We measured the gain and the spatial temperature distribution of the first four amplifier stages among the five-stage Nd : glass rod amplifer system in our laboratory. Diameters of the amplifier rods are 16mm, 30mm, 40mm, 64mm, and 90mm, and the lengths of them were 360mm. We used the Quantronics Model #4216 Nd : YLF laser as a master oscillator. When delay times between Q-switched - mode locked pulse and flashlamp trigger pulse were between 400 μ $\sec$ and 450 μsec, the gains had maximum. The maximum gains were 55, 12, 8.5, and 4.0 for the first, the second, the third, and the fourth stage at the flashlamp input energy 15kJ. The numbers of Xe-flashlamp used in each stage were 4, 4, 12, and 12, respectively. The electronic circuit for the flashlamps had a Pulse Forming Network(PFN) having 100 μF capacitor and 100 μH inductor for each flashlamp. With this PFN, flashlamp pulse width was 400 μ $\sec$. By the thermal birefringence measurement, it was hown that the temperature differences between the center and the circumference were less than 0.3℃ within 1 second after flashlamp pumping. After one minute from the flashlamp pumping, it became less than 0.2℃. After two minute from the pumping, it became less than 0.15℃. The periods for the thermal birefringence effect to disappear were different for each stage and those maximum time was less than 15-minute.
