A diode pumped doubling system employs a pump diode (2), a crystal (1) and doubler (8) in a laser cavity with the diode and is operated in a pulsed or low duty cycle pumping regimen, while the cavity length is sufficiently short to stabilize the transient responses to pulsed diode operation and produce stable and known or controlled energy output under the non-CW pumping regimen. The construction allows stable output to be maintained with much looser temperature control, and to be achieved during the initial turn-on interval of the laser diode. In a preferred embodiment, the device employs a doubler which is clamped across its non-critical axis, and is operated with a control system which creates isotherms in the active mode volume. The controller operates one or more separate heat sources and/or sinks to preheat the diode source (2) or doubling crystal (8) to maintain an oriented thermal gradient, and the rate or direction at which the isotherm migrates across the mode volume is controlled in accordance with the forthcoming pulse sequence to maintain effectively stable conditions during laser operation. The thermal control system may include sink (46), heater (42, 44) and control elements for pre-heating the laser diode before actuation, and during quiet intervals.