Health

Q&A: What are seborrheic keratoses?

Dear Mayo Clinic: I have brown spots over the top half of my body, which my doctor says are seborrheic keratoses and are harmless. What causes them, and is there a way to prevent more from appearing?

Diseases, Conditions, Syndromes

What works best against varicose veins?

More than 40 million Americans suffer from varicose veins, which can be both unsightly and painful, but the best way to get rid of them hasn't been clear.

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Laser

A laser is a device that emits light (electromagnetic radiation) through a process called stimulated emission. The term laser is an acronym for light amplification by stimulated emission of radiation. Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low-divergence beam, or can be converted into one with the help of optical components such as lenses. Typically, lasers are thought of as emitting light with a narrow wavelength spectrum ("monochromatic" light). This is not true of all lasers, however: some emit light with a broad spectrum, while others emit light at multiple distinct wavelengths simultaneously. The coherence of typical laser emission is distinctive. Most other light sources emit incoherent light, which has a phase that varies randomly with time and position.

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