A semiconductor laser, also known as a diode laser, is a device that emits coherent light through the process of stimulated emission. It is based on the principle of an optoelectronic device called a semiconductor diode. The laser diode is one of the most common types of lasers used in various applications, including telecommunications, optical storage, laser printing, barcode readers, and laser pointers.
Here's a brief overview of how a semiconductor laser works :
Structure: A semiconductor laser typically consists of a semiconductor diode made from a compound such as gallium arsenide (GaAs) or indium gallium arsenide phosphide (InGaAsP). The diode is constructed by sandwiching a p-type (positive charge) semiconductor layer between n-type (negative charge) semiconductor layers. This forms a p-n junction, which is the key component of the laser.
Injection and recombination: When an electric current is applied to the diode, electrons from the n-type side and holes from the p-type side are injected into the junction region. The electrons and holes recombine, releasing energy in the form of photons.
Population inversion: Through a process called optical pumping, more electrons are excited into higher energy levels than there are in the lower energy levels. This creates a population inversion, where there is a higher concentration of electrons in the excited state.
Stimulated emission: When a photon passing by an excited electron stimulates it to move to a lower energy state, it releases a new photon with the same wavelength and phase. This process triggers a cascade effect, resulting in the emission of a coherent beam of light.
Optical feedback: To create a laser beam, the diode is placed between two reflective surfaces, forming an optical cavity. One of the surfaces is fully reflective, while the other is partially reflective to allow a portion of the emitted light to escape as the laser beam.
Laser operation: The injected current sustains the population inversion, and the photons undergo stimulated emission, leading to a self-sustaining oscillation of light between the mirrors. This coherent output light passes through the partially reflective mirror, forming the laser beam.
Semiconductor lasers have numerous advantages, including small size, high efficiency, low power consumption, and direct modulation capabilities. These properties make them suitable for a wide range of applications, particularly in the field of optical communication where they are used in fiber optic networks to transmit data over long distances.
