Churn, Learn & Earn
Physics
Einstein Coefficient Relation
Mar 13th
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. More >
How does a laser work
Jan 18th
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: More >
Difference beween holography and photography
May 30th
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 More >
Recording and reconstruction process in holography
May 30th
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. More >
Holography
May 30th
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. More >
Applications of lasers
May 29th
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. More >
Electro-optical shutters technique in q switching
May 27th
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. More >
Q-switching: The rotating reflector and passive shutters techniques
May 27th
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. More >
Q Switching
May 23rd
Q-switching is a technique used to produce a high output pulse. It is accomplished by using a device to prevent the reflection of photons back and forth in the active medium. This produces a higher population inversion in the metastable state. Then suddenly the optical cavity is opened to permit a large fraction of stored energy to be emitted in the form of very intense pulse of laser radiation. Q-switched lasers produce pulses of 10 to 250 nanoseconds.
Q-switching is also known as Q-spoiling.
As the quality factor Q of a laser cavity shows the ability of the cavity to store energy, thus, high Q means that high energy can be stored in the cavity and a low Q means that the cavity will rapidly dissipate its energy. As the technique of Q-switching involves switching the optical cavity quality factor Q from a low to a high value, therefore, it is known as Q-switching.
Techniques of the Q-Switching : More >
Ouput and applications of dye laser
May 18th
I have already discussed the construction and working of dye laser. Let us discuss the output and applications of dye lasers.
Output: The dye laser provides 3nsec pulses in the spectral range of 360 nm to 950 nm. The typical peak powers are on the order of about 10kW to 20kW. Dye lasers can be operated in both pulsed and continue wave (CW) modes. If a flash lamp is used to pump the dye laser, the output will be pulsed one whereas if the laser is pumped by a continuous wave laser like argon-ion laser, the dye laser will also be continuous. More >