M. Tacke

The complex propagation constant of multilayer waveguides: an algorithm for a personal computer

An algorithm for the calculation of the propagation constant of integrated-optics waveguides is developed. The waveguide may consist of any number of layers with complex refractive indexes due to gain and loss. It allows the additional determination of the field distribution. Thus, all parameters necessary for heterostructure laser development can be calculated. The resulting program was run on a personal computer; numerical results are presented. >

New developments and applications of tunable IR lead salt lasers

Abstract 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.

Near‐room‐temperature operation of Pb1−xSrxSe infrared diode lasers using molecular beam epitaxy growth techniques

Double‐Heterostructure lasers have been fabricated with an active layer of PbSe sandwiched between cladding layers of Pb1−x Srx Se. They were operated up to T=290 K (17 °C) in pulsed and T=169 K in cw mode. This is the highest operational temperature in pulsed mode reported for lead salt lasers in the mid‐infrared. The emission wavelength tunes with temperature from 8.0 μm (T=20 K) to 4.4 μm (T=285 K).

MIDINFRARED LEAD SALT MULTI-QUANTUM-WELL DIODE LASERS WITH 282 K OPERATION

IV‐VI multiple‐quantum‐well lasers with seven wells made from molecular‐beam‐epitaxy grown PbSe/PbSrSe have been operated in pulsed mode up to 282 K at a wavelength of λ=4.2 μm. This is the highest midinfrared quantum well laser operation temperature observed to date.

Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers

A novel fiber optic evanescent wave spectroscopy (FEWS) system is based on a tunable diode laser (TDL) source, on a polymer‐coated AgClBr infrared transmitting fiber, and on a mercury cadmium telluride detector. This system was used for sensing low levels of chlorinated hydrocarbons in water. The detection limit was 100 μg/l (100 ppb), which is an improvement by a factor of 50 in comparison to a similar system that is based on a Fourier transform infrared spectrometer, and the measurement time was reduced by a factor of 3. The TDL‐FEWS system shows significant potential for in situ monitoring of ground water.

Infrared fiber-optical chemical sensors with reactive surface coatings

Abstract A review is presented of the activity of our research group in the area of mid-infrared (MIR) fiber-optical chemical sensing systems based on the new generation of infrared-transparent fiber materials such as chalcogenide (AsSeTe) and silver halide (AgBrAgCl). The availability of these fiber materials extends the optical window utilizable for chemical-sensor systems significantly into the MIR range (2–20 μm). The increasing number of publications on this topic during recent years attests to the modified IR-transparent fibers as chemical IR sensors for the on-line analysis of IR-active compounds in aqueous solutions (chlorinated hydrocarbons, glucose) and in the gas phase (chlorofluorohydrocarbons) as developed in our laboratory.

Infrared double‐heterostructure diode lasers made by molecular beam epitaxy of Pb1−xEuxSe

Infrared (IR) diode lasers have been made by growing heterostructures or graded structures of Pb1−xEuxSe. This IV‐VI ternary has a small lattice variation within the IR band‐gap range. Double‐heterostructure lasers with PbSe active layers were operated up to T=174 K cw and 220 K pulsed mode; they reached the highest cw operation temperature reported for this type of laser in the mid IR. Their tuning range was 7.8–5.7 μm cw. Lasers with the ternary as the active layer were operated up to the shortest wavelength of 2.88 μm at 100 K cw. At present lasers made by molecular beam epitaxy of this material cover the widest wavelength region at T>77 K around 5 μm in cw operation.

Molecular beam epitaxy of Pb1-xSrxSe for the use in IR devices

Abstract PbSrSe grown by molecular beam epitaxy (MBE) is investigated as a material for mid-infrared devices. Properties of PbSrSe films grown on BaF 2 (111) substrates are compared with those of PbEuSe films. Sr and Eu concentrations in the films have been determined spectroscopically (AAS, AES, EDX). Lattice parameters of Pb salt films, BaF 2 substrate and PbSe bulk material have been assessed by X-ray diffraction. Electronic properties at 300 and 77 K were investigated using Hall measurements. With increasing Sr or Eu content the bandgap energy increases strongly while the lattice constant changes very little. Thus only minor strains are expected using PbSrSe as cladding material in a double heterostructure laser. Hall data favour the application of the Sr ternary alloy.

Enhancing the Sensitivity of Chemical Sensors for Chlorinated Hydrocarbons in Water by the Use of Tapered Silver Halide Fibers and Tunable Diode Lasers

Tapered silver halide fibers were used for the first time for high-sensitivity fiber evanescent wave spectroscopic (FEWS) measurements of chlorinated hydrocarbons (CHCs) in water at trace level. The sensor arrangement consisted of a tunable diode laser (TDL) source, a polymer-coated and tapered silver halide fiber, and a direct fiber/mercury cadmium telluride (MCT) detector coupling. A minimum detection limit of 50 μg L−1 was achieved by using a polyisobutylene-coated fiber with a 1:4 tapering ratio. The sensor response is in the minute range and shows reversible analyte enrichment.

Detection of Hydrocarbons in Water by MIR Evanescent- Wave Spectroscopy with Flattened Silver Halide Fibers

IR transmitting AgCl x Br1-x, fibers were used as internal reflection elements for the spectroscopic detection of hydrocarbons that are dissolved in water in an attenuated total reflection (ATR) type of setup. The fibers were partly flattened by pressing and then coated with an analyte-enriching organic polymer in order to increase the sensor sensitivity. A portable tunable diode laser spectrometer served as a spectrometric unit. The dependence of the sensitivity on coupling conditions was investigated and lead to an optimized coupling. It is shown that the sensitivity of the flattened waveguide with a thickness of 170 μm can be enhanced by a factor of 5 compared to a fiber with 900 μm diameter. Aqueous toluene solutions with concentrations in the parts-per-million range were used to characterize the sensor system that showed a linear response with regard to analyte concentration. The noise equivalent concentration (NEC) was on the order of 1 ppm.