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The temperature dependence of the gain in narrow-gap semiconductors is analyzed, as is that of the threshold current in PbSe/PbSnSe DH lasers. Several channels for current flow are taken into account: tunneling, recombination at the heterojunction, and leakage current across the heterojunction barrier. The calculated numbers are compared with experimental results. Conditions are found for room-temperature oscillation of PbSe/PbSnSe DH lasers.

In monocrystalline Pb1-xSnxSe samples of n-type with 0 ≤x≤0.37 the variation of the Ha l coefficient was observed in 4.2-300K temperature region. A model of two levels was proposed and their energetic position as a function of temperature was determined.

An investigation was made of the current-voltage characteristics of injection lasers with isoperiodic PbSnSeTe layers and of double-heterostructure lasers with a controlled carrier-density profile, based on lead selenide. The investigation was carried out in the temperature range 20–80 K. The methods used in the fabrication of lasers and in measurements under pulsed conditions are described. It is shown that at 20 K the tunnel component of the current becomes important. An increase in temperature increases the role of the thermal current and already at 80 K the diffusion component becomes the dominant one. The tunnel component of the threshold current at 80 K is ~0.25.

A method for measuring the line width Γ of the emission spectrum of a TEA CO2 laser is described and the results of such measurements are given. The experimental value Γ = 0.013 ± 0.002 cm − 1 is compared with the results of a simple modeling calculation. A good agreement is obtained between the measured and calculated results.

Semiconductor single-quantum-well double-heterostructure lasers with a Pb0.95Sn0.05Se active region from Lz=400 to 2000 AA were fabricated by hot wall molecular epitaxy. For Lz 1000 AA the laser emission corresponds to the energy gap of the material in the active region. The lowest threshold current (230 A cm-3 at 77 K) and the highest operating temperature (218 K) were obtained for the laser with Lz=2000 AA.

The high resolution spectra of the 1 - 2 and 2 - 3 transitions between excited vibrational levels of SF 6 molecules cooled to T equals 30 K in supersonic jets have been experimentally investigated by the double resonance method. A tunable high pressure CO 2 laser was used to excite molecules and the excited transitions were probed with a tunable diode laser. A computer simulation of the experimental spectra has been made. The agreement of the experimental and calculated spectra was attained with an accuracy of 10 -3 cm -1 , while the values of anharmonicity constants for the (nu) 3 mode of the SF 6 molecule were refined. The matrix elements of the dipole moment of the excited transitions and the wide range spectra of 1 - 2, 2 - 3, 3 - 4 transitions in SF 6 were also calculated.

The current status of the lead salt diode lasers developed at Lebedev Physical Institute is described. Diffused lasers, LPE lattice-matched PbSnSeTe lasers, PbSSe diode lasers with controlled carrier concentration, and PbS/PbSSes/PbSnSe heterostructure lasers with a quantum-well active region are discussed. The lasers have improved performance due to their superior electrical and optical confinement.

Operating parameters and structures of typical diode lasers based on the ternary lead‐salt crystal systems PbSnSe, PbSSe and PbCdSe are presented. We discuss the characteristics of traditional diffusion laser structures and some improved structures with controlled profiles of carrier concentration and SC SQW heterostructures prepared by hot wall molecular epitaxy.

Long delays of stimulated emission from homojunction lead chalcogenide lasers are shown to be due to the appearance of a thermoelastic waveguide because of inhomogeneous heat release, low thermal diffusivity, and high strain sensitivity.

The dynamics of excitation by CO2 laser pulses of SF6 molecules from individual rotational sublevels J″ of the ground vibrational state have been investigated in a pulsed molecular jet under essentially collisionless conditions. At different energy fluences of exciting laser pulse Φ = 10−5 + 10−1 J/cm2, the dependences of the fraction fJ of excited molecules on the rotational quantum number J″ have been obtained, when SF6 molecules were excited on the 10P(16) CO2 laser line, as well as on the 10P(18) and 10P(14) lines at Φ = 0.1 J/cm2. Comparison of experimental results with theoretical predictions18–20 shows rather strong disagreement between theory and experiments both in the population of the υ3 = 1 state and in the role of multiphoton transitions. It is shown that the narrowing of the exciting laser pulse spectrum (the 10P(16) line, Φ ≲ 10−2 J/cm2) results in drastic decrease of the fraction of excited molecules from the (υ3 = 0, J″ = 4) state which is most resonant with laser radiation.

A laser spectrometer for the investigation of a nonequilibrium molecular plasma was constructed. Diode lasers with a record width of a continuous frequency tuning range (10 cm−1 ) were used in this spectrometer. The spectrometer response time (10 nsec) made it possible to use liquid nitrogen to cool the diode lasers so that the resolution was at least 10−3 cm−1 when the tuning rate was ~105 cm−1/sec. An investigation was made of the distribution of the vibrational and rotational energies between the internal degrees of freedom of the CO2 molecules and the gas temperature in a glow discharge was determined.

