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The coherence time, usually designated τ, is calculated by dividing the coherence length by the phase velocity of light in a medium; approximately given by = where λ is the central wavelength of the source, Δν and Δλ is the spectral width of the source in units of frequency and wavelength respectively, and c is the speed of light in vacuum.
A mode-locked laser is capable of emitting extremely short pulses on the order of tens of picoseconds down to less than 10 femtoseconds.These pulses will repeat at the round trip time, that is, the time that it takes light to complete one round trip between the mirrors comprising the resonator.
FROG is simply a spectrally resolved autocorrelation, which allows the use of a phase-retrieval algorithm to retrieve the precise pulse intensity and phase vs. time. It can measure both very simple and very complex ultrashort laser pulses, and it has measured the most complex pulse ever measured without the use of a reference pulse.
The optimal parameters are 4 degrees of noncollinearity, β-barium borate (BBO) as the material, a 400-nm pump wavelength, and signal around 800 nm (and can be tunable in the range 605-750 nm with sub-10 fs pulse width which allows exploring the ultrafast dynamics of large molecules [1]) This generates a bandwidth 3 times as large of that of a ...
There are two closely related measures. The pulse repetition interval measures the time between the leading edges of two pulses but is normally expressed as the pulse repetition frequency (PRF), the number of pulses in a given time, typically a second. The duty cycle expresses the pulse width as a fraction or percentage of one complete cycle.
The experimental setup is adjusted to detect 1 photon per 100 excitation pulses. In other words, less than one emitted photon is detected per laser pulse, and the process is repeated multiple times to get an average value. It measures the time difference between the excitation pulse and the photon detection, also called the time width (Δt).
A frequency comb or spectral comb is a spectrum made of discrete and regularly spaced spectral lines.In optics, a frequency comb can be generated by certain laser sources.. A number of mechanisms exist for obtaining an optical frequency comb, including periodic modulation (in amplitude and/or phase) of a continuous-wave laser, four-wave mixing in nonlinear media, or stabilization of the pulse ...
Using this equation, the minimum pulse duration can be calculated consistent with the measured laser spectral width. For the HeNe laser with a 1.5 GHz bandwidth, the shortest Gaussian pulse consistent with this spectral width is around 300 picoseconds; for the 128 THz bandwidth Ti:sapphire laser, this spectral width corresponds to a pulse of ...