> What is also remarkable: Plane electromagnetic waves like a light beam normally cannot cause permanent velocity changes of electrons in vacuum, because the total energy and the total momentum of the massive electron and a zero rest mass light particle (photon) cannot be conserved. However, having two photons simultaneously in a wave traveling slower than the speed of light solves this problem (Kapitza-Dirac effect).

> For Peter Baum, physics professor and head of the Light and Matter Group at the University of Konstanz, these results are still clearly basic research, but he emphasizes the great potential for future research: "If a material is hit by two of our short pulses at a variable time interval, the first pulse can trigger a change and the second pulse can be used for observation—similar to the flash of a camera."

Chirped Pulse Amplification: https://en.wikipedia.org/wiki/Chirped_pulse_amplification

What Hz rate is necessary to do CPA Chirped Pulse Amplification with laser, or with a [blue] LED? FWIU lasers have a repetition rate between 0.1Hz and 1Mhz, and a pulse width between 1 picosecond and 1 millisecond?

Looks like there are already commercial LED CPA systems.

Aren't there also weird signal effects with e.g. PWM and a blue led connected to a Pi with a sufficient clock rate? What are the maximum binary data transmission distances for [blue] LEDs?

How to fade an LED in and out when you can only vary 5volts on and off? PWM: Pulse Width Modulation; you vary the duty cycle:

PWM: https://en.wikipedia.org/wiki/Pulse-width_modulation

"Learn PWM signal using Wokwi Logic Analyzer" https://blog.wokwi.com/explore-pwm-with-logic-analyzer/

Wokwi > New (Pi Pico w/ Micropython) LED project: https://wokwi.com/projects/300504213470839309