Understanding Lasers: Chapter 8 Quiz

Source: Jeff Hecht, Understanding Lasers: An Entry-Level Guide, fourth edition (2019), Chapter 8 quiz, printed pages 297–299. The questions are paraphrased.

Quick answers

Question

Answer

1

c, GaAs diode laser

2

b, flashlamp

3

a, 808-nm diode

4

c, chlorine

5

e

6

d, ytterbium

7

a

8

b, \(347\ \mathrm{nm}\)

9

c, \(477\ \mathrm{nm}\)

10

a, titanium–sapphire

11

d

12

e, erbium

13

d, OPSL/VECSEL

14

b, titanium–sapphire

Worked reasoning

  1. Not in the conventional solid-state category: c. This book treats electrically injected semiconductor diode lasers separately from lasers whose dopant ions are embedded in a dielectric solid host.

  2. Best listed general pump: b. A flashlamp supplies intense broadband light overlapping absorption bands; a properly wavelength-matched diode would usually be better, but none is offered in this item.

  3. Best neodymium pump: a. An \(808\ \mathrm{nm}\) diode overlaps a strong Nd absorption band, giving efficient, selective pumping.

  4. Not an active ion: c. Neodymium, titanium, chromium, and ytterbium are established solid-state laser dopants; chlorine is not one of the active species described.

  5. Glass-host advantage: e. Glass is readily fabricated in large rods, slabs, and fibres, although its thermal conductivity is generally poorer than that of crystalline hosts.

  6. Quasi-three-level system: d. Ytterbium’s lower laser level is close enough to the ground state to be thermally populated, so reabsorption must be overcome.

  7. Thin-disk pumping: a. Diode light enters through the broad disk face, often making multiple passes, while the thin geometry efficiently removes heat through the back surface.

  8. Ruby second harmonic: b.

    \[\lambda_2=\frac{694\ \mathrm{nm}}2=347\ \mathrm{nm}.\]

  9. Not a ready Nd:YAG harmonic: c. Nd:YAG directly gives \(1064\ \mathrm{nm}\); doubling, tripling, and quadrupling give about 532, 355, and \(266\ \mathrm{nm}\). The listed \(477\ \mathrm{nm}\) value is not one of those harmonics.

  10. Broadest solid-state gain band: a. Titanium–sapphire couples its electronic transition to lattice vibrations and supports a very broad emission band.

  11. Vibronic distinction: d. Strong interaction between electronic and vibrational states broadens gain, enabling wide tunability and short pulses.

  12. Least retinal hazard: e. Erbium lasers around \(3\ \mathrm{\mu m}\) are strongly absorbed by water in the cornea and do not focus onto the retina as visible and near-infrared beams do. They remain hazardous to the eye surface.

  13. Compact separate visible colours: d. Optically pumped semiconductor lasers, also called VECSELs, can be engineered and frequency converted for multiple visible wavelengths.

  14. Femtosecond source: b. Titanium–sapphire’s broad gain bandwidth supports mode-locked pulses lasting only femtoseconds.