Download Exam 2 - Light Matter Interaction - Summer 2002 | OSE 5312 and more Exams Chemistry in PDF only on Docsity! OSE 5312 OPTICAL PROPERTIES OF MATERIALS Summer 2002 Exam 2: Monday, July 15, 10 am – noon This is a closed book, closed notes exam. However, you are allowed a single 8 ½ ” x 11” sheet of paper with handwritten notes. Answer all questions. Start each question on a new sheet. Write on one side of the paper only and number each sheet and write your name on it. Pay attention to the maximum credit for each question. 1. A 7 cm long laser rod with small signal gain 0 = 0.02 cm-1 and saturation intensity Isat = 100 W/cm2 has antireflection coatings on its ends so that the transmittance of each end of the rod is 99.3 %. The rod is placed in a laser cavity with a 95 % reflectance output coupler and a 99.5 % reflectance end mirror. There are no other elements in the cavity and no absorption or scattering losses. We may therefore make the “high-Q approximation” in estimating laser cavity output power. (a) If the laser gain medium is homogeneously broadened, what is the output irradiance of the laser? (10 points) (b) If the laser gain medium is inhomogeneously broadened but the vaues of 0, Isat, etc. remain the same, derive an expression for the laser output irradiance. (10 points) (c) Using your derived expression, calculate the output irradiance of the inhomogeneously broadened laser. (5 points) 2. Explain the main differences between 3-level lasers that use the lower two levels for the laser transitions and 4-level lasers. Your answer should include: (a) detailed diagrams showing the important rates. (b) a description of which rates should be large, which small, including some comments as to why. (c) a comment on which of these level systems is best suited to c.w. operation. (total points for Q2: 20) 3. A Nd:Glass laser transition has center wavelength 1054 nm and a FWHM (full-width at half maximum) transition width of 2 nm. (a) If this laser is to be mode locked, approximately how short of a pulse can be generated? (10 points) (b) If the laser cavity is 0.5 m long, approximately how many longitudinal modes will run if the laser is mode locked to produce the shortest possible pulse? You may assume that the length of the rod is negligible small compared to the rest of the cavity for this
