Grating technique

Consequently, instead of pulsing the photomultiplier tube, they leave the high voltage on and sensitize the following amplifier. Outside the sensitive interval they find that no appreciable signal is transmitted. With their scheme they are able to obtain time resolutions of around 0.5 /xsec. They also have the ability to handle intensity ratios of 104 to 1. As expected, this grating technique also reduces considerably the background noise. 

The transport coefficients have been measured by the transient holographic grating technique of Thermal Diffusion Forced Rayleigh Scattering (TDFRS) that has already been described in more detail in previous works [85-87] and will only be briefly sketched in the following (Fig. 1). 

The situation considered here should be applicable to experiments on spinodal decomposition in sufficiently thin polymer films with small periodic temperature modulations created by means of an optical grating technique or by local laser... 

Rogers JA, Fuchs M, Banet MJ, Hanselman JB, Logan R, Nelson KA. Optical system for rapid materials characterization with the transient grating technique application to nondestructive evaluation of thin films used in microelectronics. Appl Phys Lett 1997 71(2) 225-227. 

Abstract. A recently developed new method to monitor reaction kinetics of intermolecular interaction is reviewed. This method is based on the measurement of the time-dependent diffusion coefficient using the pulsed-laser-induced transient grating technique. Using this method, conformation change, transient association, and transient dissociation on reactions are successfully detected. The principle and some applications to studies on changes in the intermolecular interactions of photosensor proteins (e.g., photoactive yellow protein, phototropins, AppA) in the time domain are described. In particular, unique features of this time-dependent diffusion coefficient method are discussed. 

Brauchle s novel phase-modulated holographic grating technique has been successfully applied to excited molecules in poisoner matrices. 

Frez C, Diebold GJ, Tran C et al. (2006) Determination of thermal diffusivities, thermal conductivities, and sound speeds of room temperature ionic liquids by the transient grating technique. J Chem Eng Data 51 1250-1255... 

Abstract In this paper we address two aspects of ionic liquids (ILs) that to date have either no or limited studies. They are (1) exploitation of unique features of ILs to develop novel spectroscopic methods which otherwise is not possible and (2) development of novel spectroscopic methods for the sensitive and accurate determination of thermal physical properties of ILs. In the first category, we have successfully developed a novel, highly sensitive and accurate method for the determination of enantiomeric compositions of chiral compounds with different sizes, shape and functional groups including pharmaceutical products. This method is based on the use of a chiral IL which serves both as a solvent and also as a chiral selector. We have also demonstrated that ILs can be used to substantially enhance the sensitivity of thermal lens measurements. In the second category, we have demonstrated that transient grating technique and thermal lens technique can be used for the sensitive, accurate, nondestructive determination of thermal physical properties of ILs. 

DETERMINATION OF THERMAL PHYSICAL PROPERTIES OF IONIC LIQUIDS BY TRANSIENT GRATING TECHNIQUE... 

Theoretical treatment of photoacoustics and its application to the transient grating technique have been reported previously." The photoacoustic... 

TABLE 5. Themial Diffusivities (a). Sounds Speeds (c) and Damping Parameter (a) Determined by Transient Grating Technique Together with Some Reported Values. 

In summary, it has been demonstrated that the transient grating technique can be used to determine thennal physical properties (thermal diffusivity and thermal conductivity) of ILs. The technique has relatively high precision, namely relative errors are about 1%. It also has relatively high accuracy thermal conductivity values of ILs determined by this method agree, within 1% with values previously determined by other workers. More importantly. 

The transient absorption method utilized in the experiments reported here is the transient holographic grating technique(7,10). In the transient grating experiment, a pair of polarized excitation pulses is used to create the anisotropic distribution of excited state transition dipoles. The motions of the polymer backbone are monitored by a probe pulse which enters the sample at some chosen time interval after the excitation pulses and probes the orientational distribution of the transition dipoles at that time. By changing the time delay between the excitation and probe pulses, the orientation autocorrelation function of a transition dipole rigidly associated with a backbone bond can be determined. In the present context, the major advantage of the transient grating measurement in relation to typical fluorescence measurements is the fast time resolution (- 50 psec in these experiments). In transient absorption techniques the time resolution is limited by laser pulse widths and not by the speed of electronic detectors. Fast time resolution is necessary for the experiments reported here because of the sub-nanosecond time scales for local motions in very flexible polymers such as polyisoprene. 

In experiments currently in progress, the techniques used in this paper are being applied to the observation of local polymer dynamics in concentrated solutions and in the bulk. Measurements can be made on time scales as long as several triplet lifetimes ( 100 msec) because the transient grating technique utilizes absorption and not fluorescence. This long time window will allow the investigation of local motions in the bulk as a function of temperature from the rubbery state to the glass transition. 

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