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Lasers made of lead salt compounds have proven to be best suited for coverage of the mid-infrared region from 3 to 30 pm. Nowadays doubleheterostructure (DH) lasers are the standard, using as active layers PbEuSSe for the short-wavelength region below 4 pm, PbEuTeSe or PbEuSe for the 4-8 pm range and PbSnTe or PbSnSe for wavelengths beyond 8 pm. Originally liquid phase epitaxy but now molecular beam and hot wall epitaxy techniques are most commonly used to produce a wide variety of laser structures. While Simple DH lasers with contact or mesa stripes for lateral confinement prevail in commercial devices, highly sophisticated prototypes with buried layer, corrugated distributed Bragg reflector (DBR) and distributed feedback (DFB) and single-and multi-quantumwell structures have been successfully manufactured. Gas spectroscopy has remained the main field of application where mode quality and tuning properties of the emitted radiation are most important. The dominant development goal has been the increase of the operating temperature to make the use of simple cooling equipment possible. Theoretical models for threshold current calculations have been established; however, the reliability of the results has been impaired by the fact that basic material properties of the ternary and quaternary compounds are not well known. In the course of this paper the state of the art and the development trends of lead salt lasers are described. The various fields of applications are summarised. Two examples-one dealing with car exhaust monitoring, the other with clinical isotopic ratio measurements of the exhaled breath-will be discussed in some detail

The broad time constant dispersion of states at the Si-SiO2 interface can be explained by the tunneling model introduced by F. P. Heiman and G. Warfield.1 The spectrum of time constants is caused by the exponential decay of the effective capture cross section for larger tunneling distances. A good agreement between theory and experiments was obtained for the oxide traps concentrated within about 10 Å from the interface.

Self-pulsations reproducibly achieved in newly developed lasers with two distributed feedback sections and with an additional phase tuning section are investigated. The existence of the dispersive self-Q-switching mechanism for generating the high-frequency self-pulsations is verified experimentally for the first time. This effect is clearly distinguished from other possible self-pulsation mechanisms by detecting the single-mode type of the self-pulsation and the operation of one section near the transparency current density using it as a reflector with dispersive feedback. The operating conditions for generating this self-pulsation type are analyzed. It is revealed that the required critical detuning of the Bragg wavelengths of the two DFB sections is achieved by a combination of electronic wavelength tuning and current-induced heating. The previous reproducibility problems of self-pulsations in two-section DFB lasers operated at, in principle, suited current conditions are discussed, and the essential role of an electrical phase-control section for achieving reproducible device properties is pointed out. Furthermore, it is demonstrated that phase tuning can be used for extending the self-pulsation regime and for optimizing the frequency stability of the self-pulsation. Improved performance of the devices applied as optical clocks thus can be expected

This paper reports the demonstration of quantum-noise-limited sensitivity in frequency modulation spectroscopy (FMS) with a lead-salt diode laser operating in the 4.8-microm region. Experimentally determined sensitivities of 10(-7) in a 1-Hz bandwidth have been demonstrated for detection of CO and CO(2) in a single-pass absorption cell. The high sensitivity obtained with our FMS apparatus can be attributed to the use of improved lead-salt diode lasers, a new optical fringe reduction method, and careful attention to optical processing of the diode laser beam.