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Plasmonic nanoparticles can be used in photothermal therapy thanks to their ability to generate local heat. The light-to-heat conversion efficiency is crucial for therapeutic and diagnostic applica...

The detection sensitivity of optoacoustic spectroscopy at the short-wavelength infrared (SWIR) region is reduced by water absorption in aqueous solutions. Our work reports marked improvements in the sensitivity of optoacoustic spectroscopic measurements of proteins, lipids, and glucose when performed at 4 °C, compared to conventional optoacoustic or IR spectroscopy. Studying the effect of water temperature on optoacoustic signals revealed a polarity change at temperatures below 4 °C (muting temperature). The dependence of the optoacoustic signal and the muting temperature on sample concentration were further investigated, demonstrating that changes in these dependencies enable accurate quantification of the solute concentration.

Review sums up the application of photoacoustic and photothermal spectroscopies for the analysis and characterization of soils and soil organic matter and discusses the outlooks in this area. Keywords: Photoacoustic spectroscopy, Optoacoustic spectroscopy, Photothermal spectroscopy, Probe microspectroscopy, Soil, Soil organic matter, Dispersed organic matter

Agradecimentos: This work was supported by research grants SIP-IPN (20170545 and 20181764) and CONACyT (2015-02-1042, 264093, 2016-01-2482). A. M. M. acknowledges the support of the Brazilian Agencies CNPq and FAPESP. The support of COFAA-IPN by the SIBE and BEIFI programs is also acknowledged Abstract: The phase-resolved method has been widely used in photoacoustic spectroscopy for separating the contribution of different optical absorption centers to a spectrum. However, the procedure is lengthy, tedious and without precision control, because one has to calculate several spectra to search for the phase angle at which only one contribution is present every time. In this work, this limitation is avoided by the implementation of a method as a search and optimization problem using the Hill Climbing Metaheuristic Algorithm. As test examples, the photoacoustic spectra of chilli fruit skin of Anaheim type (Capsicum Annuum L.) and yellow corn grain pericarp of dent type (Zea Mays L.) were analyzed in the wavelength ranges where there is optical absorption of the photoprotective pigments of these samples CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Using a model system, the applicability of the frontal configuration of optoacoustic spectroscopy in analytical practice is shown. An optoacoustic cell made using layered-prism geometry was designed and tested; it ensures operation with a layer thickness of 20–100 μm and sample volumes of 50–100 μl. Conditions are proposed for determining iron(II) in the form of tris(1,10-phenanthrolinate) with the detection limit of 3 × 10−7 M, which is less that the detection limit under similar induction conditions and for the same determination procedure using thermal-lens spectrometry (4 × 10−7 M). The determination has high reproducibility (relative standard deviation for 10−6 M is 0.005) and expressivity (1 min per sample detection).

In this paper a spectroscopic characterisation method based on the optoacoustic technique has been used to investigate the optical properties of two separate spherical gold nanoparticle (SGNP) solutions where an absorption peak located at 520 nm has been observed. This analysis has been carried out over the visible wavelength range from 410 to 650 nm using a Q-switched Nd:YAG pumped optical parametric oscillator (OPO). To verify the reliability of optoacoustic spectroscopy (OAS), the results obtained have been compared to those from more standard and limited spectrophotometer and reference collimated optical transmission schemes, where good agreement is shown. The experimental procedure presented here demonstrates the potential of this technique for integration along with optoacoustic imaging methods to identify physiological information for non-destructive in-vivo applications.

The cis -skew to trans -planar photoisomerization of benzil in the photoexcited state was studied by laser-induced optoacoustic spectroscopy (LIOAS) in a series of normal alkane solvents at room temperature. The structural volume change due to the photoisomerization process has been estimated and compared with the same calculated from the optimized skew and trans structures. The magnitude of the structural volume change is estimated to be 22.9 ± 1.2 mL/mol. This study reveals that an expansion in volume occurs during the photoinduced isomerization process. In non-polar alkane solvents, the estimated volume change has been argued to be free from electrostrictional contribution.

