Photodiode response

Indirect Observation of Deformation Bands. Although birefringence results shown in the various plots to this point imply a smoothly increasing value of the intensity, I, such was not always the case. An interesting and entirely unexpected behavior was observed in the response of many specimens. In some cases, though not in all, this phenomenon occurred only when the laser beam traversed the sample at the subsequent fracture point. A typical example, in which the relative photodiode response (see Equation 1) is plotted as a function of time, is seen in Figure... 

Figure 9. Recorder output of relative photodiode response as a function of time for a birefringence experiment on PMMA containing 2.2% HiO at a strain rate of...

Figure 21. Oscilloscope picture showing photodiode response (change in optical transmittivity of the cell) to triangular pulses of opposite polarity (4 V peak-to-peak), demonstrating threshold, saturation, memory, and symmetry bistability cf. Fig. 11. The material is DOBAMBC at 60 X. Horizontal scale 1.5 V/div (from [95]).

Figure 15-12. Spectrally resolved pliotocurrent of a ITO/PPV/Mg photodiode at dilTcrcnt bias after correction for dark current, light source, and monochromator response, and normalization to the same peak value. The broken line is the normalized absorption spectrum of PPV (reproduced by permission of the Institute of Physics from Ref. 143)).

Kigurc 15-22. Spectral response of die photocurrcnl in ITO/MEH-PFV/Qj/Au photodiode al (reverse) -1 V bias (reproduced by pennission of llie American Insti-lule of Physics from Rel. [89J). 

Electrochemical detection is sensitive and selective, and it gives useful information about polyphenolic compounds in addition to spectra obtained by photodiode array detectors. Differences in electrochemically active substituents on analogous structures can lead to characteristic differences in their voltammetric behavior. Because the response profile across several cell potentials is representative of the voltammetric properties of a compound, useful qualitative information can be obtained using electrochemical detection (Aaby and others 2004). 

A medically reliable UV sensor should have a spectral responsivity that closely follows the erythemal curve between 390 nm and 290 nm. So far, a photodiode with this specific sensitivity has not been available. Modeling the erythema spectrum with the help of filters also delivered only poor results. In fact, most available sunburn detectors vary in their spectral responsivity and may therefore only be used as an indicator for the actual UV charge. 

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