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Lead salt photoconductors are popular IR photodetectors due to their outstanding performance-to-cost ratio, high room temperature performance (D* > 1E10) and availability of large area detectors. The lead salt photodetector history has been reviewed also recognizing several more recent research developments. The chemical bath deposition technique for production of the lead salt detectors has been outlined, followed by a review of the basics for their characterization. Spectral responses of both PbS and PbSe detectors collected in a wide temperature range and properly corrected have been presented.

Mid-infrared vertical external cavity surface emitting lasers (VECSEL) were developed for the wavelength range 4 to 5 μm. The devices are based on lead salt materials grown by MBE on BaF2 or Si substrate. The VECSELs are optically pumped with a 1.55 μm wavelength laser. They are operating up to above room temperature. An output power 6 mWp was reached at a temperature of +27°C. The VECSELs are temperature tunable and lasing is observed from ∼4.8 μm at −60°C down to ∼4.2 μm at +40°C heat sink temperature.

A simple procedure for transferring PbS and PbSe quantum dots into water is presented, along with characterization of the resulting water-soluble quantum dots. The external surface of the water-soluble quantum dots include carboxylic groups, which will allow target-specific labeling of cells. As a first example, near-infrared fluorescence imaging of human colon cancer cells is demonstrated using these water-soluble near-infrared fluorophores.

Nanocrystals or quantum dots of the IV-VI semiconductors PbS, PbSe, and PbTe provide unique properties for investigating the effects of strong confinement on electrons and phonons. The degree of confinement of charge carriers can be many times stronger than in most II-VI and III-V semiconductors, and lead salt nanostructures may be the only materials in which the electronic energies are determined primarily by quantum confinement. This Account briefly reviews recent research on lead salt quantum dots.

We observe that the temperature coefficients of electron-hole pair energies $(dE/dT)$ in PbS and PbSe quantum dots depend strongly on the size of the quantum dot. With decreasing size the temperature coefficient of the lowest electron-hole pair energy ${\mathrm{dE}}_{g}/dT$ decreases by more than an order of magnitude from the bulk value. The weak temperature dependence found in the strong-confinement limit is expected for atomiclike levels, but has not been observed previously in a semiconductor.

A Lead salt midinfrared quantum-well (QW) laser on [110] orientation is proposed. Theoretical simulations of [110] QW edge-emitting lasers show a 70° temperature increase in continuous-wave operation compared to the conventional [100]-orientated lasers. This is because the gain on [100]-orientated QW structure is significantly increased. Among [100], [111], and [110] orientations, [110]-orientated QW structure offers the highest gain. PbSe∕PbSrSe QW structures were successfully grown on [110]-orientated BaF2 substrate by molecular-beam-epitaxy (MBE). Photoluminescence intensity of [110]-orientated samples was twice as high as that on [111]-orientated BaF2 substrates from the same MBE run.

The application of tunable diode lasers, both lead salt- and GaAs-based, for atmospheric trace gas monitoring is reviewed. The basic features of a typical monitoring system along with more specialized methods are described.

Tunable mid‐infrared vertical external cavity surface emitting lasers were developed for the wavelength range around 3.8–3.9 μm and 3.2–3.3 μm, respectively. The devices are based on lead salt materials epitaxially grown by MBE on a Si substrate. The active part consists of PbSe QW in a PbSrSe host layer. Both devices are operated around −20 °C and have output power of several 10 mW. By changing the cavity length, a single mode hop free tuning range up to 80 cm−1 is achieved.

Optical stabilization of tunable lead-salt diode lasers (TDL) in the mid-infrared is presented for the first time. By introducing an external feedback mirror both the linewidth is substantially narrowed and the frequency of the TDL is stabilized and controlled via this mirror in a frequency-offset locked scheme. We achieved narrowing of the linewidth by 1–2 orders of magnitude or better. The TDL is offset-locked to a CO gas laser by a heterodyne technique: the beatnote between the two lasers is used to control the length of the external resonator. By this scheme we gain the capability of absolute frequency measurements with sub-Doppler accuracy. The improved spectral properties of the diode laser provide a new tool for high-resolution molecular spectroscopy in the mid-infrared.

Around 1920, Case investigated the thallium sulfide photoconductor - €”one of the first photoconductors to give a response in the near IR region to approximately 1.1 I¼m. The next group of materials to be studied was the lead salts (PbS, PbSe, and PbTe), which extended the wavelength response to 7 I¼m. PbS photoconductors from natural galena found in Sardinia were originally fabricated by Kutzscher at the University of Berlin in the 1930s. However, for any practical applications it was necessary to develop a technique for producing synthetic crystals. PbS thin-film photoconductors were first produced in Germany, next in the United States at Northwestern University in 1944, and then in England at the Admiralty Research Laboratory in 1945. During World War II, the Germans produced systems that used PbS detectors to detect hot aircraft engines. Immediately after the war, communications, fire control, and search systems began to stimulate a strong development effort that has extended to the present day. After 60 years, low-cost, versatile PbS and PbSe polycrystalline thin films remain the photoconductive detectors of choice for many applications in the 1-€“3 I¼m and 3-5 I¼m spectral range. Current development with lead salts is in the FPAs configuration.

