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Frequency-resolved Optical Gating
Frequency-resolved optical gating (FROG) is a general method for measuring the Spectral density, spectral phase of Ultrashort pulse, ultrashort laser pulses, which range from subfemtosecond to about a nanosecond in length. Invented in 1991 by Rick Trebino and Daniel J. Kane, FROG was the first technique to solve this problem, which is difficult because, ordinarily, to measure an event in time, a shorter event is required with which to measure it. For example, to measure a soap bubble popping requires a strobe light with a shorter duration to freeze the action. Because ultrashort laser pulses are the shortest events ever created, before FROG, it was thought by many that their complete measurement in time was not possible. FROG, however, solved the problem by measuring an "auto-spectrogram" of the pulse, in which the pulse gates itself in a nonlinear optical medium and the resulting gated piece of the pulse is then spectrally resolved as a function of the delay between the two pulse ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Density
In signal processing, the power spectrum S_(f) of a continuous time signal x(t) describes the distribution of power into frequency components f composing that signal. According to Fourier analysis, any physical signal can be decomposed into a number of discrete frequencies, or a spectrum of frequencies over a continuous range. The statistical average of any sort of signal (including noise) as analyzed in terms of its frequency content, is called its spectrum. When the energy of the signal is concentrated around a finite time interval, especially if its total energy is finite, one may compute the energy spectral density. More commonly used is the power spectral density (PSD, or simply power spectrum), which applies to signals existing over ''all'' time, or over a time period large enough (especially in relation to the duration of a measurement) that it could as well have been over an infinite time interval. The PSD then refers to the spectral energy distribution that would be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cross-correlation
In signal processing, cross-correlation is a measure of similarity of two series as a function of the displacement of one relative to the other. This is also known as a ''sliding dot product'' or ''sliding inner-product''. It is commonly used for searching a long signal for a shorter, known feature. It has applications in pattern recognition, single particle analysis, electron tomography, averaging, cryptanalysis, and neurophysiology. The cross-correlation is similar in nature to the convolution of two functions. In an autocorrelation, which is the cross-correlation of a signal with itself, there will always be a peak at a lag of zero, and its size will be the signal energy. In probability and statistics, the term ''cross-correlations'' refers to the correlations between the entries of two random vectors \mathbf and \mathbf, while the ''correlations'' of a random vector \mathbf are the correlations between the entries of \mathbf itself, those forming the correlation mat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nonlinear Optics
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in Nonlinearity, nonlinear media, that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typically observed only at very high light intensities (when the electric field of the light is >108 V/m and thus comparable to the atomic electric field of ~1011 V/m) such as those provided by lasers. Above the Schwinger limit, the vacuum itself is expected to become nonlinear. In nonlinear optics, the superposition principle no longer holds. History The first nonlinear optical effect to be predicted was two-photon absorption, by Maria Goeppert Mayer for her PhD in 1931, but it remained an unexplored theoretical curiosity until 1961 and the almost simultaneous observation of two-photon absorption at Bell Labs and the discovery of second-harmonic generation by Peter Franken ''et al.'' at University of Michigan, both shortly after th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Review Of Scientific Instruments
''Review of Scientific Instruments'' is a monthly peer-reviewed scientific journal published by the American Institute of Physics. Its area of interest is scientific instruments, apparatus, and techniques. According to the ''Journal Citation Reports'', the journal has a 2018 impact factor The impact factor (IF) or journal impact factor (JIF) of an academic journal is a type of journal ranking. Journals with higher impact factor values are considered more prestigious or important within their field. The Impact Factor of a journa ... of 1.587. Editors * 2024-Present: Réjean Boivin * 2024: Robert Kaita (Interim Editor in Chief) * 2016-2023: Richard C. Pardo * 2000-2015: Albert T. Macrander * 1979-1999: Thomas H. Braid * 1954-1978: J. B. Horner Kuper * 1940-1954: Gaylord P. Harnwell * 1940: Joseph A. Becker * 1932-1939: F. K. Richtmyer * 1930-1932: Paul D. Foote References External links * Chemistry journals Physics journals Research methods journals American Institute ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiphoton Intrapulse Interference Phase Scan
Multiphoton intrapulse interference phase scan (MIIPS) is a method used in ultrashort laser technology that simultaneously measures (phase characterization), and compensates (phase correction) femtosecond laser pulses using an adaptive pulse shaper. When an ultrashort laser pulse reaches a duration of less than a few hundred femtosecond, it becomes critical to characterize its duration, its temporal intensity curve, or its electric field as a function of time. Classical photodetectors measuring the intensity of light are still too slow to allow for a direct measurement, even with the fastest photodiodes or streak cameras. Other means have been developed based on quasi instantaneous non linear optical effects such as autocorrelation, FROG, SPIDER, etc. However, these can only measure the pulse characteristics but not correct for defects in order to make the pulse as short as possible. For instance, the pulse could be linearly chirped or present higher order group delay dispersion ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spectral Phase Interferometry For Direct Electric-field Reconstruction
