Understanding Lasers: Chapter 13 Quiz
Source: Jeff Hecht, Understanding Lasers: An Entry-Level Guide, fourth edition (2019), Chapter 13 quiz, printed pages 512–514. The questions are paraphrased.
Quick answers
Question |
Answer |
|---|---|
1 |
d |
2 |
c |
3 |
b, \(80\ \mathrm J\) under the key’s assumption |
4 |
a, diamond drilling |
5 |
a, cutting |
6 |
e, all listed uses |
7 |
b, excimer lasers |
8 |
d, dark hair and light skin |
9 |
b, excimer lasers |
10 |
d, diode-pumped solid-state and fibre lasers |
11 |
e, all listed targets |
12 |
e, the retina |
Worked reasoning
Brief solution
1. Reasoning and answer.
Not an attraction of high-power lasers: d. Lasers can deliver intense, localized, noncontact energy under robotic control. Burning chemical fuel is not an intrinsic advantage of the tool.
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Not an attraction of high-power lasers: d. Lasers can deliver intense, localized, noncontact energy under robotic control. Burning chemical fuel is not an intrinsic advantage of the tool.
Brief solution
1. Reasoning and answer.
Baby-bottle nipple drilling: c. A mechanical drill would deform the soft elastomer. A laser applies energy without contact force and can make a repeatable small opening.
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Baby-bottle nipple drilling: c. A mechanical drill would deform the soft elastomer. A laser applies energy without contact force and can make a repeatable small opening.
Brief solution
1. Reasoning and answer.
Titanium energy absorption: b only with an unstated assumption. Energy delivered in one second is
2. Key calculation.
\[E_{\mathrm{absorbed}}=A Pt=(0.08)(1000)(1)=80\ \mathrm J.\]Show detailed steps
Titanium energy absorption: b only with an unstated assumption. Energy delivered in one second is
\[E_{\mathrm{incident}}=Pt=(1000\ \mathrm W)(1\ \mathrm s)=1000\ \mathrm J.\]The printed key’s \(80\ \mathrm J\) result assumes absorptance \(A=0.08\):
\[E_{\mathrm{absorbed}}=A Pt=(0.08)(1000)(1)=80\ \mathrm J.\]Important
Missing data
The question as printed does not state the titanium absorptance or point to a table containing it. Without \(A\), the absorbed energy is underdetermined; only the incident \(1000\ \mathrm J\) is known.
Brief solution
1. Reasoning and answer.
Most concentrated peak power: a. Diamond drilling must remove an exceptionally hard, high-temperature material in a tiny region, demanding higher localized peak intensity than the surface-treatment choices.
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Most concentrated peak power: a. Diamond drilling must remove an exceptionally hard, high-temperature material in a tiny region, demanding higher localized peak intensity than the surface-treatment choices.
Brief solution
1. Reasoning and answer.
Gas-jet-assisted process: a. Cutting jets eject molten material from the kerf; oxygen can also add exothermic heating for suitable metals.
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Gas-jet-assisted process: a. Cutting jets eject molten material from the kerf; oxygen can also add exothermic heating for suitable metals.
Brief solution
1. Reasoning and answer.
Additive manufacturing: e. It spans hobby parts, rapid prototypes, otherwise unmanufacturable geometries, and economical small production runs such as replacement aircraft components.
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Additive manufacturing: e. It spans hobby parts, rapid prototypes, otherwise unmanufacturable geometries, and economical small production runs such as replacement aircraft components.
Brief solution
1. Reasoning and answer.
Semiconductor photolithography: b. Deep-ultraviolet KrF and ArF excimer lasers provide the short wavelengths used by major lithography generations.
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Semiconductor photolithography: b. Deep-ultraviolet KrF and ArF excimer lasers provide the short wavelengths used by major lithography generations.
Brief solution
1. Reasoning and answer.
Best hair-removal contrast: d. Dark melanin-rich hair absorbs strongly while light skin absorbs less, maximizing selective follicle heating and reducing skin damage.
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Best hair-removal contrast: d. Dark melanin-rich hair absorbs strongly while light skin absorbs less, maximizing selective follicle heating and reducing skin damage.
Brief solution
1. Reasoning and answer.
LASIK source: b. An ArF excimer laser near \(193\ \mathrm{nm}\) photoablates corneal tissue with shallow penetration and precise removal.
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LASIK source: b. An ArF excimer laser near \(193\ \mathrm{nm}\) photoablates corneal tissue with shallow penetration and precise removal.
Brief solution
1. Reasoning and answer.
Current weapon-development source: d. Modern programmes emphasize electrically powered diode-pumped bulk and fibre lasers rather than the large hazardous chemical-laser systems explored historically.
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Current weapon-development source: d. Modern programmes emphasize electrically powered diode-pumped bulk and fibre lasers rather than the large hazardous chemical-laser systems explored historically.
Brief solution
1. Reasoning and answer.
Envisioned targets: e. Proposed defensive systems include rockets, artillery or mortar projectiles, drones, and small boats.
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Envisioned targets: e. Proposed defensive systems include rockets, artillery or mortar projectiles, drones, and small boats.
Brief solution
1. Reasoning and answer.
Most vulnerable target: e. The eye focuses incoming light onto the retina, multiplying irradiance dramatically; far less incident energy can injure it than is needed to disable robust hardware.
Show detailed steps
Most vulnerable target: e. The eye focuses incoming light onto the retina, multiplying irradiance dramatically; far less incident energy can injure it than is needed to disable robust hardware.