arXiv subjects

Jan C. Petersen

Publications and source records attributed to Jan C. Petersen.

12 recordsLinked to original sources

arXiv2020

Continuous-wave coherent Raman spectroscopy for improving the accuracy of Raman shifts

Raman spectroscopy is an appealing technique that probes molecular vibrations in a wide variety of materials with virtually no sample preparation. However, accurate and reliable Raman measurements are still a challenge and require more robust and practical calibration methods. We demonstrate the implementation of a simple low-cost continuous-wave stimulated Raman spectroscopy scheme for accurate and high-resolution spectroscopy. We perform shot noise limited continuous-wave stimulated Raman scattering (cwSRS) as well as continuous-wave coherent anti-Stokes Raman scattering (cwCARS) on polystyrene samples. Our method enables accurate determination of Raman shifts with an uncertainty below 0.1 cm$^{-1}$. The setup is used for the characterization of reference materials required for the calibration of Raman spectrometers. Compared with existing standards, we provide an order of magnitude improvement of the uncertainty of Raman energy shifts in a polystyrene reference material.

physics.optics↗

arXiv2019

Simple and robust speckle detection method for fire and heat detection in harsh environments

Standard laser based fire detection systems are often based on measuring variation of optical signal amplitude. However, mechanical noise interference and loss from dust and steam can obscure the detection signal, resulting in faulty results or inability to detect a potential fire. The presented fire detection technology will allow the detection of fire in harsh and dusty areas, which are prone to fires, where current systems show limited performance or are unable to operate. It is not the amount of light nor its wavelength that is used for detecting fire, but how the refractive index randomly fluctuates due to the heat convection from the fire. In practical terms this means that light obstruction from ambient dust particles will not be a problem as long as a small fraction of the light is detected and that fires without visible flames can still be detected. The standalone laser system consists of a Linux-based Red Pitaya system, a cheap 650 nm laser diode, and a PIN photo-detector. Laser light propagates through the monitored area and reflects off a retroreflector generating a speckle pattern. Every 3 seconds time traces and frequency noise spectra are measured and 8 descriptors are deduced to identify a potential fire. Both laboratory and factory acceptance tests have been performed with success.

physics.app-ph↗

arXiv2018

Versatile photoacoustic spectrometer based on a mid-infrared pulsed optical parametric oscillator

We demonstrate the usefulness of a nanosecond pulsed single-mode mid-infrared (MIR) optical parametric oscillator (OPO) for Photoacoustic (PA) spectroscopic measurements. The maximum wavelength ranges for the signal and idler are 1.4 um to 1.7 um and 2.8 um to 4.6 um, respectively, and with a MIR output power of up to 500 mW. Making the OPO useful for different spectroscopic PA trace-gas measurements targeting the major market opportunity of environmental monitoring and breath gas analysis. We perform spectroscopic measurements of methane (CH4) nitrogen dioxide (NO2) and ammonia (NH3) in the 2.8 um to 3.7 um wavelength region. The measurements were conducted with a constant flow rate of 300 ml/min, thus demonstrating the suitability of the gas sensor for real time trace gas measurements. The acquired spectra are compared with data from the Hitran database and good agreement is found. Demonstrating a resolution bandwidth of 1.5 1/cm. An Allan deviation analysis shows that the detection limit for methane at optimum integration time for the PA sensor is 8 ppbV (nmol/mol) at 105 seconds of integration time.

physics.app-ph↗

arXiv2018

Designing and experimental verification of a photoacoustic flow sensor using computational fluid dynamics

A photoacoustic (PA) sensor for fast and real-time gas sensing is demonstrated. The PA sensor is a standalone system controlled by a Field-Programmable Gate Array (FPGA). The PA cell has been designed for flow noise immunity using computational fluid dynamics (CFD) analysis. The aim of the CFD analysis was to investigate and minimize the influence of the gas distribution and the flow noise on the PA signal. PA measurements were conducted at different flow rates by exciting molecular C-H stretch vibrational bands of hexane (C$_6$H$_{14}$) and decane (C$_{10}$H$_{22}$) molecules in clean air at 2950 cm$^{-1}$ (3.38 $μ$m) with a custom made mid-infrared interband cascade laser (ICL). We observe a (1$σ$, standard deviation) sensitivity of 0.4 $\pm0.1$ ppb (nmol/mol) for hexane in clean air at flow rates up to 1.7 L/min, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 2.5$\times 10^{-9}$ W cm$^{-1}$ Hz$^{-1/2}$, demonstrating high sensitivity and fast real-time gas analysis. An Allan deviation analysis for decane shows that the detection limit at optimum integration time is 0.25 ppbV (nmol/mol).

