Expert: Daniel Mazur - 7/3/2006

Question
Dear sir :
We are a group of physics and chemistry teachers following a professional development course . We would be happy if you answer our questions regarding the subject we teach .
1 – What are the uses of laser recently discovered?
2 – Why don't the electromagnetic waves spread in the physical environment ?
3 –Do you have any new information concerning the Black Hole ?
Thank you  

Answer
Hello,

I am not an expert on electromagnetic waves/light, nor black holes. I will answer the questions 1 and  2 the best I can, I am really not able to help you with the third one.

1) (not clear what 'recently' means for you) At college (~7 years ago) I learned about a new, at that time, discovery of laser cooling. The idea was that if you mix a beam of 'hot' particles with a laser beam, the two thermalize (laser beam photons drag some 'heat' from the other beam) and then you use magnetic field to separate the beams again. The result is a beam of particles with really low thermal spread, i.e. really 'cold'.
Secondly, hat we are using frequently in solid state physics is so called 'laser ablation'. You create a high-power laser beam and use it (usually in pulsed mode) to sputter material of a chosen target. Some particles of the material land on a substrate and re-form in a thin film, which has the same chemical composition as the target had. We use this because thin films have properties very different from bulk materials and because films are essential in applications.
The third rather new use of laser I stumbled upon recently: a high-current switching element. When you have a wafer of pristine silicon, it is pretty much insulating. You can load it with some good voltage and it will stay so, virtually no losses. Now, when you irradiate the biased wafer with a laser, you change its character from insulating to conducting. If the voltage source has large enough capacity, you can this way let flow a current ~10,000 Amps. through your circuit, because the high current maintains the excited (conductive) silicon state, which had been created by the initial laser pulse.

2) Electromagnetic waves DO spread in the environment! Waves are demonstrations of collective behavior of particles (photons in case of EM waves) and as such they spread. The proof being the inverse square-root law of intensity vs. distance from a point source of radiation. I feel I might not have understood this question the way it had been meant, please post a follow-up question, if needed.

3) I have no knowledge about black holes, I apologize.

I hope I helped a little bit.
Daniel