Laser Diodes

• The laser is a basic device which amplifies the light, hence the LASER full form is an acronym for light amplification by stimulated emission of radiation.
• The operation of the device may be described by the formation of an electromagnetic standing wave within a usage a cavity (optical resonate) which provides an output of monochromatic highly coherent radiation.
• There are different types of LASER used like single-Mode Lasers and Modulation of Laser Diodes, depends on which types of application is used.
• The output of laser diodes characteristics is depends on the drive current passing through it. In laser diode operating at low drive current, it operates as an inefficient LED full form when driving current crosses threshold value and lasing action begins.
• An injection laser is also known as a laser diode or diode laser. It is a semiconductor device, Nowadays it can be used many application or devices like optical fiber, compact disk, remote control device etc.
• In LASER diode the power current characteristics, the threshold current only spontaneous emission is emitted hence there is a small increase in optic power with drive current.

Principle :

• The material absorbs light rather than emitting. Three fundamental processes occur between the two energy states of an atom. 

1. Absorption 

2. Spontaneous emission 

3. Stimulated Emission. 

• Laser Action is the result of three process absorption of energy packets (photons) spontaneous emission, and stimulated emission. (These processes are represented by the simple two-energy-level diagrams) 

Where,

• E1 is the lower state energy level.
• E2 is the higher state energy level. 

• Quantum theory states that any atom exists only in certain discrete energy state, absorption or emission of light causes them to make a transition from one state to another. The frequency of the absorbed or emitted radiation f is related to the difference in energy E between the two states.

• If E1, is lower state energy level and E2, is higher state energy level.

E = E1 - E2 = h.f.

You may also know advantages and disadvantages of laser diode know more details about laser diode.

Advantages of Laser Diode

• Simple economic design.
• Better modulation capability.
• It gives high optical power.
• Laser diode is smaller size as compared to other types of laser.
• Production of light can be precisely controlled.
• Ability to transmit optical output powers between 5 and 10 mW
• Low spectral width (3.5 nm).
• Laser diode has high coupling efficiency.
• It can be used at high temperatures.
• Laser diode is the cheaper device to produce laser output.
• Ability to maintain the intrinsic layer characteristics over long periods.

 Disadvantages of Laser Diode 

• A speckle pattern appears as two coherent light beams add or subtract their electric field depending upon their relative phases at the end of the fiber.
• In laser diode use of large drive current produces unfavorable thermal characteristics and necessitates the use of cooling and power stabilization.
• It produces more divergent laser beam
• Expensive
• Poorly absorb in hard tissue and hydroxyapatite