| Abstract [eng] |
High-performance GaSb-based Widely Swept Wavelength Laser Source for Infrared Molecular Spectroscopy Applications Semiconductor laser diodes occupy ever more expanding proportion of the worldwide market due to their outstanding attributes, such as, low energy consumption, longevity, rigidity, spectral tunability and continuous wave operation at room temperature with a capability of integration and minimization. Innovative Littman – Metcalf external cavity diode laser configuration offers a wide wavelength tunability with an exceptional spectral resolution. Single-mode regime is ensured by employing diffraction grating as an optical filter, while spectral tuning is achieved by incrementing the position of the external feedback mirror. Incorporation of micro-electro-mechanical (MEMS) mirror allows to increase frequency of wavelength range scan up to 200 Hz. Laser diode operating at short-wavelength infrared (SWIR) region could be successfully implemented in non-invasive medicine, spectroscopy or gas sensor technologies. The aim of this work is to characterize Littman – Metcalf laser system in order to optimize and control principal optical/electrical properties in low and high frequency regimes to demonstrate efficient spectroscopic device. It is established that the most effective emission source of this scheme is a gain chip based on GaSb quantum well structure with curved waveguide and anti-reflection front mirror coating. Application of the gain chip in Littman – Metcalf configuration granted wide-range wavelength tunability (222 nm) with exceptional spectral resolution (< 77 pm) and high optical power (> 15 mW) in the entire range of spectral tuning. The center of the envelope is located at 2250 nm, corresponding to SWIR domain. Emission parameters can be controlled by thermal (temperature of the holder) and electrical (injection current) measures, which enables optimization of the device operation in order to satisfy different applications. High frequency Littman – Metcalf laser system accompanied with photodiode can be employed as a spectroscopic device to measure absorption spectra of blood analytes (such as bovine serum albumin, glucose, lactate and urea) in 2100 nm – 2300 nm spectral range. It is demonstrated that the performance of the external cavity diode laser system is comparable to FTIR spectrometer, nonetheless, with highly increased single scan speed (up to three orders of magnitude). Exceptional parameters of the Littman – Metcalf laser system supports an assumption that it could be effectively implemented in noninvasive medical research in SWIR range. |
