Photoacoustic methods

Detection of heat generated by absorbed radiation converted nonradiatively has also been done using pyroelectric materials like )3-poly(vinylidene) fluoride onto 

005 M HCIO4, scan rate 1 mV s, modulation frequency 125 Hz (based on data in [921]) 

A typical set of results as observed during the underpotential deposition and dissolution of lead onto a silver electrode is shown in Fig. 5.146. The increased absorptivity of the silver electrode covered with lead results in an increased photoacoustic signal. As the electrode potential is scanned only in the underpotential deposition region, the deposited amount of lead should correspond to a monolayer of atoms or a fraction thereof. Measurements of the photoacoustic signal as a function of time at various electrode potentials illustrate this point. At electrode potentials in the underpotential region the signal rises rapidly to a constant value. 

At more negative potentials, the signal rises continuously as a function of time, indicating bulk deposition. Accordingly, this method is capable of indicating depo- 

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This temperature rise can be detected directly (laser calorimetry and optical calorimetry), or indirectly by measuring the change in either the refractive index (thermal lensing, beam deflection or refraction and thermal grating) or the volume (photo- or optoacoustic methods). This review will focus primarily on photoacoustic methods because they have been the most widely used to obtain thermodynamic and kinetic information about reactive intermediates. Other calorimetric methods are discussed in more detail in a recent review.7... 

S. E. Braslavsky, G. E. Heibel. Time-Resolved Photothermal and Photoacoustic Methods Applied to Photoinduced Processes in Solution. Chem. Rev. 1992,92,1381-1410. 

The gas is another phase which is detectable by microphonic photoacoustic method. The focused beam (at Beam Line 15A (PF)) at wavelength of 1.56 A was used for this experiment. Photoacoustic cell for gas phase measurement is shown in Fig. 9. The optical path was 10cm (x6mm O with beryllium windows (18mm d>, 0.5mm... 

Photoacoustic method can be applied any types of shapes and states of the sample and also to non-destructive depth-profiling. Thus this finding expands the methodology of EXAFS much wider than before. High temperature super conductor, biological samples and other varieties can be studied. 

Photoacoustic imaging method is useful for the analysis of localization of various components in two-dimension and photoacoustic method has one more advantage that it can be applied to the non-destructive depth-profiling. Thus, in future, 3-dimensional analysis should be possible by this method. For the development of this possibility, the model experiments were performed. 

Figure 11.21 Schematic diagram of an experiment to measure absorption (using the photoacoustic method) and extinction.

Absorption by particles, for example acetylene smoke (Roessler and Faxvog, 1979a) and diesel emissions (Faxvog and Roessler, 1979), has been measured by the photoacoustic method. 

For completeness, we include in this brief survey a schematic diagram of the photoacoustic method (Fig. I4.2e), which has been discussed in Section 11.7. Absorption of chopped light by the particles gives rise to periodic heating which is detected acoustically. Scattered light does not contribute to the signal. 

FTIR reflectance and transmission spectroscopy is used for analysis of thin films. Nevertheless, due to the high absorptivities of mid-IR bands, the film thickness must be limited (up to 100 pm, depending on the specific bands chosen) in order to perform an accurate qualitative analysis. Other IR methods, such as attenuated total reflectance (ATR) and photoacoustic methods provide IR spectra of thick material, because they penetrate a very thin layer at the surface of a sample. However, is important to point out that the effective pathlength for the ATR and the photo-acoustic methods depends on the refractive index and thermal diffusivity, respectively. Therefore, the use of these techniques for the quantitative analysis of non-homo-geneous materials can be difficult. 

STRUCTURAL CONSOLIDATION. Structural consolidation of the plaster layer is necessary for protection against mechanical stresses, including seismic activity and vibrations generated by buses that bring visitors to the Valley of the Queens. The use of injectable polymers is a viable solution. The most stable polymers must be used, and it may be necessary to custom design polymers for this purpose. The integrity of the plaster layer, before, during, and after treatment must be determined and monitored by ultrasonic, piezoelectric, or photoacoustic methods. This procedure and the use of polymers for paint layer protection will require extensive controlled experimentation, especially on the physicochemical nature of the various pig-... 

The theory of rotation effects on prolate luminescent molecules in solution and its experimental verification have been developed and compared. Generalized diffusion equations for the rotational motion of an asymmetric rigid motor have been used to given an expression for steady-state fluorescence depolarization. " The radiationless transition from the first excited singlet state of Eosin has been measured by optoacoustic relaxation, and the absolute fluorescence quantum yields of organic dyes in poly(vinyl alcohol) have also been measured by the photoacoustic method. The accuracy of the method has been discussed in the latter paper. Actinometry in flash photolysis experiments has been assisted by new measurements on the extinction coefficient of triplet benzophenone. Matrix-isolation fluorescence spectrometry has been used to detect polycyclic aromatic hydrocarbons from gas chromatography. ... 

Some empirical methods have provided useful correlations concerning the effects of substituents on thermochemical properties of phenols. Griller and coworkers developed a photoacoustic method for measuring bond dissociation energies (BDE) of phenols and showed for the first time a linear relationship between the Hammett a+ para-substituent constant and BDEs. Wayner and coworkers found a correlation between experimental ABDE values for a series of substituted phenols compared with phenol and the Hammett a+ constants (equation 58). 

Eu(tta)3L2] and [Eu(bta)3L2] have been determined by photoacoustic methods.Although glass transitions of the vitrified mesophase could not be detected by luminescence measurements, photoacoustic spectra clearly showed this transition. 

The closely related photoacoustic method (wherein no wavelength dependency is taken... 

The idea of the experiment is illustrated in Fig.3. The upper part of the figure shows a simple cell filled with H2O. A slow gas flow is maintained at a constant pressure of about 40mTorr. The cell is irradiated by three different laser pulses, which follow each other within less than 50nsec. First an infrared laser at 2.7iJm is fired to vibrationally excite H2O and to prepare a well defined rotational state in the asymmetric stretch mode. The second laser., an excimer laser at 193nm, dissociates the H2O and the third laser analyses the formation of the OH products by LIF. The infrared excitation of H2O is monitored by the photoacoustic method with the microphone shown in the cell. At the short delays and the low pressures the products are analysed collision free. 

A very sensitive detection scheme is the photoacoustic method in combination with a multipass optical resonator, illustrated in Fig. 10.1. With this apparatus absorption coefficients down to o = 10 cm can be measured. 

Benedetto G, Boarino L, Spagnolo R (1997) Evaluation of thermal conductivity of porous silicon layers by a photoacoustic method. Appl Phys A Mater Sci Process 64 155-159... 

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