Background: Anemia is an underdiagnosed, significant public health concern afflicting >2 billion people worldwide. The detrimental effects of tissue oxygen deficiency on the cardiovascular system and concurrent appearance of anemia with numerous high-risk disorders highlight the importance of clinical screening. Currently there is no universally accepted, clinically applicable, noninvasive hemoglobin/hematocrit screening tool. The need for such a device has prompted an investigation into a breadth of techniques. Methods: A synopsis of the literature and current directions of research in noninvasive total hemoglobin measurement was collected. Contributions highlighted in this review are limited to those studies conducted with a clinical aspect, and most include in vivo patient studies. Results: The review of potential techniques presented here includes optoacoustic spectroscopy, spectrophotometric imaging, diffuse reflectance spectroscopy, transcutaneous illumination, electrical admittance plethysmography, and photoplethysmography. The technological performance, relative benefits of each approach, potential instrumentation design considerations, and future directions are discussed in each subcategory. Conclusions: Many techniques reviewed here have shown excellent accuracy, sensitivity, and specificity in measuring hemoglobin/hematocrit, thus in the near future a new clinically viable tool for noninvasive hemoglobin/hematocrit monitoring will likely be widely used for patient care. Limiting factors in clinical adoption will likely involve technology integration into the current standard of care in each field routinely dealing with anemia.

This chapter provides the molecular constants for (003) and (005) states of triatomic HD16O (H16OD) molecule measured using intracavity laser absorption spectroscopy, optoacoustic spectroscopy and theoretical calculation.

The electron-transfer reaction between the erythrosin dianion triplet, 3Er2-, and Mo(CN)84- was studied by laser-induced optoacoustic spectroscopy in the presence of various cations (Li+, Na+, K+, and Cs+, all at 4.4 × 10-2 M analytical concentration). The buffer was in each case the corresponding H3BO3/B(OH)4-,M+ (pH 9.18 at 20 °C). The enthalpy level of the triplet 3Er2- is ΔH1 = 180 ± 10 kJ mol-1 independent of the cation. The structural volume change for 3Er2- formation is ΔV1 = ca. 2 mL mol-1, attributed to intrinsic changes upon its formation. The formation of the redox products Er3- + Mo(CN)83- also leads to an expansion, ΔV2, between 12 mL mol-1 for Li+ and 8 mL mol-1 for Cs+, which linearly correlates with the heat released during the radical formation step. The correlation is interpreted in terms of an enthalpy−entropy compensation effect, due to the strong influence of the cations on the H-bond water network, also reflected in the correlation between ΔV2 and the literature values for the abilit...

We have developed an optoacoustic spectroscopy technique for noninvasive hematoma diagnostics and oxygenation monitoring with high resolution and accuracy. We will report results of our animal and clinical studies on these important applications.

Reaction volume changes, ΔVR, enthalpy content, ΔHMLCT, and decay lifetimes, τ2, of the metal-to-ligand charge transfer (MLCT) complex of (2,2‘-bipyridine)tetracyanoruthenate(II) complex, Ru(bpy)(CN)42-, inside the water pools of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles dispersed in n-alkanes, were determined using laser-induced optoacoustic spectroscopy (LIOAS). Emission quantum yields, Φem, of the complex were also determined by steady-state measurements. The enthalpy content of the MLCT state of Ru(bpy)(CN)42- was not dependent on the amount of water inside the reverse micelles (defined as the molar ratio R = [H2O]/[AOT]) and was, within experimental error, similar to that in water. However, the values of τ2 and Φem decrease while those of ΔVR increase as the values of R are incremented from 3 to 10. At the larger R values, τ2, Φem, and particularly ΔVR resemble the values in neat water. These results are interpreted to arise from the type of water involved in the hydrogen bond int...

Laser-induced optoacoustic spectroscopy (LIOAS) has been used for the quantitative analysis of pH and/or CO 2 in aqueous solutions. This technique implies the precise measurement of spectral variations of indicator dyes adsorbed on surfaces (e.g., polymer membranes). Optimization of the pH-sensitive membrane and of the sensor module leads to promising results due to the higher sensitivity of LIOAS in comparison with the conventional analysis by reflection spectroscopy.

Laser induced optoacoustic spectroscopy has been used to determine the relative contribution of the intersystem crossing and internal conversion to the non-radiative energy dissipation from the two excited ICT probes p-N,N-dimethylaminobenzonitrile (DMABN), and p-N,N-dimethylaminobenzaldehyde (DMABA) in solvents of different polarity. It is observed that while intersystem crossing is the main non-radiative deactivation process for DMABN in all the solvents studied this is not the case in polar solvents for DMABA.