physics.ins-det↗

arXiv2017

Photoacoustic spectroscopy of NO$_2$ using a mid-infrared pulsed optical parametric oscillator as light source

A photoacoustic (PA) sensor for spectroscopic measurements of NO$_2$-N$_2$ at ambient pressure and temperature is demonstrated. The PA sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared (MIR) optical parametric oscillator (OPO). Spectroscopic measurements of NO$_2$-N$_2$ in the 3.25 $μ$m to 3.55 $μ$m wavelength region with a resolution bandwidth of 5 cm$^{-1}$ and with a single shot detection limit of 1.6 ppmV ($μ$mol/mol) is demonstrated. The measurements were conducted with a constant flow rate of 300 ml/min, thus demonstrating the suitability of the gas sensor for real time trace gas measurements. The acquired spectra is compared with data from the Hitran database and good agreement is found. An Allan deviation analysis shows that the detection limit at optimum integration time for the PAS sensor is 14 ppbV (nmol/mol) at 170 seconds of integration time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 3.3$\times 10^{-7}$ W cm$^{-1}$ Hz$^{-1/2}$.

physics.app-ph↗

arXiv2017

Quartz-enhanced photoacoustic spectroscopy as a platform for non-invasive trace gas analyser targeting breath analysis

An innovative and novel quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor for highly sensitive and selective breath gas analysis is introduced. The QEPAS sensor consists of two acoustically coupled micro-resonators (mR) with an off-axis 20 kHz quartz tuning fork (QTF). The complete acoustically coupled mR system is optimized based on finite element simulations and experimentally verified. Due to the very low fabrication costs the QEPAS sensor presents a clear breakthrough in the field of photoacoustic spectroscopy by introducing novel disposable gas chambers in order to avoid cleaning after each test. The QEPAS sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared optical parametric oscillator (MIR OPO). Spectroscopic measurements of methane and methanol in the 3.1 $μ$m to 3.7 $μ$m wavelength region is conducted. Demonstrating a resolution bandwidth of 1 cm$^{-1}$. An Allan deviation analysis shows that the detection limit at optimum integration time for the QEPAS sensor is 32 ppbv@190s for methane and that the background noise is solely due to the thermal noise of the QTF. Spectra of both individual molecules as well as mixtures of molecules were measured and analyzed. The molecules are representative of exhaled breath gasses that are bio-markers for medical diagnostics.

physics.ins-det↗

arXiv2017

Compact and versatile laser system for polarization-sensitive stimulated Raman spectroscopy

We demonstrate a compact and versatile laser system for stimulated Raman spectroscopy (SRS). The system is based on a tunable continuous wave (CW) probe laser combined with a home-built semi-monolithic nanosecond pulsed pump Nd:YVO4 laser at 1064 nm. The CW operation of the probe laser offers narrow linewidth, low noise and the advantage that temporal synchronization with the pump is not required. The laser system enables polarization-sensitive stimulated Raman spectroscopy (PS-SRS) with fast high resolution measurement of the depolarization ratio by simultaneous detection of Raman scattered light in orthogonal polarizations, thus providing information about the symmetry of the Raman-active vibrational modes. Measurements of the depolarization ratios of the carbon-hydrogen (CH) stretching modes in two different polymer samples in the spectral range of 2825-3025 cm-1 were performed. Raman spectra are obtained at a sweep rate of 20 nm/s (84 cm-1/s) with a resolution of 0.65 cm-1. A normalization method is introduced for the direct comparison of the simultaneously acquired orthogonal polarized Raman spectra.

physics.chem-ph↗

arXiv2016

Photo-acoustic sensor for detection of oil contamination in compressed air systems

We demonstrate an online (in-situ) sensor for continuous detection of oil contamination in compressed air systems complying with the ISO-8573 standard. The sensor is based on the photo-acoustic (PA) effect. The online and real-time PA sensor system has the potential to benefit a wide range of users that require high purity compressed air. Among these are hospitals, pharmaceutical industries, electronics manufacturers, and clean room facilities. The sensor was tested for sensitivity, repeatability, robustness to molecular cross-interference, and stability of calibration. Explicit measurements of hexane (C${_6}$H$_{14}$) and decane (C${_{10}}$H$_{22}$) vapors via excitation of molecular C-H vibrations at approx. 2950 cm$^{-1}$ (3.38 $μ$m) were conducted with a custom made interband cascade laser (ICL). For the decane measurements a (1 $σ$) standard deviation (STD) of 0.3 ppb was demonstrated, which corresponds to a normalized noise equivalent absorption (NNEA) coefficient for the prototype PA sensor of 2.8$\times 10^{-9}$ W cm$^{-1}$ Hz$^{1/2}$.

