2. Experimental set-up of a Nd: YAG laser which is longitudinally pumped by a diode laser is shown below. The plot shows the output power of the YAG laser as a function of the electrical input power of the diode laser. a. What is the laser slope efficiency? b. What is the electrical input power threshold (Pm)? c. How many photons are in the cavity? Assume Am (mode area) is approximately equal to 0.5 x circular area of the YAG rod. NO YAG 95 diode coupling reflective mirror rod 10cm radius 6=2.8 x 10" cm array optics T = 230 us TE reflectivity of flat mirror =1 cooler plane TEMOO reflectivity of the curved mirror=0.95 light input mirror light output 0.805 - 0 808 um HR at 1 06um 106 pm distance between mirrors= 5.5 cm AR at 0 81 um AR at 106 pm YAG rod: 1 cm long, 0.4 cm diameter Refractive index of YAG = 1.82 electrical input power, W 0 03 1 19 28 3.8 400 1600 350 1400 Nd: YAG = 300 1200 E = 250 -1000 9 200 diode optical output power mw Nd : YAG , TEMoo mode, CW optical output power, mi GOALAS diode temp = 35 C 150 100 600 50 200 0 5 10 1-5 2-0 diode current, A (from Electron. Lett. 23, 669 (1987))