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The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency or wavelength. The spectrum is divided into separate bands, with different names for the electromagnetic waves within each band. From low to high frequency these are: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. The electromagnetic waves in each of these bands have different characteristics, such as how they are produced, how they interact with matter, and their practical applications.
The hertz is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event per second. The hertz is an SI derived unit whose formal expression in terms of SI base units is s−1, meaning that one hertz is one per second or the reciprocal of one second. It is used only in the case of periodic events. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. For high frequencies, the unit is commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz).
The second is a unit of time, historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.
A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, 1/1000000000 of a second, or 10−9 seconds.
A millisecond is a unit of time in the International System of Units equal to one thousandth of a second or 1000 microseconds.
A microsecond is a unit of time in the International System of Units (SI) equal to one millionth of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available.
In chemistry, hydronium is the cation [H3O]+, also written as H3O+, the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid is dissolved in water, as Arrhenius acid molecules in solution give up a proton to the surrounding water molecules. In fact, acids must be surrounded by more than a single water molecule in order to ionize, yielding aqueous H+ and conjugate base.
A femtosecond is a unit of time in the International System of Units (SI) equal to 10−15 or 1⁄1 000 000 000 000 000 of a second; that is, one quadrillionth, or one millionth of one billionth, of a second.
Nano is a unit prefix meaning one billionth. Used primarily with the metric system, this prefix denotes a factor of 10−9 or 0.000000001. It is frequently encountered in science and electronics for prefixing units of time and length.
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). A laser operated in this way is sometimes referred to as a femtosecond laser, for example, in modern refractive surgery. The basis of the technique is to induce a fixed phase relationship between the longitudinal modes of the laser's resonant cavity. Constructive interference between these modes can cause the laser light to be produced as a train of pulses. The laser is then said to be "phase-locked" or "mode-locked".
Terahertz radiation – also known as submillimeter radiation, terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, T-lux or THz – consists of electromagnetic waves within the International Telecommunication Union-designated band of frequencies from 0.3 to 3 terahertz (THz), although the upper boundary is somewhat arbitrary and is considered by some sources as 30 THz. One terahertz is 1012 Hz or 1,000 GHz. Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm = 100 μm. Because terahertz radiation begins at a wavelength of around 1 millimeter and proceeds into shorter wavelengths, it is sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared, and can be regarded as either.
In physics and physical chemistry, time-resolved spectroscopy is the study of dynamic processes in materials or chemical compounds by means of spectroscopic techniques. Most often, processes are studied after the illumination of a material occurs, but in principle, the technique can be applied to any process that leads to a change in properties of a material. With the help of pulsed lasers, it is possible to study processes that occur on time scales as short as 10−16 seconds. All time-resolved spectra are suitable to be analyzed using the two-dimensional correlation method for a correlation map between the peaks.
In electronics, rapid single flux quantum (RSFQ) is a digital electronic device that uses superconducting devices, namely Josephson junctions, to process digital signals. In RSFQ logic, information is stored in the form of magnetic flux quanta and transferred in the form of Single Flux Quantum (SFQ) voltage pulses. RSFQ is one family of superconducting or SFQ logic. Others include Reciprocal Quantum Logic (RQL), ERSFQ – energy-efficient RSFQ version that does not use bias resistors, etc. Josephson junctions are the active elements for RSFQ electronics, just as transistors are the active elements for semiconductor electronics. RSFQ is a classical digital, not quantum computing, technology.
In physics, terahertz time-domain spectroscopy (THz-TDS) is a spectroscopic technique in which the properties of matter are probed with short pulses of terahertz radiation. The generation and detection scheme is sensitive to the sample's effect on both the amplitude and the phase of the terahertz radiation.
Photomixing is the generation of continuous wave terahertz radiation from two lasers. The beams are mixed together and focused onto a photomixer device which generates the terahertz radiation. It is technologically significant because there are few sources capable of providing radiation in this waveband, others include frequency multiplied electronic/microwave sources, quantum cascade laser and ultrashort pulsed lasers with photoconductive switches as used in terahertz time-domain spectroscopy. The advantages of this technique are that it is continuously tunable over the frequency range from 300 GHz to 3 THz, and spectral resolutions in the order of 1 MHz can be achieved. However, the achievable power is on the order of 10−8 W.
Terahertz tomography is a class of tomography where sectional imaging is done by terahertz radiation. Terahertz radiation is electromagnetic radiation with a frequency between 0.1 and 10 THz; it falls between radio waves and light waves on the spectrum; it encompasses portions of the millimeter waves and infrared wavelengths. Because of its high frequency and short wavelength, terahertz wave has a high signal-to-noise ratio in the time domain spectrum. Tomography using terahertz radiation can image samples that are opaque in the visible and near-infrared regions of the spectrum. Terahertz wave three-dimensional (3D) imaging technology has developed rapidly since its first successful application in 1997, and a series of new 3D imaging technologies have been proposed successively.
Rotational correlation time is the average time it takes for a molecule to rotate one radian. In solution, rotational correlation times are in the order of picoseconds. For example, the 1.7 ps for water, and 100 ps for a pyrroline nitroxyl radical in a DMSO-water mixture. Rotational correlation times are employed in the measurement of microviscosity and in protein characterization.
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 causing damage.
Terahertz spectroscopy detects and controls properties of matter with electromagnetic fields that are in the frequency range between a few hundred gigahertz and several terahertz. In many-body systems, several of the relevant states have an energy difference that matches with the energy of a THz photon. Therefore, THz spectroscopy provides a particularly powerful method in resolving and controlling individual transitions between different many-body states. By doing this, one gains new insights about many-body quantum kinetics and how that can be utilized in developing new technologies that are optimized up to the elementary quantum level.
Anisotropic terahertz microspectroscopy (ATM) is a spectroscopic technique in which molecular vibrations in an anisotropic material are probed with short pulses of terahertz radiation whose electric field is linearly polarized parallel to the surface of the material. The technique has been demonstrated in studies involving single crystal sucrose, fructose, oxalic acid, and molecular protein crystals in which the spatial orientation of molecular vibrations are of interest.
References
- ↑ "Trillion-frame-per-second video". Massachusetts Institute of Technology. Retrieved 2014-03-06.
- ↑ "Ultra high speed CCD cameras capture the motion of light". Stanford Computer Optics. Retrieved 2014-03-06.
- ↑ "Lifetime of single hydronium (H3O+) ion at 20°C". BioNumbers. Retrieved 2011-10-10.
- ↑ James E. Kloeppel (2006-12-11). "World's Fastest Transistor Approaches Goal of Terahertz Device".
- ↑ Lankhorst, D.; Schriever, J.; Leyte, J. C. (1982). "Determination of the Rotational Correlation Time of Water by Proton NMR Relaxation in H217O and Some Related Results". Berichte der Bunsengesellschaft für physikalische Chemie. 86 (3): 215–221. doi:10.1002/bbpc.19820860308.
- ↑ SFF Committee. "SFF-8431 Specifications for Enhanced Small Form Factor Pluggable Module SFP+" (PDF).
- ↑ Bulla, I.; Törmälä, P.; Lindberg, J. J.; Mikalsen, Ø.; Southern, J. T.; Edlund, K.; Eliasen, M.; Herskind, C.; Laursen, T.; Pedersen, P. M. L. (1975). "Spin Probe Studies on the Dynamic Structure of Dimethyl Sulfoxide-Water Mixtures". Acta Chemica Scandinavica. 29a: 89–92. doi: 10.3891/acta.chem.scand.29a-0089 .
- ↑ "Universal Serial Bus 3.1 Specification" (PDF).