# Difference between gas lasers, solid-state lasers, and semiconductor lasers

Lasers used for laser welding employ gas, a solid object, or a semiconductor as the medium.
The oscillation form, output, and conversion efficiency of the laser beam output by each medium vary.
The following section takes a closer look at the features of each medium while also explaining the oscillation form, which is a major factor in laser welding.

## Laser beam differences between mediums

The following table shows the differences in oscillation form, output, and conversion efficiency between each medium.

Oscillation form (P: Pulse, CW: Continuous wave) Output (P: Pulse, CW: Continuous wave) Conversion efficiency (%)
Gas laser CO2
• P
• CW
• P: 10 MW
• CW: 20 kW
• Max. 20
Solid-state laser YAG
• P
• CW
• P: 10 MW
• CW: 400 W
• Q-switch: 10 MW
• Max. 3
Semiconductor lasers GaAs (gallium arsenide phosphide)
InGaAsP (indium gallium arsenide)
• P
• CW
• P: 10 W
• CW: 100 mW
• Max. 100

#### Oscillation forms

The oscillation form of a laser can be either pulsed or continuous. Pulse oscillation lasers generate a pulse wave by controlling (through light modulation) the intensity, wavelength, and phase of the laser beam. Methods for generating a pulse also include controlling the Q value of the laser oscillator as with Q-switch lasers. The “Q value” is the ratio of energy consumed in each cycle to the accumulated energy. This value can be expressed by the following formula.

Q = (2π / Accumulated energy) / (Energy consumed per cycle)

The shape of the weld bead also varies for each oscillation form, as shown below.

Pulse oscillation (P)

Continuous wave (CW)

A
B
Laser beam
C
Beam movement
D
Pressure

## Solid-state laser

A solid-state laser uses ore such as yttrium, aluminum, and garnet (YAG) or yttrium vanadate crystal (YVO4) as the laser medium. Because solid-state lasers have a large laser output per unit volume, a large laser output is possible even with a small resonator.

Solid-state laser

A
Full reflector
B
Laser beam
C
Excitation light source (lamp, LD)
D
YAG crystal
E
Partial reflector
F
Lens
G
Optical fiber
H
Lens
I
Workpiece

## Gas laser

A gas laser uses a gas such as CO2 as the laser medium. Compared with solid-state lasers or other laser mediums, a gas medium is more uniform with less loss, and the resonator can be larger to allow for larger laser output.

Gas laser

A
Full reflector
B
Electrode
C
Laser gas
D
Partial reflector
E
Laser beam
F
Metal mirror
G
Lens
H
Workpiece

## Semiconductor lasers

Semiconductor lasers use III-V semiconductors or IV-VI semiconductors for the laser medium. Both semiconductor types ensure device compactness while also offering a large laser output. Although semiconductors are solid objects, they are sometimes classified separately from solid-state lasers in laser technology fields.

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