Master Oscillator Power Amplifier | previous | next | feedback |
(Acronym: MOPA)
Definition: a laser system consisting of a seed laser and a laser amplifier for boosting the output power
The term master oscillator power amplifier (MOPA) refers to a configuration consisting of a master laser (or seed laser) and an optical amplifier to boost the output power. A special case is the master oscillator fiber amplifier (MOFA), where the power amplifier is a fiber device.
Although a MOPA configuration is in principle more complex than a laser which directly produces the required output power, the MOPA concept can have certain advantages:
- With a MOPA instead of a laser, it can be easier to reach the required performance e.g. in terms of linewidth, beam quality or pulse duration if the required power is very high. This is because aspects like linewidth or pulse generation are to some extent decoupled from the generation of high powers. This gives extra flexibility, e.g. when a gain-switched laser diode is used as a seed laser.
- The same aspects apply to other kinds of modulation, e.g. intensity or phase modulation: it may be advantageous to modulate the low-power seed laser, or to use an optical modulator between seed laser and power amplifier, rather than to modulate a high-power device directly. Slower power modulation may be done by adjusting the amplifier's pump power, without significantly affecting e.g. the obtained pulse duration or wavelength.
- The combination of an existing laser with an existing amplifier (or an amplifier chain) may be simpler than developing a new laser with higher output power.
- The optical intensities are lower in an amplifier, compared with the intracavity intensities in a laser.
However, the MOPA approach can also have disadvantages:
- The complexity of the setup is higher.
- The wall-plug efficiency is often (but not always) lower.
- The resulting laser noise tends to be higher, since an amplified source can not reach the shot noise level (→ amplifier noise). Effects of drifts of the seed power may however be suppressed if the amplifier is operated in a strongly saturated regime.
- A MOPA can be rather sensitive to back-reflections, which are amplified again before getting into the master laser. This feedback sensitivity can often be cured only by placing an optical isolator behind the amplifier. Particularly for high-power pulsed devices, this can introduce serious limitations.
See also: amplifiers, master oscillator fiber amplifier, amplifier noise
Categories: amplifiers, lasers
