You can try PIC18F series from Microchip, should me available in India. It can run up to 40Mhz, it needs only 100ns / per instruction, should fit to your needs.
I believe it's called a Q-Switch in Laser systems. They are typically optically-based switches that are way faster than standard electronic circuits, and they are VERY expensive. If you intend to use a microprocessor for it, that would mean a 1GHz one. Quite impossible for a microcontroller. If you can afford a few ns, then you could use a monostable pulse generator. Refer to the 74HCT123. I vaguely remember generating pulses of below 10ns using this.