S. Becker

Single-mode interband cascade laser sources for mid-infrared spectroscopic applications

Compared to the near infrared, many technologically and industrially relevant gas species have more than an order of magnitude higher absorption features in the mid-infrared (MIR) wavelength range. These species include for example important hydrocarbons (methane, acetylene), nitrogen oxides and sulfur oxides. Tunable laser absorption spectroscopy (TLAS) has proven to be a versatile tool for gas sensing applications with significant advantages compared to other techniques. These advantages include real time measurement, standoff detection and ruggedness of the sensor. We present interband cascade lasers (ICLs), which have evolved into important laser sources for the MIR spectral range from 3 to 7 μm. ICLs achieve high efficiency by cascading optically active zones whilst using interband transitions, so they combine common diode laser as well as quantum cascade laser based technologies. Our application grade singlemode distributed feedback devices operate continuous wave at room temperature and are offering several features especially useful for high performance TLAS applications like: side mode suppression ratio of > 30 dB, continuous tuning ranges up to 30 nm, low threshold power densities and low overall power consumption. The devices are typically integrated in a thermoelectrically cooled TO-style package, hermetically sealed using a cap with anti-reflection coated window. This low power consumption as well as the compact size and ruggedness of the fabricated laser sources makes them perfectly suited for battery powered portable solutions for in field spectroscopy applications.

Advanced Photonic Sensors Based on Interband Cascade Lasers for Real-Time Mouse Breath Analysis

A multiparameter gas sensor based on distributed feedback interband cascade lasers emitting at 4.35 μm and ultrafast electro-spun luminescence oxygen sensors has been developed for the quantification and continuous monitoring of 13CO2/12CO2 isotopic ratio changes and oxygen in exhaled mouse breath samples. Mid-infrared absorption spectra for quantitatively monitoring the enrichment of 13CO2 levels were recorded in a miniaturized dual-channel substrate-integrated hollow waveguide using balanced ratiometric detection, whereas luminescence quenching was used for synchronously detecting exhaled oxygen levels. Allan variance analysis verified a CO2 measurement precision of 1.6‰ during a 480 s integration time. Routine online monitoring of exhaled mouse breath was performed in 14 mechanically ventilated and instrumented mice and demonstrated the feasibility of online isotope-selective exhaled breath analysis within microliters of probed gas samples using the reported combined sensor platform.

Single-mode interband cascade laser multiemitter structure for two-wavelength absorption spectroscopy

Abstract. An interband cascade laser multiemitter with single-mode distributed feedback (DFB) emission at two wavelengths is presented. Continuous-wave laser operation is measured from 0°C to 40°C with threshold currents of around 25 mA and output powers of around 9 mW at 20°C. The ridge waveguide DFB structures are monolithically integrated with a spacing of 70  μm and each is provided with an individual metal DFB grating to select specific single-mode wavelengths of interest for absorption spectroscopy. The emission windows at 3.92 and 4.01  μm are targeting hydrogen sulfide and sulfur dioxide, which are of importance for industrial applications since both gases are reagents of the Claus process in sulfur recovery units, recovering elemental sulfur from gaseous hydrogen sulfide.

Novel mono mode interband cascade laser sources for challenging TLAS applications in the MIR

Tunable Laser Absorption Spectroscopy (TLAS) in the mid-infrared (MIR) wavelength region from 3 to 6 μm has proven to be a versatile tool for a variety of challenging gas sensing applications, especially for many technologically or environmentally relevant gases like e.g., methane or sulfur dioxide. In general, semiconductor lasers used for Tunable Laser Absorption Spectroscopy comprise also quantum cascade lasers (QCLs) and diode lasers, but both approaches experience problems for TLAS in the mid-infrared wavelength region. While conventional diode lasers lack the ability to cover the entire target wavelength range from 3 to 6 microns, quantum cascade lasers can reach this spectral range of interest, but they still suffer from extensive threshold power densities as well as a high overall power consumption compared to interband cascade lasers (ICLs). Interband cascade lasers are able to offer suitable application-grade device performance figures with low power consumption in the wavelength range of interest for Tunable Laser Absorption Spectroscopy applications. TLAS requires single mode emitting devices, like distributed feedback (DFB) lasers. To fabricate DFB ICLs, we use metal grating structures laterally to the laser waveguide ridge defined by e-beam lithography. Based on different epitaxial material, the current short-wavelength as well as long-wavelength records for GaSb based DFB ICLs were observed. Distributed feedback lasers with tuning ranges up to 25 nm, side mode suppression ratio> 30 dB and low power consumption below 250 mW at room temperature in continuous wave operation have been achieved. These devices and the related performance enable a wide variety of new applications, from process control to environmental monitoring or applications in medical diagnosis like breath analysis.

Cost-effective tunable laser gas-sensor module for high-volume applications, using DFB laser diodes in the NIR, and ICL in the MIR

This talk gives an insight into the development and the device performance of various tunable Laser Diodes (LD) in the near infrared (NIR) region between 760 nm and 3000 nm, and Interband Cascade Laser (ICL) based sources in the mid infrared (MIR) wavelength region between 3000 nm and 6000 nm for application in high accuracy gas sensing. Distributed Feedback (DFB) type ICL and LD devices based on a lateral metal grating structure were fabricated using an overgrowth free processing route. These devices have been realized in the entire spectral range from 760 nm to 5200 nm up to now. Total tuning ranges of up to 20 nm can be covered by these DFB devices providing typically a few mW of optical output power with low power consumption based on a low operating current and voltage. All fabricated NIR and MIR sources are targeting high performance sensor applications in fields like industrial process control or environmental monitoring. Various application examples utilizing this Tunable Laser Absorption Spectroscopy (TLAS) will be highlighted in the talk.

Interband cascade laser sources in the mid-infrared for green photonics

Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool for gas sensing applications with significant advantages compared to other techniques. These advantages include real time measurement, standoff detection and ruggedness of the sensor. Especially the Mid-Infrared (MIR) wavelength region from 3 to 6 microns is of great interest for industrial process control and the reduction of pollutants. In this contribution we present novel ICL devices developed to address the crucial air pollutant sulfur dioxide SO2 at its transition around 4 μm. In general, interband cascade lasers (ICLs) have evolved into important laser sources for the MIR spectral range. Compared to quantum cascade lasers, they offer significant advantages with respect to threshold power density as well as overall power consumption. In contrast to conventional diode lasers, ICLs are able to cover the entire MIR wavelength range of interest. For application in TLAS, single-mode devices are required. In this work application-grade distributed feedback (DFB) ICL devices for addressing SO2 at the wavelength range around 4 μm are presented. A lateral metal grating, defined by electron beam lithography, is used to achieve DFB operation and hence spectrally single-mode emission. Continuous wave laser operation with threshold power consumption below 100 mW at room temperature, side mode suppression ratio of > 30 dB and wavelength tuning range up to 28 nm are demonstrated.