Results on applied infrared photoluminescence investigations of lead salt chalcogenides are presented. Interpretations of spectra and wafer maps are given. The results obtained may be applied to the investigation of material properties important for laser and detector fabrication. Ergebnisse angewandter Photolumineszenzuntersuchungen im mittleren Infrarot an Bleichalkogeniden werden dargestellt. Dabei werden sowohl Spektren als auch ortsaufgeloste Messungen interpretiert. Die erhaltenen Ergebnisse konnen zur Erforschung der Materialeigenschaften eingesetzt werden, die fur die Laser- und Empfangerherstellung aus Bleisalzen von Relevanz sind.

We present the first mid-infrared VECSEL (Vertical External Cavity Surface Emitting Laser) for wavelengths above 3 μm. The structure is very simple: A 2 μm thick PbTe layer is embedded between two high reflectance mirrors and used as gain medium. It is optically pumped with a 1.5 μm wavelength laser. Emission is around 5 μm wavelength and output power up to > 40 mWp at 110K.

Several groups of narrow gap semiconductors have become particularly interesting in the fields of pure science and technology. Among these are some of the mercury, cadmium and lead compounds and some of the semimagnetic semiconductors. We report on the crystal growth of these materials and on the latest developments to meet the requirements of basic research and technology.

A detailed study on microstructures in the form of pillars, rods and tubes based on IV-VI lead salt semiconductor structures grown in molecular beam epitaxy (MBE) was described. Several essential fabrication parameters that controlled the morphological aspects of those microstructures were clearly visualized. Tremendous enhancement of pulsed photoluminescence (PL) intensity was achieved from a single microrod or microtube compared to their bulk samples. The micropillar sample, having free-standing pillar diameter of 5 mum with an inter-pillar distance of 8 mum, showed a consistent temperature tunability of ~3.64 cm-1/0K of the pulsed PL emission peaks. All those novel results dictated a promising future of lead-salt based mid-infrared opto-electronics implemented mainly in the field of industrial trace gas-sensing.

A resonant-cavity enhanced detector operating in the mid-infrared at a wavelength around 3.6 micron is demonstrated. The device is based on a narrow-gap lead salt heterostructure grown by molecular beam epitaxy. Below 140 K, the photovoltage clearly shows a single narrow cavity resonance, with a relative line width of only 2 % at 80 K., Comment: 2 figures

The development of low-cost uncooled thermal LWIR FPAs is resulting in the emergence of a new generation of infrared sensors for applications where affordability is the prerequisite for volume production. Both ferroelectric detector arrays and silicon-based microbolometers are finding numerous applications from gun sights to automotive FLIRs. There would be significant interest in a similar uncooled offering in the MWIR, but to date, thermal detectors have lacked sufficient sensitivity. The existing uncooled MWIR photon detector technology, based on polycrystalline lead salts, has been relegated to single-element detectors and relatively small linear arrays due to the high dark current and the stigma of being a 50-year-old technology.

This paper will give a brief overview of the technology available at Laser Components and describe recent improvements in reliability and quality control. Results of recently demonstrated pulsed operation of lead salt lasers at and above room temperature will be presented. More traditional cryogenic laser operation promises to be straightforward in the future thanks to the recent development of a compact tunable IR laser source based on a lead salt laser combined with an innovative miniature Stirling cooler. This device will operate unattended and without any routine maintenance for prolonged periods and is suitable for a wide variety of laboratory and industrial applications.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Energy relaxation of an optically excited two-dimensional electron-hole gas has been investigated in PbSe as an example for dimensional quantization in a semiconductor with nearly symmetric valence and conduction band extrema. As compared with bulk-like reference samples the interband emission exhibits broadening and splitting into up to 5 clearly resolved lines. A systematic variation of the spectra with excitation density was observed: With increasing pump intensity the width of the total spectrum and the number of subbands increase due to both carrier heating and band filling. The emission bands are attributed to transitions between conduction and valence subbands with equal quantum number. Above a threshold well pronounced for each subband transition, the emission becomes stimulated. That indicates a potential for laser applications. >

Diode lasers made from IV–VI semiconductors emit in the MIR and are mainly used for high resolution spectroscopy with gas analysis as most important application. New developments driven by this use are described as well as potential new applications that in part do not depend on high spectral resolution.

