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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Gas-jet-assisted process: a. Cutting jets eject molten material from the kerf; oxygen can also add exothermic heating for suitable metals.

  6. Additive manufacturing: e. It spans hobby parts, rapid prototypes, otherwise unmanufacturable geometries, and economical small production runs such as replacement aircraft components.

  7. Semiconductor photolithography: b. Deep-ultraviolet KrF and ArF excimer lasers provide the short wavelengths used by major lithography generations.

  8. Best hair-removal contrast: d. Dark melanin-rich hair absorbs strongly while light skin absorbs less, maximizing selective follicle heating and reducing skin damage.

  9. LASIK source: b. An ArF excimer laser near \(193\ \mathrm{nm}\) photoablates corneal tissue with shallow penetration and precise removal.

  10. 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.

  11. Envisioned targets: e. Proposed defensive systems include rockets, artillery or mortar projectiles, drones, and small boats.

  12. 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.