Measurement of Absorption Efficiency by a Leakage Power Analysis Method from an Efficient Nd:YAG Rod Laser Pumped by Diode Bars

We proposed a leakage power analysis method to measure the absorption efficiency of a diode side-pumped Nd:YAG rod laser which was fabricated using a 3-fold symmetric gold-coated flow tube. The pump power from the 3 diode bar modules was coupled into the reflector through AR-coated windows. A maximum output power of 150 W with a slope efficiency of 47% was obtained from a Nd:YAG rod of 4 mm diameter at the diode pump power of 434 W, which corresponds to an optical efficiency of 34.6%. We investigated the thermally induced lens and pump light distribution of the 4-mm and 6-mm rods. The high slope efficiency originated from the wing-pumping scheme, uniform pump light distribution and the high absorption efficiency. By fixing the wavelength of the diode at 802.4 nm, we measured the absorption efficiency, using the leakage power analysis method, which agreed well with the results obtained using the Findlay-Clay method. Therefore, the leakage power analysis method was demonstrated to be simpler and more reliable because it gives accurate values without the need to adjust diode wavelength. An absorption efficiency of 94% was measured for the case of a 4-mm rod.