scholarly journals Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

2017 ◽  
Vol 114 (28) ◽  
pp. 7246-7249 ◽  
Author(s):  
Lian Xiong ◽  
Wenyu Bai ◽  
Feifei Chen ◽  
Xian Zhao ◽  
Fapeng Yu ◽  
...  
Keyword(s):  
Sound Speed ◽  
Photoacoustic Signal ◽  
Laser Resonator ◽  
Trace Detection ◽  
Photoacoustic Cell ◽  
Optical Source ◽  
Photoacoustic Effect ◽  
One Dimensional ◽  
Optical Grating ◽  
Detector Crystal

The amplitude of the photoacoustic effect for an optical source moving at the sound speed in a one-dimensional geometry increases linearly in time without bound in the linear acoustic regime. Here, use of this principle is described for trace detection of gases, using two frequency-shifted beams from a CO2 laser directed at an angle to each other to give optical fringes that move at the sound speed in a cavity with a longitudinal resonance. The photoacoustic signal is detected with a high-Q, piezoelectric crystal with a resonance on the order of 443 kHz. The photoacoustic cell has a design analogous to a hemispherical laser resonator and can be adjusted to have a longitudinal resonance to match that of the detector crystal. The grating frequency, the length of the resonator, and the crystal must all have matched frequencies; thus, three resonances are used to advantage to produce sensitivity that extends to the parts-per-quadrillion level.

Trace gas detection based on photoacoustic spectroscopy in 3-D printed gas cell

2020 ◽  
Vol 28 (4) ◽  
pp. 236-242
Author(s):  
Shenlong Zha ◽  
Hongliang Ma ◽  
Changli Zha ◽  
Xueyuan Cai ◽  
Yuanyuan Li ◽  
...  
Keyword(s):  
Photoacoustic Spectroscopy ◽  
Near Infrared ◽  
Acoustic Pressure ◽  
Resonant Cavity ◽  
Photoacoustic Signal ◽  
Trace Gas ◽  
Integration Time ◽  
Photoacoustic Cell ◽  
Normal Atmospheric Pressure ◽  
Micro Resonator

A novel photoacoustic spectroscopy gas sensor based on a micro-resonator has been developed. The photoacoustic cell was designed and fabricated using 3-D printing and the photoacoustic cell volume was compressed significantly. This design greatly reduces the time of manufacturing the micro-resonator and the weight was lighter compared to traditional cells. Furthermore, the acoustic pressure distribution in the 3-D printed photoacoustic cell was analyzed by COMSOL Multiphysics software, which indicated that the strongest acoustic pressure occurred in the middle of the resonant cavity. The performance of the sensor was evaluated by detection of CH4 at normal atmospheric pressure used a near infrared distributed feedback laser emitted at 1653 nm. The characteristic of the photoacoustic signal under different pressures was also investigated. An Allan variance shows that the 3-D printed photoacoustic spectroscopy sensor has the detection limit of 1.44 ppmv (3σ) for CH4 detection at about 200 s integration time.

On transforms reducing one-dimensional systems of shallow-water to the wave equation with sound speed c 2 = x

2013 ◽  
Vol 93 (5-6) ◽  
pp. 704-714 ◽  
Author(s):  
S. Yu. Dobrokhotov ◽  
S. B. Medvedev ◽  
D. S. Minenkov
Keyword(s):  
Wave Equation ◽  
Shallow Water ◽  
Sound Speed ◽  
One Dimensional

Comparison of the Effects of Density and Sound Speed Variation in the Propagation of Planar Transient Waves

1992 ◽  
Vol 114 (3) ◽  
pp. 409-414
Author(s):  
J. H. Ginsberg
Keyword(s):  
Differential Equations ◽  
Material Properties ◽  
Sound Speed ◽  
Heterogeneous Media ◽  
Numerical Procedure ◽  
Mean Value ◽  
The Other ◽  
Transient Waves ◽  
One Dimensional ◽  
Spatial Grid

When expressed in the form of characteristic differential equations, the laws governing propagation of linear one-dimensional waves through heterogeneous media show that the only properties of significance are the sound speed c and the acoustic impedance ρc, either of which may vary spatially. The former occurs in the differential equations governing the (curved) characteristics, while the latter appears in the differential equations governing the evolution of particle velocity and stress along the characteristics. The present study employs an inherently stable finite difference representation of the characteristic equations, in which the spatial grid is obtained by evaluating the intersections in space-time of constant time lines with comparable increments of the characteristic variables. The numerical procedure is used to follow the propagation of a single-lobe sine pulse in cases where only ρ or c fluctuates spatially about a mean value while the other property is constant, and compares those results to the case were both material properties vary. Nonconstancy of c is shown to cause temporal shifts in waveforms, while spatial variation of ρc causes attenuation and distortion of the waveform.

scholarly journals Нелинейный фотоакустический отклик на механические напряжения вблизи отверстия в пластине из алюминиевого сплава Д16

2020 ◽  
Vol 46 (4) ◽  
pp. 22
Author(s):  
А.Л. Глазов ◽  
Н.Ф. Морозов ◽  
К.Л. Муратиков
Keyword(s):  
Aluminum Alloy ◽  
Laser Radiation ◽  
Thermal Effect ◽  
Modulation Frequency ◽  
Photoacoustic Signal ◽  
Theoretical Description ◽  
Mechanical Stresses ◽  
Electronic Subsystem ◽  
Sound Generation ◽  
Photoacoustic Effect

The features of the behavior of the photoacoustic signal depending on mechanical stresses near the hole in the plate made of aluminum alloy D16 are investigated. A new nonlinear photoacoustic effect was discovered, which consists in the appearance of a nonlinear component of the photoacoustic signal depending on mechanical stresses near the hole. This dependence is recorded in the signal at the modulation frequency of the laser radiation. A theoretical description of the discovered effect of sound generation by the thermoelastic mechanism in stressed metals is proposed basing on the consideration of the thermal effect of laser radiation on their electronic subsystem.