A set of calorimetric references for excitation at λ = 266 nm in acetonitrile solutions is proposed. Theophylline and several purinic compounds (purine, 6-methylpurine, 6-methoxypurine, 6-chloropurine, and 6-aminopurine) were investigated using pulsed laser optoacoustic spectroscopy with resolution times between 150 ns and 1 μs and compared with 2-hydroxybenzophenone. At room temperature, all these compounds show no fluorescence, good stability and no photochemical processes as photodegradation or multiphotonic effects below fluences of 1000 J/m 2 .

It is important to identify patients with chronic obstructive pulmonary disease (COPD) and lung cancer in the early stages of the disease. The method of laser opto-acoustic gas analysis, in this case, can act as a promising tool for diagnostics. The material for this study were the gas emission samples collected from patients and healthy volunteers – samples of exhaled air, swabs from teeth and cheeks. A set of material was formed three groups: healthy volunteers, patients with COPD, lung cancer patients. The resulting samples were analyzed by means of laser opto-acoustic gas analyzers: with intracavity location detector (ILPA-1), with extracavity location detector (LGA-2). Presentation of the results in an easy to visual form was performed using the method of elastic maps, based on the principal component analysis. The results of analysis show potentialities of usage of laser optoacoustic spectroscopy application to assess the status of patients with chronic obstructive pulmonary disease and lung cancer.

An optoacoustic technique for solutions of strongly light-absorbing analytes at 0.1-0.01 mol l(-1) is proposed. The technique is based on the wide-band forward mode detection of temporal profiles of laser-generated ultrasonic pulses (optoacoustic signals). The leading edge of the signal repeats the distribution of the laser fluence in the medium, which makes it possible to determine its optical absorption and investigate its dynamics during a reaction. The range of light-absorption coefficients starts from 1 to 5 and reaches 10(4) to 10(5) cm(-1). The determination of iron(II) as ferroin shows the possibility of probing 0.1 mol l(-1) of iron(II), which was not previously achieved for this reaction by optical spectroscopy. To further prove the concept, kinetic measurements for ferroin decomposition at the level of 0.1 mol l(-1) and at high pHs are performed. The results are compared with spectrophotometry at lower concentrations and show good reproducibility and accuracy of kinetic constants.

We have developed an optoacoustic technique for noninvasive cerebral and central venous oxygenation monitoring. Our data indicate that optoacoustics can provide noninvasive, accurate, continuous monitoring of cerebral and central venous oxygenation.

The feasibility of applying optoacoustic spectroscopy for the detection of short-lived species is demonstrated. Several reaction intermediates were observed in a dc discharge. The method was shown to be significantly more sensitive than direct absorption and is complementary to existing techniques for the monitoring of transient species.

Optoacoustic spectroscopy detection is one of the newest detection methods. It can detect the weak-absorbed specimen with high-sensitivity. In this treatise, the technique is applied to detect the water quantity in oil. There are two spectral absorbing wave bands of water, so the innovation of this project lies in adopting laser sources with two different wave bands. This can effectively strengthen the signal intensity of optic acoustic effect and increase the rate of Signal-to-Noise. Adopting the ARM embedded-system to collect data can help to enormously reduce the hardware bulk of the instrument. This project has adopted the wavelet-analyzing method to fulfill the wave-filtering and noise-cleaning for the experiment result, established the mathematical model. It is proved that the detecting result is validity.

