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In this paper a photoacoustic senor for carbon dioxide and nitrous oxide detection is described which uses a quantum cascade laser. The sensor relies on a 4.43 μm continuous-wave room temperature quantum-cascade laser source and a homemade photoacoustic cell based on a cylindrical acoustic resonator. Primary laboratory tests have been performed for estimation of the achievable detection limits and possible applications for in situ and real time atmosphere measurements. It is demonstrated that the minimum detectable concentration of 13CO2 and N2O under laboratory conditions is 8 ppbv and 0.45 ppbv, respectively.

Thermal conversion (combustion, co-combustion, gasification and pyrolysis) appears to be the most promising alternative for sewage sludge management in the future. Nevertheless, safe and ecological usage of sewage sludge as a fuel requires information about their contamination. The aim of this paper is to present the photoacoustic spectroscopy (PAS) as a good method for contamination assessments of dried sewage sludge. Two types of granular sewage sludge: Sewage sludge 1 (SS1) taken from Polish wastewater treatment plant operating in the mechanical-biological system and sewage sludge 2 (SS2) taken from mechanical-biological-chemical wastewater treatment plant with phosphorus precipitation were analysed. The spectrophotometer FTIR Nicolet 6700 equipped with photoacoustic cell (Model 300, MTEC, USA) was used. The comparison with the most popular analytical methods (GC-MS) was also done. The results of PAS studies confirm the difference between the SS1 and SS2 which is in agreement with the GC-MS analysis. Higher absorbance was observed at each wavelength characteristics for the oscillator of chemical moieties for the SS1 with respect to the SS2.

Photoacoustic imaging using a closed photoacoustic cell and an open photoacoustic cell with gas- microphone detection scheme was described. R/G/B LED light sources were used for the closed photoacoustic (PA) cell configuration. The colored specimen enclosed in a PA cell was imaged with R/G/B color light sources, and an image restored from the inverted PA images was compared with the original image. For open cell configuration, an open PA cell using a spheroidal acoustic resonator was applied to measure the amount of large-sized colored specimens. A calibration curve for a food red dye was obtained that apparently showed the ability of the present scheme to measure as a spectroscopic measurement tool.

Thermal diffusivity (TD) of p-Si and Ag/p-Si samples were measured by photoacoustic technique using open photoacoustic cell (OPC). The samples were annealed by heating them at 960, 1050, 1200, and 1300 °C for 3 h in air. The thermal diffusivity of Ag-coated samples was obtained by fitting the photoacoustic experimental data to the thermally thick equation for Rosencwaig and Gersho (RG) theory. For the single layer samples, the thermal diffusivity can be obtained by fitting as well as by obtaining the critical frequency f c . In this study, the thermal diffusivity of the p-Si samples increased with increasing the annealing temperature. The thermal diffusivity of the Ag/p-Si samples, after reaching the maximum value of about 2.73 cm2/s at a temperature of 1200 °C, decreased due to the silver complete melt in the surface of the silicon.

Design of non-invasive and accurate novel methods for liver fibrosis diagnosis has gained growing interest. Different stages of liver fibrosis were induced in Wistar rats by intraperitoneally administering different doses of carbon tetrachloride. The liver fibrosis degree was conventionally determined by means of histological examination. An open-photoacoustic-cell (OPC) technique for the assessment of liver fibrosis was developed and is reported here. The OPC technique is based on the fact that the thermal diffusivity can be accurately measured by photoacoustics taking into consideration the photoacoustic signal amplitude versus the modulation frequency. This technique measures directly the heat generated in a sample, due to non-radiative de-excitation processes, following the absorption of light. The thermal diffusivity was measured with a home-made open-photoacoustic-cell system that was specially designed to perform the measurement from ex vivo liver samples. The human liver tissue showed a significant increase in the thermal diffusivity depending on the fibrosis stage. Specifically, liver samples from rats exhibiting hepatic fibrosis showed a significantly higher value of the thermal diffusivity than for control animals.

Localized, non-invasive cell stimulation has many applications. Here we show the initial proof-of-concept in vitro study of the photoacoustic cell stimulation approach, which is amenable to high-throughput screening applications. The proposed method is implemented as follows: 1) the localized excitation using the focused pulsed laser delivery on an absorptive material placed inside the well containing the cells, 2) cell stimulation by the photoacoustic pressure generated, and 3) fluorescence quantification of the membrane potential change over time. The preliminary proof-ofconcept in vitro study is conducted with primary neurons isolated from mouse cerebral cortex. The absorptive rubber media generates the photoacoustic pressure by the pulsed laser excitation. The experimental results show the feasibility of photoacoustic cell stimulation approach by indicating the significant membrane potential chance from the photoacoustically-stimulated primary neurons. Otherwise, the sham control without any photoacoustic stimulation shows minimal membrane potential change. We envisage that the proposed approach can allow broad strategies for noninvasive cell stimulation by using the photoacoustic contrasts situated at inside or outside of the body such as external absorptive materials or intravascularly-injected photoacoustic contrast particles.

