Laser
Excitation Method and Oscillation Method
Excitation method
The atom (Or,molecular) in the laser medium is necessary to be for the laser to oscillate in the state of the population inversion.
The energy supply from the excitation source is necessary to cause the population inversion.
There is the following kinds of the means.
| method | explanation |
| discharge excitation | Many of gas lasers are excited by the electrical discharge. The glow discharge and the arc discharge are used. |
| optical excitation | Many of solid lasers and liquid lasers are excited by light.A big lamp or laser is used. |
| electron beam excitation | The electron that accelerates to the vicinity of speed of light is called relativism electron beam (REB) by the voltage of a high-speed pulse of 500kV or more. It excites it by using relativism electron beam (REB). |
| chemical excitation | It excites it by the energy obtained by the chemical reaction. The energy supply from the outside is not needed. |
| Current excitation | The laser medium is excited by injecting the current.It is chiefly used by the semiconductor laser. |
| thermal excitation | The laser medium is excited by using thermal energy. |
Oscillation method
In the oscillation method, there are continuous wave oscillation (CW) and pulse oscillation (P).
The pulse oscillation is divided into the normal pulse oscillation and Q switch pulse oscillation further.
| method | explanation | |
| continuous wave oscillation(CW) | It oscillates continuously a constant output. | |
| pulse oscillation(P) | normal pulse oscillation | One shape of waves of the pulse can be controlled. |
| Q switch pulse oscillation | It is possible to oscillate at equal intervals the irradiation of big energy. This is a method of waiting until the population inversion happens enough in the laser medium, and oscillating the laser instantaneously. Because energy is instantaneously liberated, one shape of waves of the pulse cannot be controlled in detail. |
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The oscillation method is "Q switch pulse oscillation" as for a big peak value and the laser of a short pulse.
The value in which the light energy accumulated in the resonator is divided due to the loss is called Q value.
First of all, the pumping is made to be progressed like a low state Q value of the resonator.
The laser doesn't oscillate because the loss of the resonator is large. The state of the population inversion becomes larger as it is.
The laser oscillation happens instantaneously when Q value is rapidly raised when the population inversions reach highest.
The laser that the peak value is large, and the pulse is short is irradiated.
It is called Q switch to switch Q value.