高輝度マイクロチップレーザーとエンジン点火

摘要

A passively Q-switched Nd:YAG/Cr:YAG microchip laser was developed. The output energy of 3 mJ per pulse (totally 12 mJ for 4 pulses) was obtained with the optical-to-optical efficiency of 19 %. The pulse width and M~2 value were 500 ps and 1.2, respectively. The brightness of the microchip laser was calculated to be 0.3 PW/sr-cm~2 and the optical power intensity of 5 TW/cm~2 was estimated at the focal point of ignition. A 100 %-ignition was successfully demonstrated by a five-pulse train in a lean mixture of an A/F 17.2, where spark plug ignition failed. Finally, ignition tests for a real automobile engine were performed. A single laser pulse with an energy of 2.3 mJ could ignite and drive the engine stably. It will be lowest energy ever reported for laser ignition of a real automobile engine. We can confirm that an optimally designed, high-brightness, passively Q-switched microchip laser reduced the ignition energy dramatically compared with previous ignition lasers and a spark plug and the dimension of the laser head can be reduced to real spark plug size.