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
-------------

.. csv-table::
   :header: "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**, :math:`347\ \mathrm{nm}`"
   "9", "**c**, :math:`477\ \mathrm{nm}`"
   "10", "**a**, titanium--sapphire"
   "11", "**d**"
   "12", "**e**, erbium"
   "13", "**d**, OPSL/VECSEL"
   "14", "**b**, titanium--sapphire"

Worked reasoning
----------------

#. **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.

#. **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.

#. **Best neodymium pump: a.**  An :math:`808\ \mathrm{nm}` diode overlaps a
   strong Nd absorption band, giving efficient, selective pumping.

#. **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.

#. **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.

#. **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.

#. **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.

#. **Ruby second harmonic: b.**

   .. math::

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

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

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

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

#. **Least retinal hazard: e.**  Erbium lasers around
   :math:`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.

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

#. **Femtosecond source: b.**  Titanium--sapphire's broad gain bandwidth
   supports mode-locked pulses lasting only femtoseconds.