yeah i know "pure" sounds a crazy word, actually i wanted to have 50 nanosecond pulse width with 1KHz PRF. i wanted to build a TTL level signal. i tried many circuits but i failed. the laser the rise/fall time the better it will look like pulse.
The normal 74xx123 monostables struggle to get down to 50ns. I have generated 25ns and 50ns pulses with microcontrollers but that is overkill if you don't need one anyway. Your best bet may be to use a fast comparator with push-pull output (i.e. not open collector/drain). Look at the TLV3501 from Texas Instruments for example.
How about using the transition delay of gates to generate your pulse, TTL = 10nS/gate. Input pulse via 5 Nand gates into an output nand gate with the input pulse on the other input. If too short add a bit of capacitance o one of the series inputs.
Frank