In recent years, the use of laser sources in gas sensing applications has been increasing continuously. Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool in a variety of sectors including industry, health and security and modern environmental analysis. Especially the mid-infrared wavelength range is of great interest for high accuracy gas sensing applications, since many technologically and industrially relevant gas species have their strongest absorption features in the spectral region between 3 and 6 μm. These include, e. g., important hydrocarbons like methane or propane, as well as nitric oxide and formaldehyde. Interband cascade lasers (ICL) provide mono mode continuous wave (CW) operation above room temperature in this wavelength range. Application-grade complex coupled distributed feedback (DFB) laser devices based on the ICL concept are presented, using lateral metal gratings as wavelength selective elements. The fabricated devices operate at specific, technologically relevant, emission wavelengths in the spectral region from 3 to 6 μm. CW operation up to 80 °C and mono mode wavelength tuning ranges above 20 nm were achieved with low energy consumption. Application examples in industry and research are presented that demonstrate the high potential of DFB ICLs for the use in TLAS. E. g., formaldehyde gas sensor systems based on DFB ICL devices operating around 3.6 μm can provide realtime in-situ measurements with resolution limits in the low ppb range, even in dense background atmospheres. The low power consumption of ICL based devices makes them especially favorable for battery-powered or portable sensor applications.
In recent years the importance of lasers in optical gas sensing has been continuously increasing. Tunable Laser Absorption Spectroscopy (TLAS) has proven to be a versatile tool in modern environmental analysis. In the mid-infrared wavelength region between 3 and 6 µm, which is of high interest for sensing applications, Interband Cascade Lasers (ICL) can provide monomode continuous wave (CW) emission at room temperature. We present the simulation, design and manufacturing of distributed feedback (DFB) laser devices based on this concept, with focus on devices that target specific, technologically and industrially relevant, wavelengths with low energy consumption. Finally application-grade devices from 3 to 6 µm are presented. CW operation above room temperature and tuning ranges of 11 nm with Side Mode Suppression Ratios (SMSR) greater 30 dB were achieved.
Tunable Laser Absorption Spectroscopy in the mid-infrared wavelength region, especially between 3 and 6 µm, is of great interest for high performance gas sensing applications. Interband Cascade Lasers can provide monomode continuous wave (cw) emission above room temperature in this wavelength range. We present the simulation, design and manufacturing of application-grade distributed feedback laser devices based on this concept. The fabricated devices successfully target specific, technologically relevant, wavelengths in cw operation above room temperature with low energy consumption. Output powers above 5 mW, high Side Mode Suppression Ratio around 30 dB and tuning ranges of up to13 nm were achieved.
Novel monolithic widely tunable laser diodes in the 2.1μm wavelength region based on GaSb / AlGaAsSb are
presented. Using the concept of a lateral binary superimposed (BSG) grating structures and multisegment Verniertuning,
stable single-mode output is realized at discrete wavelength channels in the 2060 nm – 2140 nm region. A total
tuning above 80 nm in six channels is demonstrated. In every wavelength channel, the output wavelength can be tuned
by current and temperature. Each wavelength channel offers up to 6 nm of mode hop free tuning, making this novel
widely tunable laser highly attractive as a monolithic light source for multiple-gas sensing or liquid detection purposes.
The wavelength channels can be arbitrarily placed within the material gain allowing BSG lasers to sweep e.g. over
several gas absorption line within 80 nm.
Within a wavelength channel, the widely tunable lasers show DFB like spectral performance with average side-mode
suppression-ratios above 40 dB, output power of up to 15 mW at 25°C. Also temperature and current tuning coefficients
are comparable to those of DFB lasers.
This paper will present an overview of laser concept, performance data and applications.
The combination of high power, small linewidth and rapid tuneability is essential for many fields in high resolution spectroscopy. Furthermore these optical features are essential for laser-cooling techniques. Enhancement of high power lasers with excellent spectral and spatial quality is currently an important research subject. The requirements for a laser system applied in both fields of application are demanding: a mode-hop free tuning range of a few GHz, with a linewidth in the order of 1MHz and an output power of a few 100mW. We report a very compact external cavity diode laser system (ECDL) with an output power of up to 800mW with an almost Gaussian shaped beam quality (M2<1.2). The coupling efficiency for a single mode fibre exceeds 60%. The centre wavelength can be preadjusted within the tuning range of 20 nm. This laser operates single mode with a mode-hop free tuning range of up to 15GHz without current compensation and a side-mode-suppression better than 50dB at different wavelength between 730 and 1060nm.
To demonstrate the suitability for neutral atom cooling we used this laser as light source in the production of a BEC of over a million 87Rb atoms. In addition we approved this light source for high resolution spectroscopy, more precisely for the Cavity-Ring-Down-Spectroscopy (CRDS). Our ECDL was part of a MIR-light source which utilizes difference-frequency-generation in PPLN. At the wavelength of 3.3μm we were able to perform a high resolution absorption measurement of 50ppb Ethane. Both applications clearly demonstrate the suitability of this laser for high-precision measurements.
Since the introduction of laser-cooling techniques for neutral atoms, the enhancement of high-power lasers with excellent spectral and spatial quality has been an important research subject. We report a new principle of using high-power laserdiodes directly in an external cavity. The very compact design offers an output power of up to 1 W and an excellent beam quality (M2 < 1.2). The coupling efficiency for a single mode fiber exceeds 60%. The center wavelength can be tuned between 775 nm and 785 nm. This laser operates single mode with a mode-hop free tuning range of up to 15 GHz without current modulation and a side-mode suppression better than 55 dB. Demonstrating the suitability for neutral atom cooling we used this laser as light source in the production of a BEC of over a million 87Rb atoms.