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 GaAsP (gallium arsenide phosphide)
InGaAs (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)

Pulse oscillation (P)

Continuous wave (CW)

Continuous wave (CW)
A
Weld bead
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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