Laser

Laser

Here you will learn about,

Introduction of Laser:

Definition:

Light Amplification by Stimulated Emission of Radiation.
A laser is a device that induces the emission of light at certain wavelengths from atoms or molecules and amplifies that light, usually creating an extremely narrow beam of light. 
As a general rule, Laser light is formed when a specific wavelength of light usually UV-visible and IR, hit a matter, and electrons are ejected from matter in the form of light. 

History of Laser:

The invention of the laser is credited to Albert Einstein, who postulated that under certain circumstances, atoms might spontaneously or in response to a light release an excess of energy. Light, he argued, was what first created the laser. Although stimulated emission didn't seem to have any applications at the time, German scientist Rudolf Walther Ladenburg made the first observation of it in 1928.

When Charles H. Townes was a student at Columbia University in New York City in 1951, he had the idea to create stimulated emission at microwave frequencies. Townes goes on to refer to this as a maser, which stands for "microwave amplification by the stimulated emission of radiation."

Nikolay Gennadiyevich Basov of the P.N. Lebedev Physical Institute in Moscow and Aleksandr Mikhaylovich Prokhorov independently established the theory of maser operation. Each of them shared the 1964 Nobel Prize in Physics in recognition of their contributions.

Townes,suggested to Arthur L. Schawlow, (his brother-in-law's former law postdoctoral student at Columbia University who was working at Bell Laboratories at the time) proposed that they try to expand maser activity to the relatively short wavelengths of visible light and IR light. Townes also talked with Gordon Gould, a Columbia University Ph.D. candidate. Gordon Gould started coming up with his own laser ideas right away.

In a groundbreaking study that appeared in the Physical Review edition of December 15, 1958, Townes and Schawlow presented their concepts for an "optical maser." Gould simultaneously created the term "laser" and submitted a patent application. Thus, the question of who should be given credit for "inventing" the laser—Townes or Gould—became the subject of heated discussion and years of court battles. In the end, Gould was granted four patents beginning in 1977, which brought in millions of dollars in royalties for him.

Theodore H. Maiman, who used a different strategy at Hughes Research Laboratories in Malibu, California, saw success initially. He used a synthetic ruby crystal as the target because he had carefully examined how it absorbed and emitted light and determined that it should function as a laser. To excite the chromium atoms in the ruby crystal, he shot intense pulses using a photographer's flash lamp. He created red pulses on May 16, 1960, using a ruby rod that was approximately the size of a fingertip. Laser beams were anticipated to be employed in fundamental research and for sending messages into the atmosphere or space by Townes and Schawlow.

Properties 

1.       It is coherent. 
2.       It is monochromatic. 
3.      It has a single wavelength and one specific color.

Based on these properties, we can distinguish between ordinary light and laser light.

LASER light formation:

Some basic terms to understand laser light formation:

Active medium:

The active medium is a type of material that maintains the phenomenon of stimulated emission, and population inversion and produces light by amplification. It can be a solid, liquid, or gaseous state and able to maintain a metastable state for population inversion.     

Metastable state:

A state that has a lifetime more than the excited state and it is necessary for population inversion. For example, the Ruby laser lifetime of atoms in an excited state is 10^-8.

Laser cavity:

A technique for optical confinement designed to extend radiation's gain length before it leaves the device. Depending on the characteristics of the intended beam within the lasing medium, several optical confinement techniques are utilized to lengthen gain paths. Dielectric mirrors coated for the laser wavelength are employed because high light intensities are present inside a laser cavity. To enhance the laser performance for a certain application, the optical cavity components' location and curvature can be changed.

Population inversion:

It is a phenomenon that is required for stimulated emission. Here the number of high energy levels is more as compared to lower energy levels. Active medium and metastable state is necessary for population inversion.

Spontaneous emission:

If electrons jump to the ground state by releasing energy or photon of light for stability, then this is called spontaneous emission.

Stimulated emission:

If electrons jump to the ground state by releasing energy or photon of light and an additional photon of light for stability, then this is called stimulated emission.

Process of Laser light formation:

Laser light Formation

In an atomic system, there are discrete energy levels, initially most of the electrons are present in a lower energy level which is called the ground energy state or level. when atoms are excited they go to a high energy level from the lower level and then de-excite jumps to a lower energy level spontaneously by emitting a photon of light. But if we use other sources to de-excite atoms for example electricity or chemical energy and use continuous sources for de-excitation (pumping) then atoms release a photon of light and an additional photon of light is also emitted because we use other sources for de-excitation. This is called stimulated emission. These photons reflect back in the active medium (matter) and eject more photons of light, these photons go to the laser cavity where amplification of light occurs and a very fine beam of light is emitted, this is called laser light.  

Laser Diagram

Types of Laser:

Five different laser types serve as the foundation for active medium lasers.

1.       Liquid laser
2.       Gas laser
3.       Solid laser
4.        Semiconductor laser
5.       Fiber laser                                                                              

Uses of laser     

1. Unquestionably, CO2 lasers, which are frequently used for laser cutting, welding, and marking, are the most well-known gas lasers.
2. Lasers are used in optical disc drives, barcode scanners, laser printers, DNA sequencing devices, free-space optoelectronic devices, optical fiber.
3. Semiconductor machine manufacturing "photolithography," skin and laser therapies, welding and cutting materials, and equipment for law enforcement and the military.