What is the meaning of "CW" in LASER?

Question

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"?

Answer 1

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.

Answer 2

The choice between continous or pulsed can come down to the power output of the laser. For the same input power you can either output that power at some constant and therefore the average power is equal to the peak, or send the energy out in pulses. In pulsed mode the peak energy can be much higher while maintaining the same average power.