A compact resonance photoacoustic cell with a Π-shaped internal cavity and a volume of ~0.2 cm3 is developed. The design of the cell and an experimental setup for testing its operational capabilities are described. Results are presented from tests of the photoacoustic cell in experiments to detect light absorption by ammonia in nitrogen flows using a single-mode diode laser with a wavelength of ~1.53 μm. The amplitude-frequency characteristics of the photoacoustic absorption response with and without ammonia are analyzed. The operation of the cell under conditions of resonance with the second longitudinal acoustic mode of the inner cavity of the cell (resonant frequency 4.38 kHz, Q-factor 13.9) is analyzed. The measured background signal level from the cell windows corresponds to an absorption coefficient of ~2.8·10–7 cm–1. The microphone-noise limited minimum detectable absorption is ~1.44·10–9 cm–1·W·Hz1/2.

The frequency response of a photoacoustic cell can be evaluated by measuring the output amplitudes point-by-point at different modulation frequencies, by measuring the pulse response, or by recording the cell response to a chirp stimulation, in which the light modulation signal sweeps within a given range of frequencies. This paper presents yet another method, in which the stimulation signal consists of a number of sine waves with different frequencies. A theoretical description is presented, and properties of the techniques are discussed and compared with the experimental results.

This paper describes the design and optimisation of the photoacoustic (PA) cell for nondestructive PA spectroscopy. The results of numerical calculations of the acoustic properties of the PA cell are compared with experimental measurements with respect to the frequency response and the quality factor of the cell. The method of designing and optimising of the PA cell is presented. Advantages and disadvantages of this study are discussed.

A homemade low-temperature, T shaped photoacoustic (PA) spectrometer is well established. The temperature stability and characteristics of the PA system in the temperature range of −90 to 0 °C were evaluated experimentally. A mathematical model for calculation of resonance frequencies and end-correction are proposed. The results of numerical calculations of the temperature dependent of resonant frequencies and the Q-factor of PA cell are compared with experimental measurements. The measured results show that the PA system has high Q-factor and the theoretical value is very well consistent with the experimental results. The variation of sensitivity of the PA system is very small in temperature range of −90 to 0 °C, which illustrates that the sensitivity of the microphone has little been affected by low temperature. So the system can be used in trace gas detection at low-temperature.

Photo-acoustic spectroscopy gas detection technology has the advantages of high sensitivity, good selectivity, small size and real time monitoring and has been widely used in environmental monitoring, industrial production, medical diagnosis, biological technology and monitoring of power facilities. In this paper, a method to improve the sensitivity of photo-acoustic spectroscopy system is presented, which is combined with the technique of Herriott type multiple pass cell. In this experimental apparatus, the design of the experimental device can make the beam pass the cell 18 times. By comparing the signal of one time pass through the photoacoustic cell and the signal of 18 times passes pass through the photoacoustic cell, we can confirm that the signal is increased and this method is feasible.

We present here the development and the characterization, in laboratory conditions, of our photoacoustic cell associated with QCL’s and specific readout circuit for gas traces sensing. Assessment has been done on CO2.

We describe the design and development of an injection seeded Nd:YVO4 laser for use in a differential fluorescence lidar for measuring atmospheric formaldehyde profiles. A high repetition rate Q-switched laser is modified to accept injection seed input to spectrally narrow and tune the output. The third harmonic output is used to excite formaldehyde (HCHO) fluorescence when tuned to a HCHO absorption line. Spectral confirmation is made with the use of a photoacoustic cell and grating spectrometer.

Chinese medicine is a historic cultural legacy of China. It has made a significant contribution to medicine and healthcare for generations. The development of Chinese herbal medicine analysis is emphasized by the Chinese pharmaceutical industry. This study has carried out the experimental analysis of ten kinds of Chinese herbal powder including Fritillaria powder, etc., based on the photoacoustic spectroscopy (PAS) method. First, a photoacoustic spectroscopy system was designed and constructed, especially a highly sensitive solid photoacoustic cell was established. Second, the experimental setup was verified through the characteristic emission spectrum of the light source, obtained by using carbon as a sample in the photoacoustic cell. Finally, as the photoacoustic spectroscopy analysis of Fritillaria, etc., was completed, the specificity of the Chinese herb medicine analysis was verified. This study shows that the PAS can provide a valid, highly sensitive analytical method for the specificity of Chinese herb medicine without preparing and damaging samples.

The determination of the frequency response of a photoacoustic cell is a typical activity during design and adjustment of a photoacoustic setup. The most common method of such measurements is based on point-by-point checking of the amplitude of the photoacoustic signal at different modulation frequencies. Such an approach can be time-consuming, especially if a lot of measurements at low modulation frequencies are to be performed. The article presents a method based on investigation of a photoacoustic response to short square pulse stimulation instead of continuous modulation of the light source. The method allows for measurements of the frequency response to be substantially shortened. A theoretical description and properties of the pulse measurement method are discussed and illustrated with a comparison of experimental results obtained from both frequency response measurement methods.

This paper discusses laser-induced photoacoustic investigations; it concerns a non-destructive technique for the determination of the thermal diffusivity of colon phantom tissue employing open photoacoustic cell configuration.

The use of a Helmholtz resonator as a photoacoustic cell has many advantages. Its main drawback in high-sensitivity photoacoustic measurements is the relatively low values of Q-factors of such cells. One of the important loss sources which limit the quality factor of photoacoustic Helmholtz resonators is the rapid change of the cross section at the cavity–duct boundaries. This paper presents a design of a cell in which the shape of the duct was modified in such a way that the cross-section change is more gradual. A presented comparison of measurements of the Q-factors shows clearly that the Q-factor of the cell can be improved by almost a factor of two by such a modification of the duct shape.