The device most people think of when they imagine a laser is actually a laser oscillator. A laser is actually a light amplifier. Dye laser oscillators are light sources that can be tuned to any color in the visible and near-visible portion of the electromagnetic spectrum (3900A-9000A).

Unlike other types of lasers, the dye laser amplifies light over a large range of frequencies. In this sense, the dye laser islike apublic address system, which amplifies sound over a large range of frequencies.

If the laser’s light source is, for example, incoherent and noisy, like light from an ordinary light bulb, the output light will be incoherent and noisy, only brighter, just as a public address system amplifies any noise picked up by its microphone.

The analogy with a public address system is also useful for explaining the tunable laser oscillator. Feedback squeal is emitted from a public address system when...

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