cotton-pickin Pulse Picker

Winfield Hill · 2016-06-05T19:31:35+00:00

Some reading for a lazy Sunday afternoon. A typical femto-second laser might give 65kW 0.1ps light pulses at a rate of 80MHz. But some applications can't handle a powerful light pulse every 12.5ns, for example fluorescence-lifetime measurements (we don't want to re-excite any molecules before achieving 100% decay). The solution is to add a light modulator, and run it from a pulse-picker. The picker should have adjustable pulse width and delay or phase, to exactly enable the modulator in the middle of a selected pulse. Pulse picker synchronizers typically cost $6000, but I figured it shouldn't be hard to design and make them for say, under $100. Here's my recently-completed RIS-761 divide-by-N pulse picker. It combines fast logic gates with a few analog-circuit functions to provide synchronization and shaping. In practice the phase and width settings would only be made once per laser setup, so knobs are not provided. The delay / phase is adjustable over a 20ns range, more than needed, and the width from 5 to 18ns. The 99cm pcb slides into a Hammond 2x4x4-inch extruded box, which is the most expensive component. Parson my poor cell-phone photo quality. -- Thanks, - Win

Jun 05, 2016 23 Replies

Rate this thread:

krw 10 years ago

Sounds like a delta-I problem in the making. I do my best to drive the two subcircuits out of phase (I'm currently using LVC2G04s for clock re-drivers.

Vote

John Larkin 10 years ago

HDMI are interesting, too.

John Larkin Highland Technology, Inc lunatic fringe electronics

Vote

John Larkin 10 years ago

CMOS has a terrible positive delay TC, many ps per degree C per gate. In a circuit like yours, that could be mostly compensated out with an LM45 or something.

John Larkin Highland Technology, Inc lunatic fringe electronics

Vote

Phil Hobbs 10 years ago

I've used them as well--they're nearly interchangeable, but HDMI has no latch, so it's liable to vibrate loose unless you tie it down somehow. Displayport is especially nice that way.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net

Vote

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required