A laser operates on the fundamental principle that a pumped medium amplifies a travelling light beam as it propagates through the medium. Without mirrors a laser becomes a single-pass travelling wave amplifier (Figure E.26.1).
This is a system without feedback. If we now place mirrors at each end of the pumped medium, we introduce feedback into the system.
When the gain of the medium becomes large enough the system oscillates creating a coherent output light beam. That is laser operation. If the gain of the medium is less that that required to sustain oscillation, the system is known as a regenerative travelling-wave amplifier (RTWA).
Let the electric field of a light beam incident on the RTWA from the left be the excitation of the system, Einc(s), and let the electric fields of the reflected light, Erefl (s), and the transmitted light,
Etrans (s), be the responses of the system (Figure E.26.3).
You might also like to view...
Lime makes the soil acidic and is harmful to root development
Indicate whether the statement is true or false
Why might mixing valves be used for radiant floor heating?
What will be an ideal response?
If there is 1 ARMS through the resistor and 1 ARMS through the capacitor in a parallel RC circuit, then the total current equals ________
A) 1 ARMS B) 1.41 ARMS C) 2.28 ARMS D) 2 ARMS
Fluid power ancillary devices may include: accumulator, conditioning systems, and ________.
A. feedback sensors B. seals C. connecting devices D. All answers are correct