Laser linewidth broadening caused by a laser amplifier

It is shown that a laser amplifier connected to a laser will broaden the linewidth with a factor on the order of the laser multiplier power gain. The laser linewidth can be broadened in comparison to the free-running linewidth if the laser is connected to a laser amplifier because the noise emitted by the amplifier enters the laser and perturbs the oscillation. The broadening factor can be reduced to unity by inserting an isolator between the laser and the laser amplifier.<
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