Problem 4
Assume a semiconductor laser has a length of \(800 \mu \mathrm{m}\). Laser emission can occur when the cavity length is equal to an integer number of half wavelengths. What wavelengths in the range \(650 \mathrm{nm}<\lambda<\) \(652 \mathrm{nm}\) can this laser emit, and in each case, list the cavity length in wavelengths.
Problem 5
Assume two energy levels of a gas laser are separated by \(1.4 \mathrm{eV},\) and assume that they are equally degenerate \(\left(g_{1}=g_{2}\right)\). The spontaneous emission Einstein coefficient for transitions between these energy levels is given by \(A_{12}=3 \cdot 10^{6} \mathrm{~s}^{-1}\). Find the other two Einstein coefficients, \(B_{12}\) and \(B_{21}\).
Problem 6
The energy gap of AlAs is \(2.3 \mathrm{eV},\) and the energy gap of \(\mathrm{AlSb}\) is 1.7 eV \([9,\) p. 19\(]\). Energy gaps of materials of composition \(A l A s_{x} S b_{1-x}\) with \(0 \leq x \leq 1\) vary approximately linearly between these values \([9, \mathrm{p} .19]\). Suppose you would like to make a semiconductor laser from a material of composition AlAs \(_{x} \mathrm{Sb}_{1-x}\). Find the value of \(x\) that specifies the composition of a material which emits light at wavelength \(\lambda=640 \mathrm{nm}\)
Problem 10
Three main components of a laser are the pump, active material, and cavity. Four main types of lasers are gas lasers, semiconductor lasers, dye lasers, and solid state lasers. Match the example component with the best description of the type of component and type of laser it is found in specified. (Each answer will be used once.) $$ \begin{array}{|l|} \hline \text { Example Component } \\ \hline \text { 1. Edges of a AlGaAs crystal } \\ \hline \text { 2. Rhodamine } 6 \text { G liquid solution } \\ \hline \text { 3. External mirror made of } \mathrm{SiO}_{2} \text { glass coated with } \\ \text { aluminum } \\ \hline \text { 4. Battery of a laser pointer } \\ \hline \text { 5. } \mathrm{SiO}_{2} \text { glass doped with } 1 \% \text { Er atoms } \\ \hline \text { 6. } \mathrm{CO}_{2} \text { gas in an enclosed tube } \\ \hline \text { 7. Pn junction made from InGaAs } \\ \hline \text { 8. Argon ion laser used to supply energy to excite } \\ \text { electrons of a Ti doped Sapphire } \\ \hline \hline \text { Description } \\ \hline \hline \text { A. Cavity of a semiconductor laser } \\ \hline \text { B. Cavity of a gas laser } \\ \hline \text { C. Active material of a semiconductor laser } \\ \hline \text { D. Active material of a gas laser } \\ \hline \text { E. Active material of a dye laser } \\ \hline \text { F. Active material of a solid state laser } \\ \hline \text { G. Pump of a semiconductor laser } \\ \hline \text { H. Pump of a solid state laser } \\ \hline \end{array} $$
Problem 11
The intensity from sunlight on a bright sunny day is around \(0.1 \frac{\mathrm{W}}{\mathrm{cm}^{2}}\). Laser power can be confined to a very small spot size. Assume a laser produces a beam with spot size \(1 \mathrm{~mm}^{2}\). For what laser power in watts will the intensity of the beam be equivalent to the intensity from sunlight on sunny day? Staring at the sun can damage an eye, so staring at a laser beam of this intensity is dangerous for the same reason.
