A laser is constructed from three principal parts:
- An energy source (usually referred to as the pump or pump source),
- A gain medium or laser medium, and.
- Two or more mirrors that form an optical resonator.
So, what is meant by lasing action?
In semiconductor lasers, both mirrors often transmit a beam, the second one being used for monitoring purposes. Laser Action. The combination of spontaneous emission first, and then stimulated emission, causes the laser to "lase," which means it generates a coherent beam of light at a single frequency.
What is threshold condition for lasing?
The lasing threshold is the lowest excitation level at which a laser's output is dominated by stimulated emission rather than by spontaneous emission. Below the threshold, the laser's output power rises slowly with increasing excitation.
In laser physics, gain or amplification is a process where the medium transfers part of its energy to the emitted electromagnetic radiation, resulting in an increase in optical power. This is the basic principle of all lasers. Quantitatively, gain is a measure of the ability of a laser medium to increase optical power.
If the photon is having very less frequency (say v=1Hz) ,then the Engery of such photon will be the smallest one. It can be infered that the smallest unit of light energy will correspond to the smallest frequency of such quanta. But from the uncertainity principle it limits the energy of a quanta.
Laser radiation has the following important characteristics over ordinary light source. They are: i) monochromaticity, ii) directionality, iii) coherence and iv) brightness. (i) Monochromaticity: A laser beam is more or less in single wavelength. i.e., the line width of laser beams are extremely narrow.
Coherence is one of the unique properties of laser light. It arises from the stimulated emission process which provides the amplification. Since a common stimulus triggers the emission events which provide the amplified light, the emitted photons are "in step" and have a definite phase relation to each other.
Ultraviolet radiation for lasers consists of wavelengths between 180 and 400 nm. The visible region consists of radiation with wavelengths between 400 and 700 nm. This is the portion we call visible light. The infrared region of the spectrum consists of radiation with wavelengths between 700 nm and 1 mm.
“Laser” is an acronym for light amplification by stimulated emission of radiation. A laser is created when the electrons in atoms in special glasses, crystals, or gases absorb energy from an electrical current or another laser and become “excited.” First, its light contains only one wavelength (one specific color).
At wavelengths shorter than 380nm, optical radiation is termed ultraviolet (UV) and is also invisible to the eye. The term "laser light" refers to a much broader range of the electromagnetic spectrum that just the visible spectrum, anything between 150nm up to 11000nm (i.e. from the UV up to the far IR).
An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light.
Optical pumping is a process in which light is used to raise (or "pump") electrons from a lower energy level in an atom or molecule to a higher one. It is commonly used in laser construction, to pump the active laser medium so as to achieve population inversion.
A longitudinal mode of a resonant cavity is a particular standing wave pattern formed by waves confined in the cavity. The longitudinal modes correspond to the wavelengths of the wave which are reinforced by constructive interference after many reflections from the cavity's reflecting surfaces.
A microwave cavity or radio frequency (RF) cavity is a special type of resonator, consisting of a closed (or largely closed) metal structure that confines electromagnetic fields in the microwave region of the spectrum. At the cavity's resonant frequencies they reinforce to form standing waves in the cavity.
Mode-locking is a technique in optics by which a laser can be made to produce pulses of light of extremely short duration, on the order of picoseconds (10−12 s) or femtoseconds (10−15 s). The basis of the technique is to induce a fixed-phase relationship between the longitudinal modes of the laser's resonant cavity.
Transverse electromagnetic (TEM) modes: neither electric nor magnetic field in the direction of propagation. Transverse electric (TE) modes: no electric field in the direction of propagation. Transverse magnetic (TM) modes: no magnetic field in the direction of propagation.
The dominant mode in a particular waveguide is the mode having the lowest cutoff frequency. For rectangular waveguide this is the TE10 mode. The TE (transverse electric) signifies that all electric fields are transverse to the direction of propagation and that no longitudinal electric field is present.
Transverse electromagnetic (TEM) is a mode of propagation where the electric and magnetic field lines are all restricted to directions normal (transverse) to the direction of propagation. Plane waves are TEM, however, we are more interested in what types of transmission lines can support TEM.
dominant mode: In a waveguide that can support more than one propagation mode, the mode that propagates with the minimum degradation, i.e. , the mode with the lowest cutoff frequency. (188) Note: Designations for the dominant mode are TE10 for rectangular waveguides and TE11 for circular waveguides.
There are different types of waveguides for each type of wave. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves. The geometry of a waveguide reflects its function.
Wave travel along a standard, two-conductor transmission line is of the TEM (Transverse Electric and Magnetic) mode, where both fields are oriented perpendicular to the direction of travel. TEM mode is only possible with two conductors and cannot exist in a waveguide.