In contrast to the previous light sources, laser diodes produce a narrow beam of laser light in which all the light waves have similar wavelengths and they travel together with their peaks lined up. This process is called absorption. This type of laser diode is also called as a “Homojunction Laser Diode”.

The natural white light is made up of all the VIBGYOR colours of the visible light spectrum, which is a broad wide band of many different frequencies. If the current reduces and falls below the threshold current, stimulated emission ceases; just a little too much current and the diode is destroyed.As the active layer is filled with oscillating photons, some (typically about 60%) of the light escapes in a narrow, flat beam from the edge of the diode chip.

But for controlling a laser diode used in applications where high accuracy is not required, a simple laser diode driver circuit can be constructed using LM317 voltage regulator IC. Until this point, most of the light emitted is due to spontaneous emission. For any stimulated emission.It is necessary that the upper energy level or met stable state should have a long lifetime, i.e., the atoms should pause at the met stable state for more time than at the lower level. For this reason, the current through the laser diode must be carefully regulated.Another problem is that the emission of photons is very dependent on temperature, the diode is already being operated close to its limit and so gets hot, therefore changing the amount of light emitted (photons) and the diode current.

(Here, a hole means the absence of an electron).

Therefore, each colour will focus at different points, causing ‘chromatic aberration’. The The above figure shows a simplified construction of a laser diode, which is similar to a Every atom according to the quantum theory, can energies only within a certain discrete energy level. The 47uF capacitor is used to absorb any battery voltage spikes.Laser Diode modules are used in all major areas of electronics ranging fromTypes of Diodes | Small Signal, LED, Schottky, Zener Thus, for laser action, pumping mechanism (exciting with external source) should be from a such, as to maintain a higher population of atoms in the upper energy level relative to that in the lower level.It is necessary that the upper energy level or met stable state should have a long lifetime, i.e., the atoms should pause at the met stable state for more time than at the lower level. A partially reflecting mirror is used on either side of the diode so that the photons released from spontaneous emission are trapped in the p-n junction until their concentration reaches a threshold value. It uses p-n junction to emit coherent light in which all the waves are at the same frequency and phase. This allows more number of electrons to recombine with holes at any instant of time, resulting in better output power. Laser Diode Working Principle A laser diode , or LD also known as injection laser diode or ILD , is an electrically pumped semiconductor laser in which the active laser medium is formed by a p-n junction of a semiconductor diode similar to that found in a light-emitting diode. The partially reflecting mirrors are placed near the ends of optical cavity.Vertical External Cavity Surface Emitting Laser Diode (VCSEL)The below diagram is a graphical plot between output optical power on y-axis and the current input to the laser diode on x-axis.As we increase the current flow to the laser diode, the optical power of output light gradually increases up to a certain threshold.
When an energy source given to the atoms in the ground state can be excited to go to one of the higher levels.
The advantage of this DH laser diode is that that the active region is confined to a thin layer which gives better optical amplification.The quantum well laser diode has a very thin middle layer, which acts as a quantum well. Above this threshold current, the process of stimulated emission increases. Normally, the atoms are in the lowest energy state or ground state. When a certain voltage is applied at the p-n junction, the electrons absorb energy and they transition to a higher energy level. The intrinsic region between the p-type and n-type material is used to increase the volume of active region, so that more number of holes and electrons can accumulate at the junction.

Normally, when the material is not excited externally, the population of the lower level or ground state is greater than that of the upper level. This results in the release of more photons that are in exact phase with the initial photons and so the output gets amplified.