Did you know that semiconductor diode has a type of laser too? This laser is extremely helpful in industries today. Let us discover more about the semiconductor lasers.
Definition
Semiconductor lasers are not only solid-state lasers like all other-solid state lasers, but they are also having their gain medium by means of a semiconductor, as well as by using stimulated emission at an inter band transition as a means of optical amplification under high carrier densities in the conduction band.
Principle
Semiconductor laser is a PN junction diode.
When engineers bring a p-type semiconductor (with excess holes) into intimate contact with an n-type semiconductor (with excess electrons), they form a junction. Supplying an external voltage in the forward biasing direction of the PN junction forces electrons from the n-region and hole carriers from the p-region into the junction.
As electrons and holes are attracted to each other, they collide and emit recombination radiation, resulting from the neutralization of the two. An electron from the conduction band (higher energy) of the n-type semiconductor neutralizes a hole from the valence band (lower energy) of the p-type semiconductor. This energy difference between the conduction and valence bands is called the band gap or forbidden energy gap of the material. The energy of the photon emitted as recombination radiation is equal to the band gap of the material for a semiconductor laser.
Characteristics
- It is a semiconductor laser in solid state.
- A PN junction diode constructed from single crystal of gallium arsenide.
- Direct conversion to be used for pumping action.
- 1mW is the output power produced by this laser.
- The continuous wave or pulses denotes nature of output.
- The gallium arsenide laser gives an infrared output in the range of 8300 to 8500 A.
Types of Laser Diodes
External-cavity diode lasers feature a laser diode as gain medium in a longer laser cavity. They are mostly tuneable, as to wavelength, and quite narrow in emission linewidths. They can also be mode-locked for ultra-short pulses at low power levels for both monolithic and external-cavity devices.
Broad area laser diodes produce. Some watts of output power with much poorer beam quality.
Surface-emitting lasers emit the laser radiation in a direction perpendicular to the wafer, delivering a few milliwatts with high beam quality.
High-power diode bars, which compose a virtual array of Broad-area emitters, produce tens of watts. All coupled with rough beam quality. Engineers use a configuration of high-power stacked diode bars to produce even higher powers, reaching several hundreds or thousands of watts.
Advantages
- Its dimensions are very small. The arrangement is also simple and compact.
- Highly efficient.
- The output of the laser can be easily increased by varying the junction current.
- Here it operates with a power requirement which is lesser as compared to ruby and CO2 laser.
- Requires very few auxiliary devices
- It can emit output in a continuous state or in pulsated waves.
Manufacturers create semiconductor lasers using various materials, such as gallium arsenide (GaAs), indium phosphide (InP), and gallium nitride (GaN). The different band gaps of these materials determine the light’s wavelength emitted by the laser.
