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In optics, an ultrashort pulse of light is an electromagnetic pulse whose time duration is on the order of the femtosecond (10 − 15 second). The term electromagnetic pulse ( EMP) has the following meanings Electromagnetic radiation from an Explosion (especially a Nuclear Such pulses have a broadband optical spectrum, and can be created by mode-locked oscillators. 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 (10-12s They are commonly referred to as ultrafast events. In Optics, an ultrashort pulse of light is an Electromagnetic pulse whose time duration is on the order of the femtosecond (10^{-15} second

They are characterized by a high peak intensity (or more correctly, irradiance) that usually leads to nonlinear interactions in various materials, including air. In Physics, intensity is a measure of the time-averaged Energy Flux. Irradiance, radiant emittance, and radiant exitance are Radiometry terms for the power of Electromagnetic radiation at a surface per unit These processes are studied in the field of nonlinear optics. Nonlinear optics (NLO is the branch of Optics that describes the behaviour of Light in nonlinear media, that is media in which the dielectric polarization

In the specialized literature, "ultrashort" refers to the femtosecond (fs) to picosecond (ps) range, although such pulses no longer hold the record for the shortest pulses artificially generated. Indeed, pulse durations on the attosecond time scale have been reported. To compare various Orders of magnitude of Time units this page lists units of time between 10&minus18 and 10&minus15 seconds (i

The 1999 Nobel Prize in Chemistry was awarded to Ahmed H. Zewail for using ultrashort pulses to observe chemical reactions on the timescales they occur on, opening up the field of femtochemistry. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) The Nobel Prize in Chemistry (Nobelpriset i kemi is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of Chemistry. Ahmed Hassan Zewail (أحمد حسن زويل (born February 26 1946 in Damanhur, Egypt) is an Egyptian American scientist and the A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Femtochemistry is the Science that studies Chemical reactions on extremely short timescales approximately 10–15 seconds (one Femtosecond

Contents

Definition

An ultrashort pulse of light in the time domain. In this figure, the amplitude and intensity are Gaussian functions. The phase function is quadratic, resulting in an instantaneous frequency sweep sometimes called chirp, in analogy to the sound of some birds.
An ultrashort pulse of light in the time domain. In this figure, the amplitude and intensity are Gaussian functions. In Mathematics, a Gaussian function (named after Carl Friedrich Gauss) is a function of the form f(x = a e^{- { (x-b^2 \over 2 The phase function is quadratic, resulting in an instantaneous frequency sweep sometimes called chirp, in analogy to the sound of some birds. A chirp is a signal in which the Frequency increases ('up-chirp' or decreases ('down-chirp' with time Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs.

The real electric field corresponding to an ultrashort pulse is oscillating at an angular frequency ω0 corresponding to the central wavelength of the pulse. To facilitate calculations, a complex field E(t) is defined. Formally, it is defined as the analytic signal corresponding to the real field. In Mathematics and Signal processing, the analytic representation of a real-valued function or signal facilitates many mathematical manipulations of the signal

The central angular frequency ω0 is usually explicitly written in the complex field, which may be separated as an intensity function I(t) and a phase function ψ(t):

E(t) = \sqrt{I(t)}e^{i\omega_0t}e^{i\psi(t)}

The expression of the complex electric field in the frequency domain is obtained from the Fourier transform of E(t):

E(\omega) = \mathcal{F}(E(t))

Because of the presence of the e^{i\omega_0t} term, E(ω) is centered around ω0, and it is a common practice to refer to E(ω-ω0) by writing just E(ω), which we will do in the rest of this article. This article specifically discusses Fourier transformation of functions on the Real line; for other kinds of Fourier transformation see Fourier analysis and

Just as in the time domain, an intensity and a phase function can be defined in the frequency domain:

E(\omega) = \sqrt{S(\omega)}e^{i\phi(\omega)}

The quantity S(ω) is the spectral density (or simply, the spectrum) of the pulse, and φ(ω) is the spectral phase. Example of spectral phase functions include the case where φ(ω) is a constant, in which case the pulse is called a bandwidth-limited pulse, or where φ(ω) is a quadratic function, in which case the pulse is called a chirped pulse because of the presence of an instantaneous frequency sweep. A bandwidth-limited pulse (also known as Fourier-transform-limited pulse, or more commonly transform-limited pulse) is a Pulse of a Wave that A chirp is a signal in which the Frequency increases ('up-chirp' or decreases ('down-chirp' with time Such a chirp may be acquired as a pulse propagates through materials (like glass) and is due to their dispersion. It results in a temporal broadening of the pulse.

The intensity functions I(t) and S(ω) determine the time duration and spectral bandwidth of the pulse. As stated by the uncertainty principle, their product (sometimes called the time-bandwidth product) has a lower bound. In Quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the Momentum of the particle uncertain This minimum value depends on the definition used for the duration and on the shape of the pulse. For a given spectrum, the minimum time-bandwidth product, and therefore the shortest pulse, is obtained by a transform-limited pulse, i. e. , for a constant spectral phase φ(ω). High values of the time-bandwidth product, on the other hand, indicate a more complex pulse.

Pulse shape control

Although optical devices also used for continuous light, like beam expanders and spatial filters, may be used for ultrashort pulses, several optical devices have been specifically designed for ultrashort pulses. One of them is the pulse compressor, a device that can be used to control the spectral phase of ultrashort pulses. A prism compressor is an optical device used to shorten the duration of a positively chirped ultrashort laser pulse by giving different Wavelength It is composed of a sequence of prisms, or gratings. When properly adjusted it can alter the spectral phase φ(ω) of the input pulse so that the output pulse is a bandwidth-limited pulse with the shortest possible duration. A bandwidth-limited pulse (also known as Fourier-transform-limited pulse, or more commonly transform-limited pulse) is a Pulse of a Wave that A pulse shaper can be used to make more complicated alterations on both the phase and the amplitude of ultrashort pulses. In Optics, Femtosecond pulse shaping refers to various techniques to modify the temporal profile of an Ultrashort pulse from a laser

To accurately control the pulse, a full characterization of the pulse spectral phase is a must in order to get certain pulse spectral phase (such as Transform-Limited). A bandwidth-limited pulse (also known as Fourier-transform-limited pulse, or more commonly transform-limited pulse) is a Pulse of a Wave that Then, a Spatial light modulator can be used in the 4f plane to control the pulse. A spatial light modulator (SLM is an object that imposes some form of spatially-varying Modulation on a beam of light Multiphoton Intrapulse Interference Phase Scan (MIIPS) is a technque based on this concept. Multiphoton intrapulse interference phase scan ( MIIPS) is a method used in ultrashort laser technology that simultaneously measures (phase characterization Through the phase scan of the spatial light modulator, MIIPS can not only characterize but also manipulate the ultrashort pulse to get the needed pulse shape at target spot (such as transform-limited pulse for optimized peak power, and other sepcific pulse shapes). A spatial light modulator (SLM is an object that imposes some form of spatially-varying Modulation on a beam of light A bandwidth-limited pulse (also known as Fourier-transform-limited pulse, or more commonly transform-limited pulse) is a Pulse of a Wave that This technique features with full calibration and control of the ultrashort pulse, with no moving parts, and simple optical setup.

Measurement techniques

Several techniques are available to measure ultrashort optical pulses:

Methods of characterizing and controlling the ultrashort optical pulses:

Applications of ultrashort pulses

External links

References

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