UNIMIR - Mirsense

Power and precision

Laser spectroscopy is a technique used to measure concentration of molecules in various applications like pollution monitoring, process control or non-invasive medical monitoring. Indeed, most molecules absorb infrared light at specific wavelengths and therefore, by tuning our infrared laser at the right wavelength and shining it on a given gas, liquid or solid sample, our clients can determine the amount of molecules present in the sample with the right detection setup (using pyroelectric detectors or photoacoustics for example).

One core parameter of successful laser spectroscopy is the selected wavelength and mirSense offers its clients the unprecedented 10 to 19 microns wavelength spectrum. The production of QCL lasers in the 10-19 microns range is unique in the world as mirSense holds an exclusive license of this technology developed at the University of Montpellier, France. In this long wave wavelength region, customers can detect various molecules like OH radicals, BTEX or hydrogen cyanide (see below some examples). Furthermore at these long wavelengths, the intrapulse linewidth broadening is relatively smaller than in the mid-infrared region and therefore, pulsed operation can be more attractive for spectroscopy.

The uniMir lasers are mounted on a thermoelectric cooler (TEC) inside a sealed High Heat Load (HHL) package integrating a collimation lens and a thermistor to readout the laser chip temperature. By controlling the chip’s operating temperature through the TEC element inside the laser’s package, customers tune the emission wavelength without mode hopping while keeping a single-mode operation.

HHL-package diagram showing the built-in thermistor that monitors the laser chip temperature and the base plate that dissipates the heat generated by the laser and the TEC.

Example of emission spectra as a function of the chip temperature for a QCL emitting at the wavelength of 17.7 µm. These DFB lasers are single mode with a side mode suppression ratio larger than 25dB.

Typical output characteristics of a DFB QCL emitting at 13.5µm.

mirSense can manufacture any wavelength in the 10-19 µm range and below are examples of gases that can be measured by spectroscopy at specific wavelengths.

General datasheet presenting the 10-19 µm offer

Application family	Wavelength		Measurable species	QCL product datasheet when available
OH Hydroxyl radical spectroscopy	~18.8 µm	~531 cm-1	OH radical	UN0530Q003HNA
Fundamental science	~ 17.7 µm	~ 565 cm-1		UN0565C002HNA
Carbon emissions	~ 15 µm		CO2
Fluoro	~ 10.5 µm	~ 948 cm-1	SF6 Sulfur hexafluoride
VOC	~ 13.7 µm	~ 729 cm-1	Toluene	UN0746C005HNA
VOC	~ 14.4 µm	~ 694 cm-1	Toluene
VOC	~ 14.3 µm	~ 697 cm-1	Ethylbenzene
VOC	~ 13 µm	~ 769 cm-1	m-Xylene	UN0746C005HNA
VOC	~ 12.6 µm	~ 795 cm-1	p-Xylene	UN0746C005HNA
VOC	~ 13.5 µm	~ 741 cm-1	o-Xylene	UN0746C005HNA
Nitrogen	~ 10.7 µm	~ 930 cm-1	NH3 Ammonia
Nitrogen	~ 17.2 µm	~ 581 cm-1	Nitrous oxide N2O
Nitrogen	~ 10.6 µm	~ 941 cm-1	N2H4 Hydrazine
Nuclear	~ 11.3 µm	~ 885 cm-1	CH3i Methyl Iodide	UN0885C010HNA
Toxic	~ 11.8 µm	~ 850 cm-1	COCl₂ Phosgene
Toxic	~ 14 µm	~ 713 cm-1	HCn Hydrogen cyanide	UN0713C005HNA

Some publications with our lasers

You may read below a publication about OH radical spectroscopy with a 19µm QCL wavelength from mirSense:

Nicholas M. Kuenning, Nicolas Q. Minesi, Brett A. Honaker, R. Mitchell Spearrin,
THz rotational absorption spectroscopy of the hydroxyl radical at high temperatures using a quantum-cascade laser,
Proceedings of the Combustion Institute,
Volume 40, Issues 1–4,
2024,
105480,
ISSN 1540-7489,
https://doi.org/10.1016/j.proci.2024.105480.
(https://www.sciencedirect.com/science/article/pii/S1540748924002888)
Abstract: A THz-frequency quantum-cascade laser absorption sensing method was developed for quantitative, time-resolved pure rotational spectroscopy of the hydroxyl radical in combustion environments. A systematic wavelength selection process involving consideration of line strength, temperature sensitivity, and spectral interference resulted in the down-selection of a group of rotational OH transitions near 531 cm−1 (15.9 THz). Spectrally-resolved measurements of multiple transitions were achieved using a pulsed quantum-cascade laser (QCL) at a measurement rate of 25 kHz with an integration time of approximately 5µs. A neighboring water line within the scanning range of the laser enables the water spectra to be measured and subtracted, removing the already minimal water interference near the target OH feature. The THz-range sensor was integrated on a high-enthalpy shock tube to validate the line strengths of the selected OH transitions at or near equilibrium in shock-initiated oxidation of argon-diluted ethylene and oxygen mixtures over a range at temperatures between 1500–3500 K. Quantitative species time histories were also measured during chemical non-equilibrium of ethylene and methanol oxidation to demonstrate the capability to resolve transient formation and destruction of OH during combustion. A detection limit of approximately 0.5 ppm-meter was demonstrated. To the authors’ knowledge, this work represents the first laser absorption sensing of the pure rotational spectra of OH at combustion conditions, exhibiting high potential for numerous applications.
Keywords: Hydroxyl; Shock tube kinetics; Laser absorption; THz; Rotational spectroscopy

Unimir benefits

Very tight linewidth that drives the very high sensitivity of gas sensing
CW operation (up to 17.7µm wavelength) delivering mW levels of output power at room temperature (pulsed operation only beyond 18µm wavelength)
Pulsed operation for larger tuning range is a good option because at these long wavelengths, the intrapulse linewidth broadening is relatively small
Low power consumption for integration in portable gas analysers
Very stable over time with good Allan deviation results when integrated inside a gas analyser

At the Photonics West 2021 laser show, mirSense was a finalist at the Prism Award in the category smart sensing for the uniMir quantum cascade lasers that allow new spectroscopy applications in the 10 to 17 microns wavelength spectrum like Benzene detection or OH radical measurement.