The Zeeman effect in the infrared absorption spectrum of a molecule without an electronic magnetic moment was observed using a linear spectroscopic technique with a tunable diode laser. In the magnetic field B = 500 kG weak splittings of the asR(4, 1) and asR(4, 0) lines in the v 2 -band of NH 3 were recorded. The values of the Zeeman splittings in these cases were −1×10 -2 cm -1 . The picture of the Zeeman splittings observed is shown to be connected with the difference between the g -factors for the excited (υ 2 = 1) and the ground (υ 2 = 0) vibrational states of the NH 3 molecule. This difference is about (-10)-(15)% of the g -factor for the lower vibrational level of the transition.

An intracavity spectroscopy method makes use of pulsed PbSnSe lasers with external resonators. The sensitivity (signal amplitude) is increased by a factor exceeding 102. A simple theoretical model is proposed for the description of the behavior of a tunable diode laser with an external resonator when frequency-selective losses are introduced into the resonator.

Photoconductivity and photoluminescence measurements are performed on PbSe films obtained by chemical “anorganic” (CAD) and “organic” (COD) depositions. A large “blue shift” is observed in the photoconductivity and photoluminescence spectra of the “as-grown” PbSe films, as compared with PbSe single crystal. The spectra are shifted towards low energies as a consequence of the thermal annealing process which increases the size of the crystallites. The shift can be explained by the “quantum size” effect. Photoleitungs- und Photolumineszenzmessungen werden an PbSe-Schichten durchgefuhrt, die mittels chemischer “anorganischer” (CAD)- und „organischer” (COD)-Abscheidung prapariert werden. Eine grose „ Blauverschiebung” in den Photoleitungs- und Photolumineszenzspektren der „as-grown”-PbSe-Schichten im Vergleich zu PbSe-Einkristallen wird beobachtet. Die Spektren werden in Richtung niedriger Energie als Folge des Temperungsprozesses, der die Kristallitgrose vergrosert, verschoben. Die Verschiebung last sich mit dem „Quantengroseneffekt” erklaren.

An analysis is made of the factors which influence the threshold current in PbSe/Pb1–xSnxSe injection heterolasers. These factors include the waveguide structure, electron confinement, inhomogeneity of the distribution of the gain across the thickness, nonradiative recombination at the heterojunctions and in the bulk, and temperature. The conditions are identified under which anomalies can be expected in the temperature dependence of the threshold current because of the influence of free carriers on the refractive index. The results agree with the experimental values of the threshold current density for a surface recombination velocity of ~2×105 cm/sec and an internal quantum efficiency of ≤0.1.

The absorption spectra of 14NH3 and 15NH3 molecules from 930 cm-1 to 1220 cm-1 have been obtained with CW and pulsed Pb1–xSnxSe diode lasers. The laser emission frequency has been tuned by varying crystal composition, diode temperature, hydrostatic pressure, or injection current. The registration of the absorption spectra with CW PbSe laser continuously tuned by varying hydrostatic pressure has been accomplished. The possibility of gas isotope abundancies measurements by diode lasers is considered.

An investigation of time dependences of the spectral and spatial distributions of the radiation emitted by pulsed homojunction wide-contact PbS1–xSex lasers revealed excitation of autowaves (self-oscillatory waves) of the free carrier density at two similar frequencies (≲ 107 Hz). These autowaves resulted in simultaneous emission of laser radiation of two types, associated with modulation of the refractive index and of the optical gain. The width of the channels was governed by the thickness of the laser diode wafer, but was independent of the resonator width. The transverse (along with p-n junction plane) intermode spacing was governed by the amplitude and spatial period (channel width) of the autowaves. A study was made of the influence of the conditions of operation ofthe laser diodes on the autowave parameters. A strong scatter of the threshold current density in a batch of 30 injection lasers with a constant resonator length, formed freshly by four-sided cleaving from a single wafer, was attributed to changes in lateral optical confinement as a result of a change in the resonator width, which was a consequence of interference between the autowaves in the resonator induced by the lateral faces of the crystal.

A study was made of the use of middle-infrared pulsed laser diodes in investigations of the width and profile of absorption lines of molecular gases. Broadening of the absorption lines of CF2Cl2 and SF6 located in the region of 930 cm-1 was studied by correlation processing of the laser diode spectra. The coefficient representing the broadening of the CF2Cl2 lines in air depended on the buffer gas pressure and it increased from 5.7 to 12.9 MHz/Torr when this pressure was increased from 0 to 100 Torr. The broadening coefficient of the 32SF6 lines by helium was independent of the He pressure in the range 5-100 Torr and amounted to 6 MHz/Torr. The self-broadening coefficients of NH3 and CF2Cl2 were found to be 28.5 and 31.2 MHz/Torr.

