Quiz 4 (Detectors)

Question 1

Single channel

Answer 1

measure photon intensity @ a single wavelength with respect to time

Question 2

Multichannel

Answer 2

measure photon intensity over a wide range of wavelengths simultaneously
(grating remains in fixed position)

Question 3

Vacuum phototube process

Answer 3

1. Bias cathode to -90V relative to anode
2. Photon hits cathode, photoelectron is emitted
3. Electron is collected @ anode

wavelength range: 200-1100nm

Question 4

Photomultiplier tube

Answer 4

1. Photon hits photocathode & emits electron
2. Electron is accelerated to dynode #1 to form 2 electrons
3. Electrons generated @ dynode #9 are collected @ anode (large current gain)
4. Current follower converts current to voltage

wavelength range: 200-1100nm

Question 5

Photodiode detector

Answer 5

1. Reverse bias P/N junction
2. Photon strikes depletion region
3. Electron is promoted from valence band to conduction band ( form hole/electron pair that are mobile)

wavelength range: 250-1100nm

Question 6

Multichannel advantages

Answer 6

1. fast ( no scanning)
2. rugged (no moving parts)
3. highly reproducible

Question 7

Charge Coupled Device

Answer 7

1. apply 10V to metallic electrode (generates depletion region)
2. Photon strikes depletion region —> form hole/electron pair —> collects electrons in the well
3. process continues over a set integration time
4. at end of process, “capacitor” is discharged and the current collected is proportional to the number of electrons collected in the well

wavelength range: 200-1100 nm

Question 8

CCD layout

Answer 8

metallic electrodes on top
insulator
potential well
p-type silicon

Question 9

Photomultiplier tube layout

Answer 9

photocathode at front
dyodes on bottom
anode at back
current follower at end

Question 10

Vacuum phototube layout

Answer 10

quartz or glass cylinder
anode & cathode opposite each other

Question 11

Detectors

Answer 11

transducers that convert light into electrical energy (current or voltage)