CC BY
8DOI 10.24412/cl-37136-2023-1-22-24
TUNABLE INFRARED LASERS FOR BIOMEDICAL AND ENVIRONMENTAL APPLICATIONS
IGOR GOLYAK1, IGOR FUFURIN1, ANDREY MOROZOV1, PAVEL DEMKIN1, DMITRIY
ANFIMOV1 AND DMITRY NAZAROV2
department of physics, Bauman Moscow State Technical University, Russia 2Science and Education Center for Photonics and IR-Technology, Bauman Moscow State Technical
University, Russia
ABSTRACT
This paper discusses the development of an infrared quantum cascade laser emitting in the range from 9.6 to 12.5 ^m. The laser is made according to a circuit with an external cavity (Littrow scheme). It is shown that the selected laser design, its energy characteristics (peak pulse power 150 mW and 8 average radiation power mW), wide tuning range (from 9.6 to 12.5 ^m), tuning step 2 cm-1, linewidth of 2 cm-1, which allows the developed device to be used in a wide range of applications in the field of spectroscopy. INTRODUCTION
The analysis of chemical compounds in a solid or liquid state is one of the most important tasks, which has not only fundamental but also applied significance. At the same time, analysis methods are largely determined by the final goal of the study, the conditions of the experiment and the time allotted for it. At the moment, there are many common methods for solving problems of identifying liquid and solid substances. The most common approach is Raman spectroscopy [1, 2]. Due to the high selectivity of Raman spectra, as well as the ability to study substances even through transparent packaging, this method has become widespread.
Methods for identifying powder samples without prior sample preparation include diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The sample is placed in a special cup, then the IR radiation incident on the sample is reflected to varying degrees through the sample. Diffuse reflectance is collected on a parabolic mirror and enters a photodetector. DRIFTS is convenient to use in laboratory settings
[3].
Another classical spectral method used in the analysis of chemical compounds is absorption spectroscopy. This method has become especially widespread for the analysis of substances in the gas phase, in particular for the identification of vapors in an open atmosphere using the passive method of FTIR spectroscopy [4, 5].
Currently, significant progress has been made in the development of quantum cascade lasers (QCLs) [6]. QCLs are unipolar semiconductor lasers with the ability to tunable wavelengths over a wide spectral range. Some QCLs are capable of tuning in a range of more than 1000 cm1 and, operating in a pulsed mode, generate peak power up to 150 mW. The use of such lasers makes it possible to obtain fairly informative spectra of diffuse reflection of substances and, as a result, to successfully identify chemical compounds [7].
RESULTS
The developed quantum cascade laser (Fig. 1) generates radiation in the wavelength range 9.6-12.5 ^m with a tuning step of 2 cm-1 and an output peak power of up to 200 mW, a pulse duration of 300 ns. The laser is built according to the Littrow scheme (external cavity quantum cascade laser).
Figure 1: Quantum-cascade laser. 1 - diffraction grating; 2 - radiator; 3 - Peltier element; 4 - QC chip; 5 - aspherical collimating lens; 6 - control board for the CC chip; 7 - cooling control board.
To record the signal, a thermoelectrically cooled mercury cadmium telluride (MCT TE) photodetector is used. The system is equipped with a 24-bit analog-to-digital converter.
The developed laser has the following technical characteristics (Table 1).
Table 1. Technical characteristics of a quantum cascade laser.
Radiation range ^m 9,6-12,5
Maximum average radiation power mW 8,0
Maximum peak pulse power mW 150
Pulse duration ns 300
Time interval between radiation pulses ^s 5,7
Tuning step, no more cm-1 2
Spectral pulse width, no more cm-1 2
Beam divergence, no more mrad 5
Output beam size mm 3,5x5,0
Power consumption (220 V 50 Hz) W 50
Overall dimensions (LxWxH) mm 130x150x250
Weight kg 6
In Figure 2 shows the spectral characteristic of the output power of a quantum cascade laser.
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c 7 di s
o c Ph 6
5 4 3 2 1 0
v
V,
OOOOMKJWCOOIOIOIOICTIOIOIO
Wavenumher, cm"1
Figure 2: Dependence of output optical power on wavenumber T= 18°C, Pulse ratio 5%, 14 V. CONCLUSIONS
This work presents a prototype of a quantum cascade laser in the range from 9.6 to 12.5 ^m. The design features and technical characteristics of the laser are presented. The paper presents a diagram of an
experimental setup, namely a laser spectrometer, for research in the field of diffuse reflectance spectroscopy [8, 9] (as an alternative to Raman spectroscopy [10]) and laser absorption spectroscopy.
The developed experimental setup can be used in the chemical industry [11], pharmacology, medicine, industrial production, ensuring chemical [12] and biological safety, and inspection activities.
The work was carried out within the framework of the Priority 2030 program. REFERENCES
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