Photoacoustic signal with two heating sources: theoretical predictions and experimental results for the open photoacoustic cell technique

2020 ◽  
Vol 31 (7) ◽  
pp. 075202 ◽  
Author(s):  
Aloisi Somer ◽  
Anderson Gonçalves ◽  
Thiago V Moreno ◽  
Gerson Kniphoff da Cruz ◽  
Mauro L Baesso ◽  
...  
Keyword(s):  
Photoacoustic Signal ◽  
Experimental Results ◽  
Photoacoustic Cell ◽  
Open Photoacoustic Cell ◽  
Theoretical Predictions

Step-Scan FT-IR Photoacoustic Spectroscopy: The Signal Phase

1997 ◽  
Vol 51 (4) ◽  
pp. 552-557 ◽  
Author(s):  
M. W. C. Wahls ◽  
J. P. Toutenhoofd ◽  
L. H. Leyte-Zuiderweg ◽  
J. de Bleijser ◽  
J. C. Leyte
Keyword(s):  
Carbon Black ◽  
Polymer Films ◽  
Photoacoustic Spectroscopy ◽  
Photoacoustic Signal ◽  
New Method ◽  
Signal Phase ◽  
Photoacoustic Effect ◽  
Ft Ir ◽  
Phase Spectra ◽  
Pet Films

The model of Rosencwaig and Gersho for the photoacoustic effect is tested. The use of carbon black samples as a phase reference to estimate the apparatus phase φapp from the experimental signal phase φexp turned out to be ambiguous. A new method is presented to correct the experimental signal phases φexp of polymer films for the apparatus phase φapp. The photoacoustic signal phase of some well-defined poly(ethyleneterephthalate) (PET) films is obtained. As a phase reference, transparent thermally thick polymer films were found to be more convenient and dependable than carbon black samples. The resulting phase spectra of thermally thick and thermally thin PET films confirm the Rosencwaig–Gersho theory.

scholarly journals Iterative method for determination of the laser beam profile and τV-T

2008 ◽  
Vol 6 (1) ◽  
pp. 71-76
Author(s):  
Mihailo Rabasovic ◽  
Dragan Markushev
Keyword(s):  
Relaxation Time ◽  
Laser Beam ◽  
Photoacoustic Signal ◽  
Linear Process ◽  
Beam Profile ◽  
Photoacoustic Tomography ◽  
Spatial Profile ◽  
Photoacoustic Effect ◽  
Laser Beam Profile

Measuring the vibrational-to-translational relaxation time ?V-T in gases is one of the first applications of the photoacoustic effect. The spatial profile of the laser beam is crucial in these measurements because the multiphoton excitation is investigated. The multiphoton absorption is a non-linear process. Because of this, the top hat profile is preferable. It allows one to deal with nonlinearity in a simple manner. In order to reveal the real laser beam profile, we have slightly changed the theoretical profiles in such a manner that the best matching is obtained between theoretical and experimental photoacoustic signals. Still, there was a question: Is it possible to deduce the laser beam profile directly from the photoacoustic signal, thus avoiding manual changing of the laser beam profile? According to this paper, it is possible. The appropriate method has been found in another photoacoustics application: photoacoustic tomography. Thus, the method for the simultaneous determination of the spatial profile of the laser beam and vibrational-to-translational relaxation time is presented in this paper. It employs pulsed photoacoustics and an algorithm developed for photoacoustic tomography.

scholarly journals The antesonic condition for the explosion of core-collapse supernovae – II. Rotation and turbulence

2021 ◽  
Vol 502 (3) ◽  
pp. 4125-4136
Author(s):  
Matthias J Raives ◽  
Todd A Thompson ◽  
Sean M Couch
Keyword(s):  
Sound Speed ◽  
Rotation Period ◽  
Free Fall ◽  
Critical Value ◽  
Core Collapse ◽  
Central Mass ◽  
One Dimensional ◽  
Post Shock ◽  
State Models

ABSTRACT In the problem of steady free fall on to a standing shockwave around a central mass, the ‘antesonic’ condition limits the regime of stable accretion to $c_T^2/v_\mathrm{esc}^2\le 3/16$, where cT is the isothermal sound speed in the subsonic post-shock flow, and vesc is the escape velocity at the shock radius. Above this limit, it is impossible to satisfy both the Euler equation and the shock jump conditions, and the system transitions to a wind. This physics explains the existence of a critical neutrino luminosity in steady-state models of accretion in the context of core-collapse supernovae. Here, we extend the antesonic condition to flows with rotation and turbulence using a simple one-dimensional formalism. Both effects decrease the critical post-shock sound speed required for explosion. While quite rapid rotation is required for a significant change to the critical condition, we show that the level of turbulence typically achieved in supernova simulations can greatly impact the critical value of $c_T^2/v_\mathrm{esc}^2$. A core angular velocity corresponding to a millisecond rotation period after contraction of the proto-neutron star results in only a ∼5 per cent reduction of the critical curve. In contrast, near-sonic turbulence with specific turbulent kinetic energy $K/c_T^2=0.5-1$, leads to a decrease in the critical value of $c_T^2/v_{\rm esc}^2$ by ∼20 to 40 per cent. This analysis provides a framework for understanding the role of post-shock turbulence in instigating explosions in models that would otherwise fail and helps explain why multidimensional simulations explode more easily than their one-dimensional counterparts.

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