Direct hyperspectral dual-comb imaging

Even though dual-comb-based systems are employed almost routinely nowadays in an ever-increasing number of applica-tions, an efficient combination of this effective technique withan imaging arrangement, which would undoubtedly revolu-tionize hyperspectral imaging, had not yet been demonstrated. Here we present, to our knowledge, the first hyperspectral dual-comb imaging system in which interferograms are directly detected by a video camera. The system, based on a dual-comb scheme capable of consistently generating interfer-ograms at a rate of 1 Hz and below, combines fast hyperspectral imaging with unprecedented optical resolution and fully multiplex operation. Various proof-of-principle experiments demonstrating hyperspectral imaging of molecular resonances have proved that the direct hyperspectral dual-comb imaging method presented here is capable of characterizing a scene with super-fine resolution in a narrow optical span within 1 s.European Commission (ATTRACT project Grant Agreement 777222

Wavelength modulation laser heterodyne radiometry

A novel method is proposed for improving the performance of traditional laser heterodyne radiometry. The technique, which is based on the use of a wavelength modulated local oscillator laser, provides baseline-free spectra, lower limits of detection, and better precision and consistency than the conventional approach. This tool could, therefore, boost the accuracy of current terrestrial and planetary atmospheric studies

Hydrogen Sulfide Detection in the Midinfrared Using a 3D-Printed Resonant Gas Cell

A fast and reliable photoacoustic (PA) sensor for trace gas detection is reported. The sensor is based on a 3D-printed resonant cell in combination with a continuous wave mode-hop-free external cavity quantum cascade laser to rapidly acquire gas absorption data in the midinfrared range. The cell is designed so as to minimize the window PA background at a selected acoustic resonance. The goal is a resonant PA cell capable of detecting the traces of gases using wavelength modulation of the laser source and second harmonic detection. The versatility and enhancement of the limit of detection at sub-ppm levels are investigated by monitoring specific lines of hydrogen sulfide (H2S). The noise-equivalent absorption normalized to laser-beam power and detection bandwidth is 1.07 x 10-8 W cm-1 Hz-1/2 for H2S targeting the absorption line at 1247.2cm-1. These properties make the sensor suitable for various practical sensors for water quality applications.This work was supported by the Spanish Ministry of Economy and Competitiveness (grant TEC-2014-52147-R (MOSSI) and grant TEC2017-86271-R (PARAQUA)) and by the Carlos III University of Madrid (grant for the mobility of researchers)

Sub-GHz optical resolution mid-infrared hyperspectral imaging with dual-comb

High-performance hyperspectral imaging is becoming one of the most sought-after tools in the world today by providing a wide range of capabilities and applications. However, traditional systems have significant performance limitations, mainly related to the ability to resolve narrow spectral features and to detection sensitivity. With the aim of addressing these weaknesses, we present here the first hyperspectral dual-comb imaging system capable of providing sub-GHz (<0.033 cm−1) optical resolutions and fast acquisition rates in the mid-infrared region. The system has been experimentally demonstrated by analyzing methane at 2968 cm−1 with optical resolutions of down to 300 MHz (0.01 cm−1) and time resolutions well into the sub-second range.This research was supported in part by the Ministry of Science and Innovation, State Investigation Agency, through the project PID2020–116439GB-I00

Design and evaluation of a portable frequency comb-referenced laser heterodyne radiometer

In this paper, we present the design of a laser heterodyne radiometry instrument that combines, for the first time, frequency comb calibration and a remarkably high level of portability. A design that can, therefore, be more than capable of addressing the current need for accurate ground-based greenhouse gases monitoring in urban areas and other emission hot spots. Indeed, the compact, battery-powered system allows the acquisition of atmospheric spectral characterizations, at any location, without restrictions. As its most prominent feature, the system is equipped with an electro-optic frequency comb reference that provides a set of calibration ticks from which an accurate characterization of the absorption line shape can be obtained. Besides this, the spectrometer has been designed to promptly switch between traditional operation and wavelength modulation, so the performance of future inversion models may benefit greatly by this complementary data. The system has been tested in different locations in the Madrid region (Spain), where measurements have been carried out under a wide variety of conditions. Here, a set of highly representative results is presented clearly illustrating the capabilities of the developed system.This project has received funding from the EU H2020 Consumerdriven demands to reframe farming systems project under Grant Agreement 101000216, and from the Agencia Estatal de InvestigaciÓn under Grant Project TED2021-131695B-100

