Laser Beam Properties

Introduction to Laser Beam

A laser stands for Light Amplification by Stimulated Emission of Radiation. It's a device by which electromagnetic radiation is produced, often-visible light, and to do so uses the process of optical amplification, which is based on stimulated emission of photons within a gain medium. The laser light is popular for its high degree of spatial coherence and temporal, unattainable using other technologies. As the output of spatial coherence is diffraction limited narrow beam often called pencil beam. I like to share this formula for net force with you all through my article.


Monochromatic of Laser beam


This property is based on two factors. Firstly, an EM wave of frequency `n _(0 )= (E2-E1)/h ` can be amplified; n 0 has a range which is called linewidth.  non or Inhomogeneous broadening factors and homogeneous broadening factors decide this linewidth. The linewidth is very small compared with normal lights. Secondly, a resonant system is formed by laser cavity. At resonance frequencies of this cavity, oscillation can occur. This further narrows the laser linewidth. So this makes laser light very pure in wavelength, we say it has the property of monochromaticity.


Some more properties of laser beams


Coherence

Coherence for EM wave is divided into spatial and temporal coherence. If two points are considered such that both lie on the same wave front of given EM wave, at time t=0. The phase difference at these points on EM wave at time t=0 is k0. For time t>0 if the EM wave phase difference at two points remains k0, we say that there is perfect coherence in EM wave between the two points. Having problem with Electric Current Formula keep reading my upcoming posts, i will try to help you.

Now we take a fixed point on EM wave front. If the phase difference remains same at any time between time t and time t+dt, where "dt" denotes time delay period, the wave is said to have temporal coherence over time dt. If dt is any value, we called the EM wave to be perfect temporal coherence wave.  The high coherent property of laser is used in measurement, holography, etc.

Divergence and Directionality

Laser beam has very small divergence and therefore, is highly directional. This shows that laser beam appear from resonant cavity and waves that propagate along optical axis are sustained in cavity. Light beam divergence angle describes the directionality.
From diffraction theory, the divergence angle` theta_(d)` is:

`theta_(d)= (beta lambda) /D`

Where l= wavelength, D= diameter of beam, b= coefficient of value around unity, Θ = divergence

Brightness

The power released per unit solid angle per unit surface area is known as the brightness of laser beam. If beam of laser has power P, cross section of beam has diameter D and Θ being the divergence angle then the resulting emission solid angle is πΘ2, and then brightness is given by:

`"B=(4P)/(pi D theta)^(2) ` .