Understanding Lasers: Chapter 7 Quiz
Source: Jeff Hecht, Understanding Lasers: An Entry-Level Guide, fourth edition (2019), Chapter 7 quiz, printed pages 249–251. The questions are paraphrased.
Quick answers
Question |
Answer |
|---|---|
1 |
b in the printed key; c is also false |
2 |
b, helium–cadmium |
3 |
d, argon fluoride |
4 |
a, approximately \(150\)–\(1500\ \mathrm{nm}\) |
5 |
c |
6 |
b, \(488.0\) and \(514.5\ \mathrm{nm}\) |
7 |
d |
8 |
e |
9 |
e, all listed discharge geometries |
10 |
a, carbon dioxide |
11 |
a |
12 |
b, HF |
Worked reasoning
Brief solution
1. Reasoning and answer.
General gas-laser statement: b in the key, but the item is ambiguous. Metal-vapour lasers use material that must be heated because it is not gaseous at room temperature, so b is false. However, c is also false: mixtures such as helium–neon deliberately contain a second species that transfers excitation energy. The item therefore has two defensible answers.
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General gas-laser statement: b in the key, but the item is ambiguous. Metal-vapour lasers use material that must be heated because it is not gaseous at room temperature, so b is false. However, c is also false: mixtures such as helium–neon deliberately contain a second species that transfers excitation energy. The item therefore has two defensible answers.
Brief solution
1. Reasoning and answer.
Shortest continuous-wave output: b. A helium–cadmium laser can emit continuously in the ultraviolet. The shorter-wavelength nitrogen and ArF choices normally operate as pulsed lasers.
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Shortest continuous-wave output: b. A helium–cadmium laser can emit continuously in the ultraviolet. The shorter-wavelength nitrogen and ArF choices normally operate as pulsed lasers.
Brief solution
1. Reasoning and answer.
Shortest wavelength overall: d. ArF excimer emission near \(193\ \mathrm{nm}\) is shorter than KrF, nitrogen, He–Cd, or argon-ion output in the choices.
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Shortest wavelength overall: d. ArF excimer emission near \(193\ \mathrm{nm}\) is shorter than KrF, nitrogen, He–Cd, or argon-ion output in the choices.
Brief solution
1. Reasoning and answer.
Electronic-transition span: a. Atomic and ionic gas-laser electronic transitions extend approximately from the deep ultraviolet near \(150\ \mathrm{nm}\) to the near infrared near \(1500\ \mathrm{nm}\). Molecular vibrational transitions extend much farther into the infrared but are not electronic transitions.
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Electronic-transition span: a. Atomic and ionic gas-laser electronic transitions extend approximately from the deep ultraviolet near \(150\ \mathrm{nm}\) to the near infrared near \(1500\ \mathrm{nm}\). Molecular vibrational transitions extend much farther into the infrared but are not electronic transitions.
Brief solution
1. Reasoning and answer.
Why retain a red He–Ne laser: c. It offers excellent spatial mode and beam quality. Diode lasers are generally smaller, cheaper, and more efficient.
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Why retain a red He–Ne laser: c. It offers excellent spatial mode and beam quality. Diode lasers are generally smaller, cheaper, and more efficient.
Brief solution
1. Reasoning and answer.
Strong argon-ion lines: b. The familiar blue and green lines are \(488.0\ \mathrm{nm}\) and \(514.5\ \mathrm{nm}\).
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Strong argon-ion lines: b. The familiar blue and green lines are \(488.0\ \mathrm{nm}\) and \(514.5\ \mathrm{nm}\).
Brief solution
1. Reasoning and answer.
After ignition of an argon discharge: d. High voltage initiates ionization; after breakdown, the voltage drops while a large current sustains the plasma and laser emission.
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After ignition of an argon discharge: d. High voltage initiates ionization; after breakdown, the voltage drops while a large current sustains the plasma and laser emission.
Brief solution
1. Reasoning and answer.
Helium–cadmium distinction: e. Cadmium must be heated to supply metal vapour. Neon is already gaseous under the tube’s operating conditions.
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Helium–cadmium distinction: e. Cadmium must be heated to supply metal vapour. Neon is already gaseous under the tube’s operating conditions.
Brief solution
1. Reasoning and answer.
CO2 excitation geometries: e. CO2 lasers have been built with longitudinal, transverse, high-pressure, and flowing-gas discharges.
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CO2 excitation geometries: e. CO2 lasers have been built with longitudinal, transverse, high-pressure, and flowing-gas discharges.
Brief solution
1. Reasoning and answer.
Highest industrial gas-laser power: a. Carbon-dioxide lasers scale to high continuous power and have long been major cutting and welding tools.
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Highest industrial gas-laser power: a. Carbon-dioxide lasers scale to high continuous power and have long been major cutting and welding tools.
Brief solution
1. Reasoning and answer.
Excimer lower level: a. The excited dimer is bound, but its ground state is repulsive. After photon emission it promptly dissociates, helping keep the lower laser level empty.
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Excimer lower level: a. The excited dimer is bound, but its ground state is repulsive. After photon emission it promptly dissociates, helping keep the lower laser level empty.
Brief solution
1. Reasoning and answer.
Not an excimer molecule: b. ArF, KrF, XeCl, and XeF are excimer or exciplex laser species. HF is the molecule in a chemical laser.
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Not an excimer molecule: b. ArF, KrF, XeCl, and XeF are excimer or exciplex laser species. HF is the molecule in a chemical laser.