physics.ins-det↗

arXiv2016

Off-axis QEPAS using a pulsed nanosecond Mid-Infrared Optical Parametric Oscillator

A trace gas sensor, based on quartz-enhanced photoacoustic spectroscopy (QEPAS), consisting of two acoustically coupled micro-resonators (mR) with an off-axis 20 kHz quartz tuning fork (QTF) is demonstrated. The complete acoustically coupled mR system is optimized based on finite element simulations and experimentally verified. The QEPAS sensor is pumped resonantly by a nanosecond pulsed single-mode mid-infrared optical parametric oscillator (MIR OPO). The sensor is used for spectroscopic measurements on methane in the 3.1 um to 3.5 um wavelength region with a resolution bandwidth of 1 cm^-1 and a detection limit of 0.8 ppm. An Allan deviation analysis shows that the detection limit at optimum integration time for the QEPAS sensor is 32 ppbv@190s and that the background noise is solely due to the thermal noise of the QTF.

physics.ins-det↗

arXiv2015

Differential high-resolution stimulated CW Raman spectroscopy of hydrogen in a hollow-core fiber

We demonstrate sensitive high-resolution stimulated Raman measurements of hydrogen using a hollow-core photonic crystal fiber (HC-PCF). The Raman transition is pumped by a narrow linewidth (<50 kHz) 1064 nm continuous-wave (CW) fiber laser. The probe light is produced by a homebuilt CW optical parametric oscillator (OPO), tunable from around 800 nm to 1300 nm (linewidth ~ 5 MHz). These narrow linewidth lasers allow for an excellent spectral resolution of approximately 10^-4 cm^(-1). The setup employs a differential measurement technique for noise rejection in the probe beam, which also eliminates background signals from the fiber. With the high sensitivity obtained, Raman signals were observed with only a few mW of optical power in both the pump and probe beams. This demonstration allows for high resolution Raman identification of molecules and quantification of Raman signal strengths.

physics.optics↗

arXiv2014

Phase-Sensitive Noise Suppression in a Photoacoustic Sensor based on Acoustic Circular Membrane Modes

A photoacoustic (PA) sensor based on higher order acoustic modes is demonstrated. The PA sensor is designed to enhance the gas-detection performance and simultaneously suppress ambient noise sources (e.g. flow noise, electrical noise and external acoustic noise). Two microphones are used and positioned such that the PA signals are ($π$) out of phase. Ambient acoustic noise are approximately in the same phase and will be subtracted and thus improve the SNR. In addition, by placing the gas in- and outlets so that the gas flows through the node of the first higher order membrane mode the coupling of flow noise is approximately 20 dB lower compared with flow through the fundamental mode at 5 L/min. The noise reduction and thus the increase in sensitivity is demonstrated by measuring vibrational lines of methanol and methane using a broadband interband cascade laser emitting radiation at 3.38 $μ$m. A signal-to-noise improvement of 20 (26 dB) using higher order modes are demonstrated compared with the fundamental mode. The maximum normalized noise equivalent absorption coefficient is 1.1 $\times 10^{-6}$ W cm$^{-1}$ Hz$^{1/2}$ for a flow of 5 L/min. It is anticipated that the noise cancelation strategy may find use in many practical industrial and environmental PA sensors, where ambient noise sources plays a crucial role for the absolute sensitive.

physics.optics↗

arXiv2014

A versatile integrating sphere based photoacoustic sensor for trace gas monitoring

A compact versatile photoacoustic (PA) sensor for trace gas detection is reported. The sensor is based on an integrating sphere as the PA absorption cell with an organ pipe tube attached to increase the sensitivity of the PA sensor. The versatility and enhancement of the sensitivity of the PA signal is investigated by monitoring specific ro-vibrational lines of CO2 in the 2 mm wavelength region and of NO2 in the 405 nm region. The measured enhancement factor of the PA signal exceeds 1200, which is due to the acoustic resonance of the tube and the absorption enhancement of the integrating sphere relatively to a non-resonant single pass cell. It is observed that the background absorption signals are highly attenuated due to the thermal conduction and diffusion effects in the polytetrafluoroethylene cell walls. This demonstrates that careful choice of cell wall materials can be highly beneficial to the sensitivity of the PA sensor. These properties makes the sensor suitable for various practical sensor applications in the ultraviolet to the near infrared wavelength region, including climate, environmental and industrial monitoring.

physics.optics↗