Why laser is needed in holography

As recording process in holography is based on the principle of interference. For recording and for sustained interference, the path difference between various interfering light waves should always be less than longitudinal coherence length. For ordinary light source like mercury the coherence length is very small (≈3cm). The path difference introduced between light waves reflected from different points of object can be much more than this value. Thus interference pattern cannot be recorded. While coherence length for laser source can be as high as 600 km. As a result, sustained interference pattern will be recorded on hologram. Thus hologram cannot be made without laser source. Continue reading “Why laser is needed in holography”

Reflection and transmission hologram

Reflection hologram: If recording material in hologram is placed such that reference beam and object beam approach it from two opposite sides, then hologram formed is called Reflection Type hologram. The interference fringes are usually parallel to the surfaces of recording medium. When such a hologram reconstructed, then reference beam and object beam lie on the same side of hologram. Continue reading “Reflection and transmission hologram”

Einstein Coefficient Relation

Einstein Coefficient Relation derivation and discussion:

Einstein showed the interaction of radiation with matter with the help of three processes called stimulated absorption, spontaneous emission and stimulated emission. He showed in 1917 that for proper description of radiation with matter,the process of stimulated emission is essential.Let us first derive the Einstein coefficient relation on the basis of above theory:

Let N1 be the number of atoms per unit volume in the ground state E1 and these atoms exist in the radiation field of photons of energy E2-E1 =h v such that energy density of the field is E. Continue reading “Einstein Coefficient Relation”

How does a laser work

One must have seen and if not seen then must have heard the term laser. But if you have seen the laser light emitting from a source, then there should be natural question how does a laser work? Therefore let us discuss how the laser works?

As already discussed in my earlier articles, that the full form of laser is “Light amplification by stimulated emission of radiation”. Therefore it means that in laser light is amplified through a process called stimulated emission. Thus it means that stimulated emission is that process through which laser can be achieved. That is the reason the stimulated emission is known as the principle of laser.

Concepts to learn how does a laser work: Continue reading “How does a laser work”

Difference beween holography and photography

Last time I have discussed about the holography and written that it is a two stage process. The first stage is recording of hologram in the form of interference pattern and in the second stage, the hologram acts as a diffraction grating for the reconstruction beam and the image of the object is reconstructed for the  hologram.

Do you know what is the difference between hologram and photograph? If no, then let us discuss:

Difference between Holography and Photography Continue reading “Difference beween holography and photography”

Recording and reconstruction process in holography

Last time I have discussed the basic definition of holography and hologram. Today I will discuss the process with the help of which hologram is formed or complete picture is recorded:

1. Recording  of hologram. The recording of hologram  is based on the  phenomenon of interference.  It requires a laser source, a plane  mirror or beam splitter, an object and a photographic plate. A laser beam from the laser source is incident on a plane mirror or beam splitter. As the name suggests, the function of the beam splitter is to split the laser beam. One part of splitted beam, after reflection from the beam splitter, strikes on the photographic plate. This  beam is called reference beam. Continue reading “Recording and reconstruction process in holography”

Holography

The word holography originates from the Greek  words “holos” (complete) and “graphos” (writing). Thus, it is the technique to record the complete picture of an object. The technique was  proposed by Gabor in 1947.

An ordinary photograph records the two dimensional image of the picture because it records only the amplitude or intensity distribution. But in holography technique, both, the intensity as well as phase of the light wave is recorded.

In holography, the light  waves reflected from an object is  recorded. These light  waves  consist of intensity and phase  and the record is called a hologram. The hologram has no resemblance to the original object but it contains all the information about the object in a optical  code. Continue reading “Holography”

Applications of lasers

Lasers have applications in almost every field like medicine, industry, communication and science and technology. These applications are due to the directional, coherent and monochromatic properties of lasers.

a) Holography: Holography is a technique to record the complete picture of an object, that is it will produce the three dimensional picture. The process of holography will be discussed in detail later on.

b) Measurement of long distance: The beam spreading in the laser light is very small, laser can travel along distances, without appreciable spreading. The time taken by laser pulse to  travel from laser source to a given target and back is measured. As the velocity of light is known, the distance of the target can be calculated using the relation 2d =  c x  t where d is the distance of the target and c is the velocity of light. Continue reading “Applications of lasers”

Electro-optical shutters technique in q switching

In my earlier articles I have discussed the basics of Q-switching and three of its techniques known as mechanical shutters, rotating reflector method and passive shutters. Toady I will discuss the one more following techniques of Q-switching:

Electro-optical Shutters.

To obtain faster switching, the suitable electro-optical effects of altering the refractive index of a cell by applying an electic field is used. Two such effects are:

i)   Pockels effect

ii)  Kerr effect

i) Pockels effect. Continue reading “Electro-optical shutters technique in q switching”

Q-switching: The rotating reflector and passive shutters techniques

Last time I have discussed the basics of Q-switching and one of its techniques known as mechanical shutters. Toady I will discuss two more following techniques of Q-switching:

The rotating reflector method.

In this method of Q- switching, one of the  end mirrors of the cavity is replaced with a total reflection prism which  spins rapidly around its axis set at right angle to the resonator axis. As the prism revolves, it  faces the cavity with its reflecting  side and makes the laser cavity quality  factor Q high for a short time. When  the prism is out  of  this  position, the Q value drops. As it revolves on further rotation, Q value drops to minimum. Continue reading “Q-switching: The rotating reflector and passive shutters techniques”