The limited penetration depth of optical energy in biological media is primarily due to the high level of optical scattering. This optical attenuation places an upper limit on optical, diagnostic, and therapeutic techniques for in in-vivo applications. The optoacoustic technique combines the unique advantages of light and sound, providing high levels of contrast, while maintaining the spatial resolution of acoustic techniques. The importance of colloidal gold solutions, as optical contrast agents in optoacoustic biomedical applications, is to increase the absorption of optical energy in areas where scattering is dominant and has prompted the study presented in this thesis on their characterization and quantification. It has been demonstrated that the acoustic transients generated from the optical irradiation are directly proportional to the wavelength dependent absorbed optical energy. Advantage has been taken of this fact to design two separate optoacoustic schemes. The first has been implemented to quantify the optical absorption, at a single laser wavelength, of spherical gold nanoparticles embedded within a medium that simulates the high scattering nature of soft tissue. The second has been designed to obtain the spectroscopic profile of such gold nanostructures. The results obtained from the optoacoustic analysis are compared to those from a reference measurement scheme, based on collimated optical transmission, which is in parallel and under the same conditions. This comparative analysis has confirmed the interest for the proposed technique of optoacoustics for laser spectroscopy of gold nanoparticles. In this thesis results obtained, for the first time, on the quantification and spectroscopic analysis of gold nanoparticles embedded in a liquid phantom using the optoacoustic technique are presented. The results have been confirmed by the reference measurement scheme and an offline commercial spectrophotometer. To further demonstrate the potential of the optoacoustic technique, information regarding the position and dimensions of the absorbing solutions have been extracted from measurements. The spectroscopic analysis has been carried out in steps of 5 nm over the complete wavelength range from 450 nm to 650 nm for a spherical gold nanoparticle solution and 410 nm to 1000 nm for a gold nanorod solution. This research work has opened up new lines of investigation in the field of monitorization of nanoparticle contrast agents embedded in biological media for optoacoustic diagnostics and biomedical applications., La limitación que existe en la profundidad de penetración de la energía óptica en medios biológicos se debe en principalmente al alto nivel de scattering (dispersión) óptico que éstos presentan. Esta atenuación óptica impone un límite superior que condiciona el uso de técnicas ópticas tanto en el campo del diagnóstico como en aplicaciones terapéuticas in vivo. La técnica optoacústica combina las ventajas que tienen la luz y el sonido, ofreciendo altos niveles de contraste, a la vez que garantiza la resolución temporal que ofrecen las técnicas acústicas. Las soluciones coloidales de oro permiten aumentar la absorción de la energía óptica. Este efecto puede ser utilizado como agente de contraste óptico en las técnicas optoacústicas donde hay medios con un alto nivel de scattering óptico. Este fenómeno ha motivado su caracterización y cuantificación en esta tesis. En esta tesis se ha demostrado que los transitorios acústicos generados a partir de la irradiación óptica son directamente proporcionales a la energía óptica absorbida y a su longitud de onda. Aprovechando este hecho, se ha diseñado dos sistemas optoacústicos. El primero se ha implementado con el objetivo de cuantificar la absorción óptica, en una única longitud de onda, de las nanopartículas esféricas de oro embebidas en un medio con alto nivel de scattering que modela las propiedades ópticas de tejidos blandos. El segundo esquema ha sido diseñado para conseguir el perfil espectroscópico de dichas nanopartículas de oro. Los resultados obtenidos del análisis optoacústico se han comparado con los resultados proporcionados por un sistema de medida de referencia, basado en la transmisión óptica, que funciona en paralelo con el sistema optoacústico y bajo las mismas condiciones experimentales. Este estudio comparativo ha confirmado el interés de las técnicas optoacústicos para aplicaciones en espectroscopia laser para nanopartículas. En este trabajo de tesis se presenta por primera vez resultados sobre la cuantificación y el análisis espectroscópico de nanopartículas de oro embebidas en un fantom liquido utilizando técnicas optoacústicos. Los resultados han sido confirmados por las medidas de referencia y también por los datos ofrecidos por un espectrofotómetro comercial. Para profundizar en el potencial de la técnica optoacústica, se ha conseguido extraer información relacionada con las dimensiones y posición de la solución absorbente partiendo de las medidas realizadas. El análisis espectroscópico se ha llevado a cabo realizando adquisiciones en pasos de 5 nm a lo largo del rango de longitudes de onda que va desde los 450 nm hasta los 650 nm para nanopartículas esféricas y en el rango que se extiende entre los 410 nm y los 1000 nm para la solución de nanorods de oro en un medio de alto nivel de scattering óptico. Este trabajo de tesis doctoral ha abierto nuevas líneas de investigación en el campo de la monitorización de nanopartículas como agentes de contraste óptico embebidos en medios biológicos para el diagnóstico mediante técnicas optoacústicos y aplicaciones biomédicas.

