Understanding Lasers: Chapter 11 Quiz

Source: Jeff Hecht, Understanding Lasers: An Entry-Level Guide, fourth edition (2019), Chapter 11 quiz, printed pages 421–423. The questions are paraphrased.

Quick answers

Question

Answer

1

a

2

e, about 20–40 nm

3

e

4

e, about \(5.85\ \mathrm{\mu m}\)

5

b, signal wavelength

6

c, optical parametric amplifier

7

d, laser-produced tin plasma

8

a

9

d, all listed bands

10

a

Worked reasoning

  1. Dye tunability: a. Each electronic state has many closely spaced molecular vibrational sublevels, producing a broad gain band from which a cavity can select different wavelengths.

  2. Typical single-dye tuning span: e. An individual dye commonly covers a few tens of nanometres; changing dyes extends the total accessible range.

  3. Dye-laser linewidth: e. The broad dye gain does not uniquely set output linewidth. Cavity length, gratings, etalons, and other selection optics do.

  4. OPA idler wavelength: e. Parametric energy conservation is

    \[\nu_p=\nu_s+\nu_i,\]

    so

    \[\frac1{\lambda_i}=\frac1{1064\ \mathrm{nm}} -\frac1{1300\ \mathrm{nm}},\qquad \lambda_i=5.85\times10^3\ \mathrm{nm}\approx5.85\ \mathrm{\mu m}.\]

  5. OPO tuning reference: b. The resonator normally selects and tunes the signal wave; the idler then follows from energy conservation with the pump.

  6. Broadest tuning source: c. An optical parametric amplifier has no resonant signal cavity restricting its range and can cover an exceptionally broad span through phase matching.

  7. Shorter-than-193-nm lithography source: d. Extreme-ultraviolet systems use droplets of tin vaporized into plasma by high-power CO2-laser pulses.

  8. Free-electron-laser emitter: a. A relativistic electron beam oscillates through the alternating magnetic field of an undulator and radiates.

  9. FEL spectral bands: d. By changing electron energy and undulator parameters, FELs can operate from infrared through ultraviolet to X-rays.

  10. Energy extraction: a. The periodic magnetic field bends the electron trajectories. Their radiation interacts coherently with the bunched beam, transferring electron kinetic energy into light.