In ultrafast optics, spectral phase interferometry for direct electric-field reconstruction (SPIDER) is an ultrashort pulse measurement technique originally developed by Chris Iaconis and Ian Walmsley. The basics SPIDER is an interferometric ultrashort pulse measurement technique in the frequency domain based on shearing interferometer, spectral shearing interferometry. Spectral shearing interferometry is similar in concept to lateral shearing interferometry, except the shearing is performed in the frequency domain. The spectral shear is typically generated by sum-frequency mixing the test pulse with two different quasi-monochromatic frequencies (usually derived by chirping a copy of the pulse itself), although it can also be achieved by spectral filtering or even with linear electro-optic modulators for picosecond pulses. The interference between the two upconverted pulses allows the spectral phase at one frequency to be referenced to the spectral phase at a different frequency, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Double-Blind FROG
Double-blind frequency-resolved optical gating (double-blind FROG) is a method for simultaneously measuring two unknown ultrashort laser pulses. Well established ultrafast measurement techniques such as frequency-resolved optical gating Frequency-resolved optical gating (FROG) is a general method for measuring the Spectral density, spectral phase of Ultrashort pulse, ultrashort laser pulses, which range from subfemtosecond to about a nanosecond in length. Invented in 1991 by Rick ... and its simplified version GRENOUILLE can only measure one unknown ultrashort laser pulse at a time. Another version of FROG, called cross-correlation FROG (XFROG), also measures only one pulse, but it involves two pulses: a known reference pulse and the unknown pulse to be measured. In modern optics experiments, ultrashort laser pulses have been used in a great variety of engineering application and scientific research, for example, biomedical engineering, material science, nonlinear spectroscopy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Grating-eliminated No-nonsense Observation Of Ultrafast Incident Laser Light E-fields
Grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields (GRENOUILLE) is an ultrashort pulse measurement technique based on frequency-resolved optical gating (FROG). The acronym was chosen because of the technique's relationship to FROG; ''grenouille'' is French for ''frog''. Theory Because most FROG techniques have an autocorrelator, they also have the sensitive alignment issues that come with it. In addition, most FROGs use a thin second-harmonic generation (SHG) crystal and a spectrometer, adding signal strength requirements as well as additional alignment issues. GRENOUILLE is a simple device based on the SHG FROG, replacing the beam splitter, delay line and beam recombination components of the autocorrelator with a prism, and replacing the spectrometer and thin SHG crystal combination with a thick SHG crystal. The effect of these replacements is to eliminate all sensitive alignment parameters while increasing the signal strength. These changes al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Overdetermined System
In mathematics, a system of equations is considered overdetermined if there are more equations than unknowns. An overdetermined system is almost always inconsistent equations, inconsistent (it has no solution) when constructed with random coefficients. However, an overdetermined system will have solutions in some cases, for example if some equation occurs several times in the system, or if some equations are linear combinations of the others. The terminology can be described in terms of the concept of constraint counting. Each Variable (mathematics), unknown can be seen as an available degree of freedom. Each equation introduced into the system can be viewed as a constraint (mathematics), constraint that restricts one degree of freedom. Therefore, the critical case occurs when the number of equations and the number of free variables are equal. For every variable giving a degree of freedom, there exists a corresponding constraint. The ''overdetermined'' case occurs when the syste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Second-harmonic Generation
Second-harmonic generation (SHG), also known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. As a prototype behavior of waves, SHG is widely used, for example, in doubling laser frequencies. SHG was initially discovered as a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy of the initial photons (equivalently, twice the frequency and half the wavelength), that conserves the coherence of the excitation. It is a special case of sum-frequency generation (2 photons), and more generally of harmonic generation. The second-order nonlinear susceptibility of a medium characterizes its tendency to cause SHG. Second-harmonic generation, like other even-order nonlinear optical phenomena, is not allowed in media with inversion symmet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffraction Grating
In optics, a diffraction grating is an optical grating with a periodic structure that diffraction, diffracts light, or another type of electromagnetic radiation, into several beams traveling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structural coloration. The directions or diffraction angles of these beams depend on the wave (light) Angle of incidence (optics), incident angle to the diffraction grating, the spacing or periodic distance between adjacent diffracting elements (e.g., parallel slits for a transmission grating) on the grating, and the wavelength of the incident light. The grating acts as a dispersion (optics), dispersive element. Because of this, diffraction gratings are commonly used in monochromators and spectrometers, but other applications are also possible such as optical encoders for high-precision motion control and wavefront measurement. For typical applications, a reflection (optics), reflective grati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