Oxidative-based diseases including diabetes, chronic renal failure, cardiovascular diseases and neurological disorders are accompanied by accumulation of advanced glycation endproducts (AGE). Therefore, AGE-associated changes in tissue optical properties could yield a viable pathological indicator for disease diagnostics and monitoring. We investigated whether skin glycation could be detected based on absorption changes associated with AGE accumulation using spectral optoacoustic measurements and interrogated the optimal spectral band for skin glycation determination. Glycated and non-glycated skin was optoacoustically measured at multiple wavelengths in the visible region. The detected signals were spectrally processed and compared to measurements of skin auto-fluorescence and to second harmonic generation multiphoton microscopy images. Optoacoustic measurements are shown to be capable of detecting skin glycolysis based on AGE detection. A linear dependence was observed between optoacoustic intensity and the progression of skin glycation. The findings where corroborated by autofluorescence observations. Detection sensitivity is enhanced by observing normalised tissue spectra. This result points to a ratiometric method for skin glycation detection, specifically at 540 nm and 620 nm. We demonstrate that optoacoustic spectroscopy could be employed to detect AGE accumulation, and possibly can be employed as a non-invasive quick method for monitoring tissue glycation.

We present a photoacoustic sensor for VOC's based on a room-temperature DFB-diode laser. Detecting certain

The volume changes accompanying triplet state formation, decay and quenching in aqueous solution were followed by temperature-dependent, laser-induced, optoacoustic spectroscopy (LIOAS) measurements. The origin of these volume changes mainly involves specific solvent-solute interactions, which are different in the triplet state than in the parent ground state.

In this work we present results of an investigation on Doppler limited infrared absorbing transitions of CHD2OH by optoacoustic detection. It is an alternative and attractive technique to be applied to this methanol isotopomer, in comparison to Fourier transform spectroscopy. Using a waveguide CO2 laser of 290 MHz tunability on each line, we were able to observe 60 IR absorptions, most of them of large offset. The data will be useful in the theoretical analysis of this molecule, as well as in the generation of far-infrared (FIR) laser radiation in optically pumped molecular lasers FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado

We investigated the behavior of infrared (IR) absorption laser transitions of methanol isotopes in the presence of an uniform electric field, in order to determine Doppler-free spectroscopic data such as homogeneous linewidth and saturation parameter. For this we combine photoacoustic detection with the high resolution provided by the Nonlinear Hanle Effect (NLHE) on molecular transitions FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: Work supported by: FAPESP, CNPq, FBB, FAEP-Brasil Abstract: In this work we present results of an investigation on Doppler limited infrared absorbing transitions of CHD2OH by optoacoustic detection. It is an alternative and attractive technique to be applied to this methanol isotopomer, in comparison to Fourier transform spectroscopy. Using a waveguide CO2 laser of 290 MHz tunability on each line, we were able to observe 60 IR absorptions, most of them of large offset. The data will be useful in the theoretical analysis of this molecule, as well as in the generation of far-infrared (FIR) laser radiation in optically pumped molecular lasers FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Time-resolved laser-induced optoacoustic spectroscopy (LIOAS) is a sensitive photobaric method for nondestructive probing of materials that monitors the pressure changes induced in a liquid or a solid sample after photoexcitation with a pulsed laser. LIOAS is an interesting tool for investigating photo-induced chemical processes as well as ‘optically silent’ intermediates, i.e., those displaying no changes in absorption or emission. A phenomenological approach to the equations related to this technique is employed and a description is given of the equipment and data handling as well as a few examples of applications of LIOAS to small molecules either in solution or in a solid powder matrix.

One of the challenging problems in the BR cycle is the accurate determination of the photochemical quantum yield for the reaction of BR yielding its early intermediates, J and K. Due to the strong overlap between the absorption spectra of BR and K [1], it is difficult to obtain this yield through optical methods. Sub-ps LIOAS circumvents this problem by measuring the heat stored after excitation with a laser pulse, affording thus the quantum yield of the species storing the energy for a time longer than the heat integration time of the experiment.

Pulsed laser optoacoustic detection system is being developed to monitor SO2, NOx, NH3, CO, CO2, H2O, O3 gases. The gases will be analysed using UV-VIS and IR sources. Results obtained with the UV-VIS system will be described herein.

