You CAN jam police radar by emitting radio waves in direction of radar (front).
Laidar works the same way as radar, but instead of radio waves it uses light.
The principle is the same, laidar uses laser beem which bounces of car and returns at differen wavelength. Doppler effect.
Now, about IR LEDs. You don't need fast oscilator to drive LEDs. Mentioned wavelength of 920nm does have something to do with frequency, but not in that way. It means that wavelength of light is 920nm (372826086.957 Hz). It is just below visible frequency range.
Visit
http://www.sengpielaudio.com/calculator-wavelength.htm
You should probably use many more LED's since they're weak and because laser signal has all power directed at one spot, so you'll need more LEDs to overpower that signal.
If you do attempt to build jammer, make shore to have turn off switch easily accessible to switch it off quick so cops don't get suspicious, and let them measure your speed at their second attempt.
But if jamming is not illegal (probably is) in your country, then don't worry.
Good luck with research......