1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Laser that doesn't have a resonator?

  1. Oct 25, 2015 #1
    Is it possible to have a laser without a resonator? My guess is you can as you would still get some proportion of light coming from the inverted medium. My question is how would this light be different (from that of a laser with a resonator) and are there any practical uses for such a device?
  2. jcsd
  3. Oct 25, 2015 #2
    It would appear so. The following Wikipedia article has a reference for a single pass nitrogen laser (ref 9) which does not have a resonant cavity.
    https://en.wikipedia.org/wiki/Laser i.e. "Nitrogen Laser". Light and Its Uses. Scientific American. June 1974. pp. 40–43. ISBN0-7167-1185-0.
  4. Oct 25, 2015 #3


    User Avatar
    Gold Member

    I can’t see how that would work. The high Q of the resonator is what gives laser light its temporal coherence. Without the resonator all you would have is spontaneous emission plus a bit of amplified spontaneous emission (ASE).
  5. Oct 27, 2015 #4

    Have a look at the Wikipedia article. I haven't yet tracked down the Sci. Am. article from 1974 to see whether it casts any light on the matter. I too originally thought that a cavity resonator was essential for laser operation,. The Wiki article does mention use of a mirror at one end but no half silvered mirror at the exit end. I guess the Light Amplification by Stimulated Emission is the critical part that can take place without the cavity as long as the population inversion is achieved by pumping. The efficiency and spatial and temporal coherence are no doubt improved by a high Q cavity. I'll ask a few colleagues who work on laser physics for their insights. I might try a search for papers on lasers without cavities and see what turns up.
  6. Oct 27, 2015 #5


    User Avatar
    Gold Member

    Interesting - thanks Dave. I clicked through onto the Nitrogen laser page where it says they work on the superluminescence principle. Superluminescence is just ASE but the gain is so high you can get a useable beam without a cavity.

    One of the references on that page was this, with lots of info on N2 lasers:

    It seems that the lower lasing level in N2 is metastable so it wouldn’t work CW and the gas is pumped by an arc discharge which is too brief to establish resonance in a cavity anyway. So people just leave out the mirrors and get a bright beam of ASE with each discharge.

    That page above claims it’s coherent, but I can’t get my head around that. Any ideas?
  7. Oct 27, 2015 #6

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor

    As mentioned above, solid state lasers can be highly lossy because the gain is also high- they essentially function as single-pass amplifiers. There are also unstable resonator designs which can be used in high power applications.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Laser doesn't resonator Date
Laser causing gravity? Today at 3:13 PM
I Laser Safety Glasses question Mar 14, 2018
B Why parts of the laser ray seem brighter than other parts Mar 6, 2018
B Repeating Laser beam Xnm Feb 28, 2018
Why Raman spectroscope doesn't use 532nm laser ?. Feb 28, 2018