Register to reply

Laser: CW-oscillation in a 3-level laser

by Niles
Tags: 3level, cwoscillation, laser
Share this thread:
Dec28-09, 10:20 AM
P: 1,863

At continuous-wave oscillation the gain is equal to the threshold gain, i.e. g = gthreshold. Now in my book, I have the following expression for the steady-state population-inversion for a three-level laser

N2, steady state - N1, steady state = (P-Γ12)/(P+Γ12)NT

where NT=N1, steady state+N2, steady state, P is the pump rate and Γ12 is the rate at which level 2 decays into level 1. Now my question is: If at CW-oscillation g=gt, then why is it that we can change N2, steady state - N1, steady state (and thereby the gain) in a three-level laser at steady-state? Isn't this a contradiction?
Phys.Org News Partner Physics news on
Technique simplifies the creation of high-tech crystals
Working group explores the 'frustration' of spin glasses
New analysis of oxide glass structures could guide the forecasting of melt formation in planetary interiors
Dec28-09, 12:41 PM
Sci Advisor
P: 1,626
What happens if you increase the pumping power further after laser oscillation sets in, is called gain clamping or upper population clamping. Any atoms you pump into the upper level will be almost immediately converted into laser light as fast as you pump them up (well - on statistical average, of course not necessarily the same atoms you just pumped up). Therefore the decay rate will also momentarily increase. If you do not increase the pump power constantly but just add short pulses of high pump power, you might also see the population numbers and the intracavity photon number undergo relaxation oscillations according to the fluctuation-dissipation theorem.

Register to reply

Related Discussions
Intensity of red laser vs blue laser Advanced Physics Homework 4
Would it be possible to produce a dif laser by 382nm UV diode laser with a 910nm IR Classical Physics 3
Diffusion of laser light for measuring laser power General Physics 3
Double slit problem, finding λ of second laser given data about first laser... Introductory Physics Homework 2