A specimen of foam graphite foil is shown to have an anisotropic structure and consist of layers (stacks) of crystallite sheets weakly bound to one another.

An apparatus for resonant optoacoustic spectroscopy is described. The dispersion of the acoustic resonance frequency and the variation of the frequency bandwidth was studied as a function of pressure in the vibrational relaxation region for pure CH4 and mixtures with Xe and H2. These measurements yield the corresponding relaxation times and a better understanding of the dissipation effects caused by energy transfer processes. The role played by other loss mechanisms is also discussed. In der vorliegenden Arbeit wird eine Apparatur zum Studium resonanter optoakustischer Spektren beschrieben. Sowohl die Dispersion der akustischen Resonanzfrequenz als auch die Variation der Bandbreite der Resonanzkurven werden im Bereich der Schwingungsrelaxation als Funktion des Druckes fur reines CH4 und Mischungen von CH4 mit Xe und H2 untersucht. Die Messungen liefern die entsprechenden Relaxationszeiten und ein besseres Verstandnis der durch Energieubertragungsprozesse verursachten Dissipation. Die Effektivitat anderer Dampfungseffekte in einem akustischen Resonator werden ebenfalls diskutiert.

This paper contains a review of results of the experimental investigation of linear and nonlinear absorption of atmospheric gases using the methods of multichannel optoacoustic spectroscopy with pulsed visible and IR lasers.

An investigation has been made of the sensitivity of the optoacoustic technique in conjugation with a cw dye laser for the detection of forbidden molecular transitions. Calibration with the a 3 A 2 - X 1 A 1 transition of thiophosgene, Cl 2 CS, shows that th technique could be used to study band systems with oscillator strengths of f = 10 −10 . The method has been applied to the detection of two recently observed forbidden transitions of thioformaldehyde, H 2 CS, and a previously unreported transition of disulphur monoxide, S 2 O. A vibrational analysis is presented for the S 2 O transition, which has upper state frequencies of v ′ 1 ≈ 1076 cm −1 , v ′ 2 ≈ 449 cm −1 302 cm −1 . The origin of the system has not been located, but cannot be at higher frequency than 14200 cm −1 . The transition has an oscillator strength of ≈ 10 −6 , and is assigned to a triplet-singlet transition by its close analogy to the transition of NSF in the same spectral region.

The Doppler-free optoacoustic spectrum of the oxygen-18 species of methanol has been investigated with a CO2 laser. Seventeen coincidences have been found between infrared absorptions of CH183OH and CO2 laser lines. The strongest feature seen, pumped by the 10R(20) CO2 laser line, has two plausible alternative identifications, determined from a parallel high-resolution spectroscopic study of the C-O stretching band. Further experimental tests are suggested to resolve the assignment, and predicted far-infrared laser frequencies are given for the two possibilities.

The value of optoacoustic spectroscopy as a technique for the quantitative non-destructive determination of thickness of surface layers is examined by reference to two systems. In one, carbon deposits on a nickel-alumina catalyst with graphite filler, it is shown that the deposit can be detected, and its thickness estimated by application of a simple equation. The relationship does not hold for different thicknesses of the transparent polymer melinex above 40 μm. It is argued that because the optoacoustic signal has complex origins, reliable quantitative relationships are difficult to establish. However, it is confirmed that qualitative analysis of subcutaneous layers by OAS, is relatively straightforward.

We report high‐resolution absorption spectroscopy of powdered microsamples using a pulsed laser and a gated optoacoustic detection technique. Our method is simple, sensitive, and easily adaptable for cryogenic cooling of the sample. Quantitative data for Ho2O3, Dy2O3, and Er2O3 powdered crystals are obtained, and identification and analysis of the observed spectral lines are given for Dy2O3 and Er2O3.

We report the observation of saturation Lamb-dips in the optoacoustic spectrum of CH 3 OH and CO 2 excited by CO 2 laser. An intermodulation technique is used to get Doppler-free resolution of the lines. Because of the small sample size and the high sensitivity intermodulated optoacoustic spectroscopy compares favorably with other Doppler-free methods.

Optoacoustic spectroscopy (OAS) is based on measuring the OA signal as a function of wavelength of the monochromatic radiation impinging on the sample. In this chapter we consider mainly the general experimental techniques and potentialities of laser OAS of gaseous media.