This volume containsd a selection of papers from the third Infrared Plasma Spectroscopy (IPS) Workshop held in Greifswald, Germany in July 2008. Although not all the contributions have been written up in time for the deadline for this volume, nevertheless the 12 contributions presented here give a fair representation of the conference topics. The conference comprised four different types of contribution. Firstly, four invited lectures focussed on the prime areas of interest. Secondly, eight shorter contributed talks, grouped as closely as possible with the appropriate invited lecture. These contributed talks covered topics in both pure and applied infrared plasma spectroscopy. A feature of the two previous IPS conferences has been a contribution from commercial organisations namely those involved in manufacturing devices, detectors and spectrometers. This group of participants formed the third part of the conference programme and gave five oral presentations covering topics like QCL and detector/detection developments and novel spectrometer designs. The fourth contributing group comprised 27 poster presentations. It should be mentioned that some of the latter were poster versions of contributed talks. The conference was remarkable for the wide spread of topics covered in a relatively small meeting, consisting of 44 participants. The participants were made up of 34 scientists from within Europe and 4 from the rest of the world. It is interesting to reflect on changes that have occurred since the previous meeting just a year earlier. Two clear developments which have occurred are the emergence of Quantum Cascade Lasers (QCL) and their use in Cavity Ring Down (CRD) spectroscopy. A major shift from cw lead salt diode lasers to cw and pulsed QCL in both pure and applied projects now seems to be well under way. The topics covered in the earlier conferences focussed more on applying infrared spectroscopy to plasma monitoring and control. When choosing the topics to cover the scientific committee felt that this time it would be useful to emphasise new spectroscopic developments as well as covering applications. This might serve as a guide as to where the subject of infrared spectroscopy in combination with plasma sources might be heading in the future i.e. to emphasize pure infrared spectroscopy developments. The first invited lecture (G Guelachvili and N Picque) and the last invited lecture (F K Tittel, Y Bakhirkin, R Curl, A Kosterev, R Lewicki, D Thomasz and S So) were chosen to set the scene and realise this objective. The second (R Engeln, R Zijlmans, S Welzel, O Gabriel, J-P van Helden, J Ropcke and D Schram) and third (X Aubert, C Lazzaroni, D Marinov, O Guaitella, S Welzel, A Pipa, J Ropcke and A Rousseau) invited talks focussed on the application of the IR laser techniques with particular emphasis on the role of surfaces in plasmas and the relevance of plasma surface interactions. Surface plasma interactions did not feature strongly in the two earlier meetings and so this topic too, along with the emphasis on novel infrared spectroscopy techniques, represents a new direction for the conference. Paul B Davies and Jurgen Ropcke International Scientific Committee P B Davies, Cambridge, UK: Chair J Ropcke, Greifswald, Germany: Co-Chair R Engeln, Eindhoven, Netherlands G Hancock, Oxford, U K M Hori, Nagoya, Japan H Linnartz, Leiden, Netherlands R Martini, New York, USA J Meichsner, Greifswald, Germany A Rousseau, Paris, France Local Organizing Committee J Ropcke (INP: Chair) F Hempel (INP: Secretary) J Meichsner (IfP, University of Greifswald) N Lang (INP) L Glawe (INP) C Krcka (INP) B Lindemann (INP)

With optical pumping, a lead salt vertical-cavity surface-emitting laser has been operated at wavelengths in the 4.50-4.60 mm range at temperatures up to T=289 K. For a 60 /spl mu/m/spl times/90 /spl mu/m pump spot, a device with a PbSe active region and Pb/sub 1-x/Sr/sub x/Se/BaF/sub 2/ quarter-wave mirror stacks was realised which had an unsaturated peak output power of 38 mW at 249 K.

The dispersion of the refractive index in optical active layers of lead-salt injection lasers (PbTe, PbSo0.1Se0.9) is investigated. It is found that the dispersion of the refractive index in the frequency range of the emitted radiation depends on the injection current. A model, using the linear response relation between the optical gain and the refractive index is proposed to explain the experimental results. The theoretical and experimental values describing the influence of the optical gain on the dispersion in the frequency range of the emitted radiation are in good agreement. Die Dispersion des Brechungsindex im potisch aktiven Gebiet von Bleisalzhalbleiterinjektionslasern (PbTe, PbS0.1Se0.9). im Arbeitsregime wird experimentell untersucht. Dabei wird festgestellt, das die Dispersion im Frequenzbereich der emittierten Strahlung mit dem Injektionsstrom korrelliert. Ein Modell, basierend auf der linearen Response-Beziehung zwischen dem optischen Gewinn und dem Brechungsindex, wird vorgeschlagen, um den experimentell gefundenen Sachverhalt zu erklaren. Zwischen den theoretisch berechneten und den experimentellen Werten fur den Einflus des optischen Gewinns auf die Dispersion des Brechungsindexes im Frequenzbereich der emittierten Strahlung wird gute Ubereinstimmung erzielt.