The effect of superequilibrium populations in the excited states of CO2 degenerate vibrational modes under vibrational-translational non-equilibrium is investigated.

A diode laser was used in a high-resolution study of the ..nu../sub 2/+..nu../sub 4/ band absorption spectrum of the CF/sub 4/ gas. Vibrational--rotational spectra of the pumping and lasing transitions in a CF/sub 4/ laser were analyzed theoretically and its tuning characteristics were determined.

A prototype device was made for measuring the concentration of carbon monoxide in the atmosphere with the aid of pulsed injection lasers. It is suitable for operation under urban and field conditions, and has a sensitivity of 0.01 ppm. A description is given of the characteristics of the device and of the results of using it continuously for long periods.

An investigation was made of the photoluminescence emitted from epitaxial films of Pb1–xSnxSe1–yTey solid solutions (0 ≤ x 0.47, 0 ≤ y 0.65), grown by the method of liquid epitaxy on n-type PbSe substrates. Next, n-Pb1–xSnxSe1–yTey/n-PbSe heterostructures, with the Pb1–xSnxSe1–yTey active layer (0.015 ≤ x ≤ 0.092, 0.0006 ≤ y ≤ 0.026), were matched in respect of the lattice constant to the substrate (Δa/a =10−1–10−3%) and used as optically excited heterolasers. The spectral and threshold characteristics were determined as a function of the thickness of the active layer d, temperature, and resonator length. Variation of the composition of the active layer altered the emission wavelength within the range 8–12.5 μ at 77°K. Electron and optical confinement effects were observed when the thickness d was reduced. For the optimal thickness dopt≈/cm2 at 77°K. The loss factor (5.5 cm−1), gain (0.11 cm/W), and carrier density (2×1017 cm−3) in the active layer were determined.

An analysis is made of the possibility of using multicomponent solutions of IV-VI compounds in laser heterostructures free of lattice mismatch and associated defects and stresses. Characteristics of a PbSe--PbSnTeSe at lambda=10 ..mu.., are estimated. The relative jump in the refractive index needed for optical confinement is estimated to be 8%.

High-resolution spectra of the ν3 band of 192OsO4 gas were obtained using diode lasers. Eighty seven of the observed absorption lines were identified. The values of four scalar and two tensor spectroscopic constants were determined more accurately and two new constants, a scalar and a tensor, were also obtained. This set of constants can be used to calculate the spectrum of 192OsO4 up to J = 50 with an error not exceeding 10−3 cm−1.

An investigation was made of the characteristics of lasing of semiconductor (lead chalcogenide) active elements pumped longitudinally by an electron beam. The dependences of the threshold current and of the lasing efficiency on the temperature of an active element and on the electron energy were determined.

The first picosecond optical parametric oscillator based on an LiNbO3 crystal was built. It amplified tunable (near 4 μ) radiation from a semiconductor injection laser.

Stimulated emission from an external-cavity diode laser was obtained for the first time in the region of the 10 μ wavelength and high-resolution spectra were recorded under intracavity absorption conditions.

A study was made of the influence of hydrostatic pressures up to 1.8 kbar on the emission spectra of a cw PbSe injection laser at temperatures of 4.2 and 20.3 °K. The quasicontinuous tuning range was 8.2–9.2 μ (1090–1220 cm−1). The measured rates of continuous change of the mode frequency with the current and pressure reached +0.01±0.003 cm−1/mA and -0.026±0.001 cm−1/bar. The continuous pressure-tuning range was ~1.7 cm−1. At 20.3 °K the laser emitted a single mode of about 25 μW power. The pressure-tunable PbSe laser was used in the determination of the transmission spectra of Ge standards with a resolution of 10−2 cm−1.

An investigation was made of fluctuations of the output frequency of a pulsed diode laser emitting at ~ 10μ. An analysis of signals transmitted by a Fabry–Perot interferometer made it possible to determine the frequency dispersion Δνl ≈ 2.5 MHz for a normal distribution law and also the correlation time of frequency fluctuations, which was 0.2 μsec.

Academician B. M. Vul, a renowned physicist in the field of dielectrics, ferroelectrics and semiconductors, died on April 1985, at the age of 81. Born in the Ukraine in 1903, he graduated from the Electrotechnical Department of Kiev Polytechnical Institute in 1928 and in 1930-1932 did his post-graduate training under the great physicist A. F. Ioffe. Since 1934 and to his last days B. M. Vul headed a laboratory in Lebede Physical Institute of the USSR Academy of Sciences. It was there that he did his Ph.D. studies on electric breakdown of gases and solid dielectrics that were to win him wide recognition.