets the spectral resolution of the time-resolved experiments. The divergent output of the diode laser is collected and collimated by a gold coated off-axis... 

Linewldth Considerations and Lead-Salt Tunable Diode Lasers... 

It would be premature, however, to conclude that the extremely narrow (20-30 kHz) linewidths achieved with broad-area, homojunction solitary PbSi xSex tunable diode lasers can be obtained with all other lead-salt compounds and diode structures as well. Figure 6 shows some of the most frequently used lead-salt semiconductors which can provide a class of tunable lasers with emission wavelengths anywhere between about 2 1/2 um and 30 um. The figure illustrates the dependence of laser wavelengths on composition of the lead-salt compounds. The lower left portion of the figure shows PbEuSeTe which can be used to cover the 2.6 to 6.6 pm wavelength range. This is a new material recently developed at the... 

General Motors Research Laboratories (GMR). Molecular beam epitaxial (MBE) growth of Pbi xEuxSeyTei y lattice-matched to PbTe substrates has been used to fabricate double heterojunction diode lasers, including quantum well, large optical cavity (LOG) devices, the first such TDL structures reported for a lead-salt compound. These Mesa stripe... 

D. L. Partin, "Lead Salt Quantum Well Diode Lasers", Superlattices and Microstructures, 1, 131 (1985). 

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