Sub-ppm-level ammonia detection using photoacoustic spectroscopy with an optical microphone based on a phase interferometer

A sensitive optical microphone for photoacoustic spectroscopy based on the common path topology of a fibre laser Doppler vibrometer (FLDV) using phase-generated carrier demodulation and a slim diaphragm as an acoustic wave transducer was demonstrated. A resonant gas cell was adapted to enhance gas-detection performance and simultaneously provide efficient cancellation of the window background acoustic signal. Ammonia (NH3) was selected as the target gas. The absorption line was experimentally identified using a distributed feedback laser diode emitting at 1530 nm. The linearity and sensitivity of the gas sensor were measured using wavelength modulation spectroscopy with second harmonic detection. A Teflon diaphragm was used to implement the optical microphone, along with the FLDV, showing a minimum detectable pressure of 79.5 mu Pa/Hz(1/2). The noise-equivalent absorption sensitivity for NH3 detection at the absorption line at 1531.7 nm was 1.85 x 10(-8) W cm(-1) Hz(-1/2), and the limit of detection was 785 ppbv.This research was funded by the Government of Spain, grant number TEC2017-86271-R.Publicad

High-Resolution Optical Thickness Measurement Based on Electro-Optic Dual-Optical Frequency Comb Sources

We propose an optical thickness measurement device based on electro-optic dual-optical frequency combs (dual-OFCs). Optical frequency combs (OFCs) are light sources that provide an optical signal consisting of many equidistant monochromatic tones. In this paper, we present an agile dual-OFC architecture with adjustable frequency separation of the comb modes and total frequency span, allowing high-resolution measurements of the thickness of transparent thick samples. This architecture is based on a single continuous-wave laser diode and external electro-optic devices to implement the dual-comb sensor, allowing easy control of the optical spectrum of the interrogation source (dual-OFC). As it is characteristic of dual-OFC systems, the optical transmittance function of the sample (etalon) is directly translated to the radiofrequency domain, where detection, demodulation, and processing of signals are performed. The shift in the complexity of implementation from the optical to the electronic domain yields many advantages, as acquisition and signal processing are made independently on the optical characteristics of the sample (thickness).This work was supported by the Spanish Ministry of Economy and Competitiveness under the RTC-2015-4205-4 Salicar and TEC-2014-52147-R Mossi grants

LiDAR design for road condition measurement ahead of a moving vehicle

2017 IEEE SensorsIn this paper we present the design and the first results of a prototype road condition sensor based on diffuse reflectance spectroscopy in the near infrared using semiconductor lasers. The objective of the sensor is to alert drivers or autonomous driving assistance systems of a road condition, such the presence of water or mud or ice, that will reduce the surface grip a few meters ahead the vehicle.This work was supported by the Spanish Ministry of Economy and Competitiveness under the RTC-2015-4205-4 “SALICAR” grant

Classification of skin phenotypes caused by diabetes mellitus using complex scattering parameters in the millimeter-wave frequency range

The pathological skin phenotype caused by hyperglycemia is an important indicator for the progress of diabetes mellitus. An early detection of diabetes assures an early intervention to regulate the carbohydrate metabolism. In this publication a non-invasive detection principle based on the measurement of complex scattering parameters in the millimeter-wave frequency range is presented. The measurement principle provides evidence of the applicability for the identification of different glycemic states in animal models. The method proposed here can be used to predict diabetes status in animal models and is interesting for application on humans in view of safeness of millimeter-wave radiation. Furthermore the complex scattering parameters give important information about the anatomic varieties between the analyzed skin samples of the different mice strains. In contrast to other methods, our approach is less sensitive to skin variations between animals

In-vivo, non-invasive detection of hyperglycemic states in animal models using mm-wave spectroscopy

Chronic or sustained hyperglycemia associated to diabetes mellitus leads to many medical complications, thus, it is necessary to track the evolution of patients for providing the adequate management of the disease that is required for the restoration of the carbohydrate metabolism to a normal state. In this paper, a novel monitoring approach based on mm-wave spectroscopy is comprehensively described and experimentally validated using living animal models as target. The measurement method has proved the possibility of non-invasive, in-vivo, detection of hyperglycemia associated conditions in different mouse models, making possible to clearly differentiate between several hyperglycemic states