Lead-salt diode lasers are useful for spectroscopic applications in the 2.5–30 μm wavelength range. These devices have previously required cryogenic cooling

Recently reported value of minority carrier lifetimes and time delays in lead salt diode lasers appear anomalous [A. Qadeer et al.: Appl. Phys. A33, 181–182 (1984)]. Two laser diodes, fabricated by the same technique (Hot Wall Epoxy) and of identical chemical constituents (PbSnTe and PbSnSe) failed to provide experimental evidence supporting these recently reported values, even when operated close to, but above the respective values of laser threshold current.

A rather simple method of lead salt diode laser fabrication is described. The optimization of the diffusion process forming the pn-junction is especially discussed with regards to the various carrier concentrations of the as-grown crystals. Liquid nitrogen cooled lead salt diode lasers of the described type meet all demands of a laser based air pollution monitoring device. Es wird eine verhaltnismasig einfache Methode der Bleisalzdiodenlaserherstellung erlautert. Insbesondere die Frage der Optimierung des Diffusionsprozesses, der den pn-Ubergang erzeugt, in Abhangigkeit von der Ausgangsladungstragerkonzentration der Kristalle wird diskutiert. Halbleiterinjektionslaser des beschriebenen Typs entsprechen voll allen Anforderungen, die an ein mit flussigem Stickstoff gekuhltes, mit Bleisalzalasern arbeitendes Schadstoffmesgerat gestellt werden.

The largest segment of postwar semiconductor research deals with the column-IV elements and their offspring, the III-V compounds. Just one column to the right, there is another closeknit family of nonmetals, the column-V semimetals As, Sb, and Bi, and the IV-VI semiconductor compounds. This review will focus on PbTe, SnTe, GeTe, and some of their alloys.1 Up until a few years ago, there would have been very little to say about the metal-semiconductor [M-SCI transition in these materials, since one of their distinctive properties has been the lack of extrinsic carrier freezeout. The discovery of deep-level defects and impurities in the IV-VI compounds has changed this situation completely, and has had a strong impact on many of their other basic properties. Currently, deep-level research generates about a third of all the papers published on the IV-VI family.

Newly developed double heterostructure (DH) lasers prepared by Molecular Beam Epitaxy (MBE) are currently in the process of gradually replacing the traditionally fabricated diffused homostructure lasers. PbTe-PbEuSeTe DH MBE lasers are routinely fabricated at Laser Analytics, Inc. (LAI) with different Eu concentrations. The active layers operate in the short wavelength range of 3–6.5 um. The MBE device structures are lattice matched, and due to their superior electrical and optical confinement have significantly improved device performance. Threshold currents as low as 1 mA (20 A/cm2) at 20K were measured; and the maximum CW operation temperature achieved so far is 175K, which is the highest currently known for ordinary DH devices. A similar effort using the LPE technology was made to develop lattice matched PbSe-PbSnSeTe laser devices. So far lasers operating in the spectral range of 8–20 um have been developed utilizing the LPE technique. High power 10-element laser arrays were fabricated for the first time using Pb salt materials. When operating at 2A injection current, those lasers produced up to 70 mW of power and were stable at 60 mW to better than 0.2% over a period of several minutes.

A brief review of the early development efforts in lead salt detectors is presented. Applications and methods of fabrication of contemporary devices are also discussed. State-of-the-art detectors are characterized for their chemical, structural, and photoelectronic properties. Performance characteristics as a function of operation temperature, frequency, background energy levels, etc., are described. Radiation effects are briefly discussed. A short summary of the mechanics of photoconductivity of the lead salt films is presented. Multi-element array designs and performance characteristics of typical current operational hardware are reviewed. Design and operational limitations are identified. Advanced concepts of Integrated (Hybrid and Monolithic) Detector Arrays are also reviewed.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Angular resolved photoemission spectra of PbS have been measured at T=300K and T = 20K in the energy range 18–100 eV. The purpose of this study was to understand the origin of indirect transitions previoulsy observed in the case of the lead salts. The spectra at low temperature show that indirect transitions dominate for 15

The information presented in this paper is directed to those individuals concerned with the fuel consumption benefits associated with the use of leaded gasoline and the reduction of lead emissions to the atmosphere through the use of automotive lead traas. A two-year experimental program conducted by the Canadian Combustion Research Laboratory of Energy, Mines and Resources Canada under winter and summer driving conditions has demonstrated that automotive exhaust lead traps can reduce lead emissions by an average of 80%. Trapping efficiency was not affected by ambient temperature, which varied from −20°C to 24°C, nor by city or highway driving. With effective reduction in lead emissions possible through the use of lead traps, energy savings associated with the use of lead in gasoline can be realized, even in the event that lead tailpipe emissions might be restricted by pollution considerations.