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Chapter 7: Q 7.20 (page 194)

Describe the basis for radiation detection with a silicon photodiode transducer.

Short Answer

Expert verified

A silicon photodiode transducer is a p-n junction device operated under reverse biased conditions.

Step by step solution

01

Given information.

Describe the basis for radiation detection with a silicon photodiode transducer.

02

Explanation.

A silicon photodiode transducer consists of a reverse-biased pn-junction formed on a silicon chip. The reverse bias creates a depletion layer that reduces the conductance of the junction to nearly zero as shown in figure below. If radiation impinges on the chip, however, holes and electrons are formed in the depletion layer and attracted to the appropriate electrode to produce a current that is proportional to radiant power. They require only low-voltage power supplies or can be operated under zero bias. Because of this, they are widely used in portable, battery powered instruments.

A schematic diagram of a silicon diode is as under.

The formation of depletion layer, which prevents flow of electricity under reverse bias is as

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Most popular questions from this chapter

The Wien displacement law states that the wavelength maximum in micrometers for blackbody radiation is

given by the relationship

$λ_{m a x} T = 2.90 \times 10^{3}$

where T is the temperature in kelvins. Calculate the wavelength maximum for a blackbody that has been

heated to (a) 4500 K, (b) 2500 K, and (c) 1250 K.

Define the term effective bandwidth of a filter.

The behavior of holographic filters and gratings is described by coupled wave theory. The Bragg wavelength $λ_{b}$ for a holographic optical element is given by

$λ_{b} = 2 n d \cos θ$

where $n$ is the refractive index of the grating material; $d$ is the grating period, or spacing; and $θ$ is the angle of incidence of the beam of radiation.

( $a$ ) Create a spreadsheet to calculate the Bragg wavelength for a holographic grating with a grating spacing of $17.1 μm$ and a refractive index of $1.53$ at angles of incidence from $0$ to $90 °$ .

( $b$ ) At what angle is the Bragg wavelength $462 n m$ ?

( $c$ ) The Bragg wavelength is sometimes called the “playback wavelength.” Why?

( $d$ ) What is the historical significance of the term “Bragg wavelength?”

( $e$ ) A tunable volume holographic filter has been developed for communications applications. The filter is said to be tunable over the wavelength range $2 n d$ to $2 d \sqrt{n^{2} - 1}$ . If the filter has a Bragg wavelength of $1550 n m$ and a grating spacing of $535 nm$ , calculate the angular tuning range of the filter.

( $f$ ) Find the Bragg wavelength for a grating with a spacing of $211.5 n m$ , assuming that the grating is made of the same material. Find the wavelength range over which this grating may be tuned.

( $g$ ) Discuss potential spectroscopic applications of tunable holographic filters.

( $h$ ) When a volume grating is created in a holographic film, the refractive index of the film material is varied by an amount $∆ n$ , which is referred to as the refractive-index modulation. In the ideal case, this quantity is given by

$Δ n \approx \frac{λ}{2 t}$

where $λ$ is the wavelength of the laser forming the interference pattern, and $t$ is the thickness of the film. Calculate the refractive-index modulation in a film $38 μm$ thick with a laser wavelength of $633 nm$ .

( $i$ ) For real gratings, the refractive-index modulation is

$Δ n = \frac{λ \sin^{- 1} \sqrt{D_{e}}}{π t}$

where $D_{e}$ is the grating efficiency. Derive an expression for the ideal grating efficiency, and determine its value.

( $j$ ) Calculate the efficiency for a grating $7.5 μ m$ thick if its refractive-index modulation is $0.030$ at a wavelength of $633 n m$ .

( $k$ ) Holographic films for fabricating filters and gratings are available commercially, but they can be made in the laboratory using common chemicals. Use a search engine to find a recipe for dichromate gelatin for holographic films. Describe the fabrication of the films, the chemistry of the process, and how the films are recorded.

A monochromator with a focal length of $0.75 m$ was equipped with an echellette grating with $3000$ blazes per millimeter.

(a) Calculate the reciprocal linear dispersion of the instrument for first-order spectra.

(b) If localid="1646643497497" $2.0 cm$ of the grating were illuminated, what is the first-order resolving power of the monochromator?

(c) At approximatelylocalid="1646643508082" $400 nm$ , what minimum wavelength difference could in theory be completely resolved by the instrument?

With the aid of Figures 7-2 and 7-3, suggest instrument components and materials for constructing an instrument that would be well suited for

(a) the investigation of the fine structure of absorption bands in the region of 450 to 750 nm.

(b) obtaining absorption spectra in the far IR (20 to 50 μm).

(c) a portable device for determining the iron content of natural water based on the absorption of radiation by the red Fe(SCN)21 complex.

(d) the routine determination of nitrobenzene in air samples based on its absorption peak at 11.8 μm.

(e) determining the wavelengths of flame emission lines for metallic elements in the region from 200 to 780 nm.

(f) spectroscopic studies in the vacuum UV region.

(g) spectroscopic studies in the near IR.

See all solutions

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