Semiconductor laser working principle and parameter description
Semiconductor laser, also known as laser diode (LD, Laser Diode), is a type of laser that uses semiconductor materials as the working material and produces excited emission. Commonly used materials are gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS). Excitation methods are electric injection, electron beam excitation and optical pumping excitation in three forms.
Semiconductor laser devices, in general, can be divided into homojunction, single heterojunction, double heterojunction. Homojunction lasers and single heterojunction lasers are mostly pulsed devices at room temperature, while double heterojunction lasers can achieve continuous operation at room temperature. Its advantages are small size, light weight, reliable operation, low energy consumption, high efficiency, long life and high speed modulation, so it has been widely used in laser communication, optical storage, optical gyroscope, laser printing, laser medical, laser ranging, laser radar, automatic control, testing instruments and other fields.
Working principle of semiconductor laser
Through a certain excitation method, the particle number reversal of non-equilibrium carriers is realized between the energy band (conduction band and valence band) of semiconductor material, or between the energy band of semiconductor material and impurity (host or sender) energy level, and the excited emission is produced when a large number of electrons and holes in the particle number reversal state are compounded.
There are three main excitation methods for semiconductor lasers: electric injection, electron beam excitation and optical pump excitation. Electrically injected semiconductor lasers are generally made of GaAS (gallium arsenide), InAS (indium arsenide), Insb (indium antimonide) and other materials made of semiconductor surface junction diodes, along the forward bias injection current for excitation, in the junction plane region to produce excited emission. Electron-beam excited semiconductor lasers generally use N-type or P-type semiconductor single crystals (PbS, CdS, ZhO, etc.) as the working material, and are excited by externally injected high-energy electron beams.
Light-pumped excitation semiconductor lasers generally use N-type or P-type semiconductor single crystals (GaAS, InAs, InSb, etc.) as the working substance, and are excited by the laser light from other lasers.
At present, in the semiconductor laser device, the better performance, the more widely used is: with double heterogeneous structure of electric injection GaAs diode semiconductor laser.
The operating wavelength of semiconductor optoelectronic devices is related to the type of semiconductor material. Semiconductor materials exist in the conduction band and valence band, the conduction band above the free movement of electrons, and the valence band below the free movement of holes, the conduction band and the valence band between a forbidden band, when the electron absorbed the energy of light from the valence band jumped to the conduction band when the energy of light into electricity, and with the electrical energy of the electron from the conduction band jumped back to the valence band, and can turn the energy of electricity into light, then the width of the forbidden band of the material to determine the The width of the forbidden band of the material determines the working wavelength of the optoelectronic device.
The main parameters of semiconductor lasers.
Wavelength nm: laser working wavelength, such as 405nm, 532nm, 635nm, 650nm, 670nm, 690nm, 780nm, 810nm, 860nm, 980nm.
Threshold current Ith: the current at which the laser diode starts to generate laser oscillation, its value is about tens of milliamps for low power lasers.
Operating current Iop: the driving current of the laser diode when it reaches the rated output power, this value is more important for the design and debugging of the laser drive circuit.
Vertical dispersion angle θ⊥: laser diode light-emitting band in the vertical direction with the PN junction open angle, generally in 15 ° ~ 40 ° or so.
Horizontal dispersion angle θ∥: laser diode light-emitting band in the parallel direction with the PN junction open angle, generally in 6 ° ~ 10 ° or so.
Monitoring current Im : laser diode in the rated output power in the PIN tube current flow.
Semiconductor lasers are mainly developed in two directions: one is to transmit information-based lasers; the other is to improve the optical power of the main power laser.
