Detection photothermal deflection

Another type of IR gas-sensor has been reported by Cong et al. for the HTS of ethane ODH [12, 13]. They used a photothermal deflection (PTD) detector with a mass spectrometer because an electron-impact mass spectrometer cannot detect C2H4 concentrations at the ppm level in the presence of high concentrations of... 

Figure 3.35 Ethylene produced by oxidative dehydrogenation of ethane over Mo-V-Nb and Ni-Ce-Ta oxide catalyst libraries. The detection of ethylene was performed in a scanning mass spectrometer using a photothermal deflection method. Inactive Mo-V-Nb oxide catalyst (a) active Ni-Ce-Ta oxide library (b) [7] (by courtesy of Kluwer Academic Publishers).

Figure 7 Electrochemical photothermal deflection spectroscopy experiment (0.5 mol dm-3 Na2S04 pH = 10.5, 20 mV s 1), illustrating the detection of the onset of dissolution of nuclear fuel (U02) (A) voltammetric response for scans to various anodic potential limits (B) and (C) probe beam deflection for each scan. The deflection of the probe beam is proportional to the dissolved uranium concentration, and deflection of the probe beam towards the electrode surface is an indication that dissolution is occurring (Reprinted from Ref. 2 with permission from Elsevier Science S.A.)...

Photothermal deflection spectroscopy — Photothermal deflection is a photothermal spectroscopic technique used to detect the changes in the refractive index of the fluid above an illuminated sample by the deflection of a laser beam. There are two sources from which the thermal deflection effect might appear. One of them is produced by a gradient in the refractive index after a thermal excitation where the density also varies with temperature, in the so-called mirage effect. And the other one is produced by the topographical deformation of the surface over which the laser beam is reflected. This effect is known as photothermo-elastic effect or surface photothermal deflection [i]. 

While the MIPs used in this work were inherently stable for at least 1 year, the silver films were prone to atmospheric degradation. Indeed, it was found that the application of the MIPs to the film protected it to some extent, but even when stored in vacuo these substrates were only stable for 5 days. The use of gold substrates is reportedly under investigation. Finally, it must be noted that the equipment used in this work was not a simple off-the-shelf commercial SPR system. These custom-made systems employed either highly sensitive photothermal deflection spectroscopy or a photodiode array to detect the changes in resonance... 

One way of measuring true absorption is to employ photothermal deflection spectroscopy (see Fig. 9-1). In this case the absorbed light, leading to a slight heating up of the sample, is detected by the temperature-dependent deflection of a laser beam passing close by the sample. The obvious advantage of this method is that it really measures the absorption coefficient (a). 

The ethylene trap collects all the produced volatile hormone for a certain period so that small production rates become detectable. Transitory features are thus lost. Very sensitive laser-based ethylene monitors become then advantageous. Using a laser-driven photoacoustic (PA) ethylene detector coupled to a flow-through setup, a detection limit of 6pl/l is reached with a response time of 4 min at a flow of ll/h (Harren et al. 1990a). The photothermal deflection (PTD) instrument monitors ethylene concentrations down to 0.5 nl/1, locally, much faster (Is) and non-intrusively. In this way, ethylene production, e.g. by fruits, can be measured non-destructively. Very recently, we have improved the time... 

Huelin FE, Kennett BH (1959) Nature of the olefins produced by apples. Nature 184 996 Jackson WB, Amer NM, Boccara AC, Fournier D (1981) Photothermal deflection spectroscopy and detection. Appl Opt 20 1333-1344... 

Figure 5 Calibration curves for the dinitrophenol herbicide DNOC in aqueous solution when using different techniques (A) PDS Photothermal deflection spectroscopy, (B) TL thermal leasing, (C) PIS Photothermal Interferometric spectroscopy, (D) PAS a photoacoustic spectroscopy, (E) a conventional spectrophotometer Cary 2400. Reproduced with permission of SPIE from Faubel W (1997) Detection of pollutants in liquids and gases. In Mandelis A and Hess P (eds) Life and Earth Sciences. Progress in Photothermal and Photoacoustic Science and Technology, Vol III, Chapter 8. Bellingham SPIE.

In a related approach, the heat flow is detected optically [photothermal deflection spectroscopy). A representative setup is shown in Figure 5. The prism/metal assembly is placed upon a rotation stage, and SPs are excited in the usual way. Heat... 

The technique employed is IR-FT photothermal beam deflection spectroscopy (PBDS). It is an off-shoot of photoacoustic spectroscopy (PAS) [1] and is based on the "mirage detection of the photothermal effect invented by Boccara et al. [2] and shown to result in a spectroscopic technique of remarkable versatility and utility. Some applications of "mirage spectroscopy," mainly in the visible, and theoretical treatments, have been described [3 6]. The method has now been developed for use in the IR. The spectrometer and techniques are described in detail elsewhere [7], but it will be useful to give a brief outline of the principles. 

The feasibility of thermic and calorimetric detection of the absorbed radiation has been mentioned in the context of grazing-incidence experiments. This is quite close to the class of photothermal techniques with which a number of different detection schemes is employed (Coufal, 1986). Out of these, photoacoustic spectroscopy (PAS) is frequently used in infrared spectroscopy (Graham et al., 1985 Urban et al., 1990 McClelland, 1992) while inspite of its potential, thermal beam deflection has not yet found as many applications as in other spectral ranges, possibly due to the lower availability of suitable lasers (Low and Morterra, 1985). 

An alternative technique is the so-called Photothermal Beam Deflection Spectroscopy [PBDS], based on the so-called mirage effect first reported by Boccarra and coworkers [39, 40]. In this case, the periodic temperature rise caused by the absorption of the modulated IR radiation (i.e. the photothermal effect) is detected optically because it causes periodic deflections of a laser beam passing close to the surface of the solid sample. The PBDS technique has some advantages over the PAS technique, because of its lower Hmits of sample dimensions, but it has disadvantages because of the critical geometric setup. Like PAS, PBDS can have advantages with respect to traditional IR technique for the detection of surface... 

Basically, there are two categories of FTIR spectroscopies reflection and nonreflection techniques [38], The latter class comprises either acoustic detection or emission from the sample itself. The techniques recognized here are photoacoustic spectroscopy (PAS), emission spectroscopy (EMS), and photothermal beam deflection spectroscopy (PBDS). These techniques will not be considered further in this chapter. The reader is referred to the literature [39-42], For adhesion studies the reflection techniques (SRIRS) are more important. The major classes of sampling techniques in SRIRS are ... 

Infrared Photothermal Beam Deflection Spectroscopy Infrared photothermal beam deflection spectroscopy (IR-PDS) is better than PAS because it does not have a microphone near the sample. It involves two light sources. One is an interferometer that produces modulated radiations to illuminate the sample, and the other is a laser source that is placed so that its beam grazes the surface of the carbon sample. The absorption of the incident-modulated radiation beam by the sample produces heat, causing thermal gradients that deflect the laser beam. The deflected laser beam is detected by the detector, and the signal reproduced is a measure of the photothermal effect induced on the sample surface. The resulting... 

Figure 5 Basic photothermal detection setup. The position of the deflected beam of a probe laser PL is measured by a position-sensitive detector PSD.

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