### About Population Inversion in Laser - Definition, Diagram

Do you want to know about population inversion ? Here is the complete information on this topic of laser population inversion.In this we discuss in details on this topic.Laser light is totally different from conventional light.
In conventional light sources,there is no coordination among different atoms emitting radiation.
There will be a population inversion occurs where more atoms are present in high energy states than in low ones.

# Introduction

Population inversion is explained by levels E1, E2 and E3 of a system.Explain that E1, E2 and E3 are the excited states of ground state, metastable state, and system energies, respectively, such as E1 <E2 <E3. In a system, the population of atoms (N) at an energy level E, expressed at absolute temperature T .In terms of population (N1) in the ground state using Boltzmann's distribution law.

N = N1 exp (−E / KBT ) where KB = Boltzmann’s constant

 population inversion diagram

### Definition of Population inversion

Generally, the number of atoms (N1) present in the ground state (E1) in the system is larger than the number of atoms (N2) present in the high energy state. The process of making N2> N1 is called the population inverse.

#### Conditions for population inversion

These are the Conditions for population inversion :

(a) The system must have a pair of at least one energy level (E2> E1), separated by an energy equal to the energy of a photon (hν).

(b) There should be a continuous supply of energy to the system such that atoms must be continuously raised in excited state.

#### How Population inversion can be achieved

Population inversion can be achieved by following numbers of ways. Some of them are:
(i) optical pumping
(ii) electrical discharge
(iii) inelastic collision of atoms
(iv) chemical reaction and
(v) direct conversion.
In lasers, if the active medium is a transparent dielectric, the optical pumping method is used. If the active medium is conductive, the electric field is used to produce a population inverse.

### About N-Type and P-Type Semiconductor | Materials | Example |

Here you will know about  n type and p type semiconductor in details. You can already see about bonding in semiconductor . N type and P type semiconductor is used in electronic appliances.which is the basis of working of all the electronic devices.So lets discuss in this given topic in the details. N type and P Type Semiconductor When some impurities added to the pure semiconductor then it becomes extrinsic semiconductor and this process of adding impurities is known as doping.  Now it depends on the which type of impurities it added to the semiconductor (two types of impurities can be added to semiconductor pentavalent or trivalent). n-type semiconductor : If impurity that is added to the pure semiconductor is a pentavalent ( which has five valance electron ) then it is called n-type semi conductor. p-type semiconductor : If trivalent impurity is added to the semiconductor then it becomes p-type semi conductor. ( Note-List of  n type and p type semiconductor material is given below.

### Biasing of p–n Junction | Forward and Reverse-biased |

Biasing the p-n junction means applying some external voltage to both sides of the p-n junction. Reverse-biased junction and forward-biased junction are two types of biased junction. You should have also good understanding of  N-Type and P-Type Semiconductor before moving towards this topic. Biasing of p–n Junction  Biasing of a p–n junction  means uses of some external voltage across the two sides of the p–n junction. It is divided into two groups  Forward-biased junction :  When the p-side of junction  is connected to the positive terminal of a battery and the n-side of junction is connected to the negative terminal, the p–n junction is said to be a forward-biased junction.  Reverse-biased junction  :If the positive terminal of the battery is connected to the n-side of junction and the negative terminal on the p-side, the p–n junction is said to be a reverse-biased junction. Now we will see about forward and reverse-biased junction in detail.  Related Topic    Bonding in semiconduc

### Engineers Files Explained | Types of file

Today we will learn about engineers files explained, as we know hand tools are used to remove small amounts of material, usually from small areas of the workpiece.   Do you know why hand tools are used ?Hand tools are used because of following reason: If no machine is available,  The workpiece is too large to go on a machine  The shape is too intricate or simply that it would be too expensive to set up a machine to do the work. As you know the necessity of a hand tools now we will know about a hand tool , engineer's files. Engineer’s files Files are used to perform a variety of tasks, from simple removal of sharp edges to producing complex shapes where use of the device is impractical.Files can be obtained in a variety of shapes and in lengths from 150 mm to 350 mm. Single-cut file: When a file has a single series of teeth cut across its face it is called  single-cut file ,Figure of single-cut file is shown below. double-cut file: When a file has double series of teeth cut across