# What is the meaning of "CW" in LASER?

I am reading a user's manual, and the word appears here. At first, I think "CW" means "center wave". But later, I find that the meaning of "CW" is "continuous wave".

It makes me confused. Generally, Laser has a unique frequency. Properly speaking, it has a too small fluctuation of frequency, or line width, such that we can treat the spectrum as harmonic wave which has a unique frequency.

So, literally, dose "continuous wave" means a wave which is not interrupted? Is it the same as "harmonic wave"?

• At first, I think it means "center wavelength" Jul 29 '13 at 12:07
• It means continuous wave. Jul 29 '13 at 12:12

Lasers typically operate in two regimes: as CW or continuous wave (the radiation leaving the laser cavity or resonator continuously by a partially reflecting mirror, or as you put it, forming an uninterrupted wave) or as a laser pulse (the radiation leaving the cavity during a short time at a repetition rate, that is, as a burst of short pulses very separted between each other). In the latter case the laser is not monochromatic and its spectral width can be very large. Indeed, recently sub-femtosecond laser pulses ($10^{-15}$ s) have been produced, thus with bandwidths larger than $1$ eV.