Optical intensity

The first intravascular sensor for simultaneous and continuous monitoring of the pH, pC>2, and pCC>2 was developed by CDI-3M Health Care (Tustin CA)14 based on a system designed and tested by Gehrich et al.15. Three optical fibres (core diameter = 125 pm) are encapsulated in a polymer enclosure, along with a thermocouple embedded for temperature monitoring (Figure 3). pH measurement is carried out by means of a fluorophore, hydroxypyrene trisulfonic acid (HTPS), covalently bonded to a matrix of cellulose, attached to the fibre tip. Both the acidic ( eXc=410 nm) and alkaline ( exc=460 nm) excitation bands of the fluorophore are used, since their emission bands are centred on the same wavelength (/-cm 520 nm). The ratio of the fluorescence intensity for the two excitations is measured, to render the sensor relatively insensitive to fluctuations of optical intensity. 

Figure 11 plots the SNR versus filter bandwidth, at 3 levels of received optical intensity. It may be observed that the SNR is not very dependent on filter centre wavelength, but is more strongly related to the bandwidth of the optical filter. Optimum SNR is attained with an optical filter bandwidth of approximately 80-100 nm, i.e. significantly wider than the very narrow bandwidth that was found to maximise the modulation index. 

Non-linear optical interactions occur in materials with high optical intensities and have been used to produce coherent light over a wide range of frequencies from the far infra-red to the ultra-violet. The three wave mixing process is of particular interest as it can be used for optical parametric amplification and optical second harmonic generation (SHG) and occurs in non-centrosymmetric materials. 

To determine optical damage in bulk benzil crystals a Q-switched Nd YAG laser with 1KW peak power, pulse width of 0.1 ps and pulse repetition rate of 500Hz was used. The laser power was attenuated using a set of neutral density filters and focussed onto a bulk benzil crystal using a x10 microscope objective. No optical damage was observed with optical intensities of upto 100MW/cm - Also, no optical damage was observed in benzil cored fibres with similar optical intensities. 

It is often desirable to immobilize different biomolecules on different sensing elements in close proximity on the same nanophotonic sensor in the development of a multiplexed sensor. This is the case in the example of parallel ID photonic crystal resonators described in Sect. 16.4. Cross-contamination of biomolecules must be avoided in order to preserve high specificity. We have found that a combination of parylene biopatteming and polydimethylsiloxane (PDMS) microfluidics is a convenient means to immobilized multiple biomolecules in close proximity without cross-contamination as shown in Fig. 16.8. Parylene biopatteming is first used to expose only the regions of highest optical intensity of the nanosensor for functionalization. Second, a set of PDMS microfluidics is applied to the parylene-pattemed nanophotonic sensor, and the biomolecules to be attached... 

J. Steinbrink, M. Kohl, H. Obrig, G. Curio, F. Syre, F. Thomas, H. Wabnitz, H. Rinneberg, and A. Villringer. Somatosensory evoked fast optical intensity changes detected non-invasively in the adult human head. Neuroscience Letters, 291 105-108, 2000. 

Hinkle, Orr, and DallaValle (H11) passed a flat aerosol jet between two cylindrical electrodes, with the electrodes parallel to each other and to the plane of the aerosol jet. The jet was caused to spread toward the electrodes and was photographed. From the lateral displacement and optical intensity, they were able to obtain a distribution between positive, negative, and neutral particles and an approximate value of average charge. 

Up to now, we have given a general theoretical development of the self-beat technique. As a practical illustration of the experimental apparatus used to detect autocorrelation functions in scattering experiments, the equipment currently used in our laboratory will now be described. While our treatment of the autocorrelation function has been in terms of an analog signal, the computer that measures this function is actually a digital device. This is based on the fact that it is also valid to count the scattered photons in order to calculate Ci(r) as the optical intensity signal is essentially determined by the number of photons that strike the photocathode per unit time. We have then... 

Dynamic processes at thermodynamic equilibrium that occur within a time range from sub-microseconds to seconds can be probed without the imposition of a transient disturbance by optical intensity fluctuation spectroscopy. As such, dynamic light scattering (DLS) [155] measures the fluctuation of quasielastic scattering intensity and fluorescence correlation spectroscopy (FCS) [156-158] measures concentration fluctuations of specific fluorescent molecules... 

Figure 10 Diffraction efficiency of photorefractive grating as a function of optical intensity for composites containing either 3 or 5/NI. The composite containing 3 saturates at higher diffraction efficiencies than the composite containing 5/NI.

The time-resolved photoconductivity measurements shown in Fig. 15 give further support for a difference in the photoinduced charge transport in the polymerized samples versus the unpolymerized samples. For the incident laser of 100 mW/cm2 and a spot size of 2.5 mm, the decay time of the photoconductivity for the unpolymerized samples is 7.4 sec, whereas the photoconductivity of the polymerized samples does not significantly drop over a 30 sec period. Also, the photoconductivity of the polymerized sample is nearly twice that of the unpolymerized samples even at the peak of the unpolymerized photoconductive response. The unnormalized values for the dark conductivity in both samples is 1.7 x 10-10 S cm-1. The photoconductivity is 5.8 x 10-11 S cm-1 for the unpolymerized sample and 1.1 x 10-10 S cm-1 for the PSLC at an optical intensity of 2 W cm-2. 

The absorption cell is a glass silicon glass sandwich component (15xlx 0.4 mm) where optical intensities from different colored LEDs are measured by a 64 pixel CCD detector, see also Fig. 25. A demonstrator system with a total system volume of about 50 ml is illustrated in Fig. 26. 

The challenges outlined above still await a solution. In this section, we show how some of the theoretical limitations employed in traditional formulations of the band shape analysis can be lifted. We discuss two extensions of the present-day band shape analysis. First, the two-state model of CT transitions is applied to build the Franck-Condon optical envelopes. Second, the restriction of only two electronic states is lifted within the band shape analysis of polarizable chromophores that takes higher lying excited states into account through the solute dipolar polarizability. Finally, we show how a hybrid model incorporating the electronic delocalization and chromophore s polarizability effects can be successfully applied to the calculation of steady-state optical band shapes of the optical dye coumarin 153 (C153). We first start with a general theory and outline the connection between optical intensities and the ET matrix element and transition dipole. 

Hecht et al. (1992) published the ROA spectra of pinanes and pinenes. They reported the SCP and ICP Raman optical intensities for right angle scattering in the four naturally occuring substances. The intensities for both experimental techniques in each case were identical within the noise level of the experiments, well in agreement with theory for far from resonance conditions. 

In most cases an external electric field is applied across the material with the result that the mobile carrier distribution will experience drift in the field toward a new position. Even in the absence of an applied field, the nonuniform distribution of the mobile charge carriers created will lead to their relocation due to diffusion. Although the free carriers are generated where the optical intensity is high, their recombination with counterions (in the case of hole transport these are anions) may occur anywhere in the medium. This includes recombination where the intensity is low, resulting in the separation of the charge distributions. Subsequent optical excitation is unlikely in these darker regions. We know that the counterions exist in... 

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