Photodetectors

Bandwidth Mode Temp., Material Pixel size. Focal plane Principle Cutoff Response Responsivi D,  

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Detectors aie all intrinsic unless otherwise noted. See Fig. 1. Visible bandwidth near infrared = 0.700-1.00 fim. 

There are important figures of merit (5) that describe the performance of a photodetector. These are responsivity, noise, noise equivalent power, detectivity, and response time (2,6). However, there are several related parameters of measurement, eg, temperature of operation, bias power, spectral response, background photon flux, noise spectra, impedance, and linearity. Operational concerns include detector-element size, uniformity of response, array density, reflabiUty, cooling time, radiation tolerance, vibration and shock resistance, shelf life, availabiUty of arrays, and cost. 

Photodetectors exhibit well-defined, cutoff wavelength thresholds, the positions of which are determined by the magnitudes of the band gap activation energy, E, or impurity-activation energy, E. The cutoff wavelength, corresponds to a photochemical activation energy, E, where. 

---

When directed towards the test piece the laser beam passes through a centre hole in a 45 degree fixed-angle mimor. Between this mirror and the test piece the laser beam and the flourescence follow a common beam path. A photodetector is aimed at the 45 degrees angle mirror and, therefore, looks along the laser in this common beam path, see Fig 3. 

The principle of optical triangulation has been known since the time of the early Greeks, and indeed optical triangulation has been used for hundreds of years in applications such as surveying, camera auto-focus and even smart-bombs. With the advent of low-cost, compact electro-optic components such as lateral-effect photodetectors, diode lasers and micro-optics, laser-based triangulation sensors can now be employed for applications that were, heretofore, considered uninspectable. 

As a result of these considerations, the primary difference between a spectrophotometer and a light-scattering photometer is the fact that the photodetector is mounted on an arm which pivots at the sample so that intensity measurements can be made at various angles. 

Figure 10.9 Light-scattering photometers, (a) Schematic top view showing movable photodetector. (Reprinted from Ref. 2, p. 176.) (b) Cutaway photograph of commercial light-scattering instrument, the Brice-Phoenix Universal Scattering Photometer. (Photo courtesy of the Virtis Co., Gardiner, New York.)...

INFRARED TECHNOLOGY AND RAMAN SPECTROSCOPY - RAMAN SPECTROSCOPY] (Vol 14) -silicon photodetectors [PHOTODETECTORS] (Vol 18)... 

---