Far-infrared laser or terahertz laser (FIR laser, THz laser) is a

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fi ...

with output

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, t ...

in between 30-1000 µm (

frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

0.3-10 THz), in the

far infrared Far infrared (FIR) is a region in the infrared spectrum of electromagnetic radiation. Far infrared is often defined as any radiation with a wavelength of 15 micrometers (μm) to 1 mm (corresponding to a range of about 20 THz to ...

or terahertz

frequency band A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum. The frequency range of a system is the range over which i ...

of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...

. FIR lasers have application in terahertz spectroscopy,

terahertz imaging Terahertz nondestructive evaluation pertains to devices, and techniques of analysis occurring in the terahertz domain of electromagnetic radiation. These devices and techniques evaluate the properties of a material, component or system without cau ...

as well in fusion plasma physics diagnostics. They can be used to detect explosives and

chemical warfare agent A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as a ...

s, by the means of

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...

or to evaluate the plasma densities by the means of interferometry techniques. FIR lasers typically consist of a long (1–3 meters)

waveguide A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities de ...

filled with gaseous organic molecules, optically pumped or via HV discharge. They are highly inefficient, often require helium cooling, high magnetic fields, and/or are only line tunable. Efforts to develop smaller solid-state alternatives are under way. The p-Ge (p-type germanium) laser is a tunable, solid state, far infrared laser which has existed for over 25 years. It operates in crossed electric and magnetic fields at liquid helium temperatures. Wavelength selection can be achieved by changing the applied electric/magnetic fields or through the introduction of intracavity elements.

Quantum cascade laser Quantum-cascade lasers (QCLs) are semiconductor lasers that emit in the mid- to far-infrared portion of the electromagnetic spectrum and were first demonstrated by Jérôme Faist, Federico Capasso, Deborah Sivco, Carlo Sirtori, Albert Hutchinson, ...

(QCL) is a construction of such alternative. It is a solid-state

semiconductor laser The laser diode chip removed and placed on the eye of a needle for scale A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...

that can operate continuously with output power of over 100 mW and wavelength of 9.5 µm. A prototype was already demonstrated. and potential use shown. A molecular FIR laser optically pumped by a QCL has been demonstrated in 2016. It operates at room-temperature and is smaller than molecular FIR lasers optically pumped by CO₂ lasers.

Free electron laser A free-electron laser (FEL) is a (fourth generation) light source producing extremely brilliant and short pulses of radiation. An FEL functions and behaves in many ways like a laser, but instead of using stimulated emission from atomic or molecula ...

s can also operate on far infrared wavelengths. Femtosecond Ti:sapphire mode-locked lasers are also being used to generate very short pulses that can be optically rectified to produce a terahertz pulse.

References

Terahertz technology Laser types {{electronics-stub

See also

References