Multiphoton intrapulse interference phase scan
Other means have been developed based on quasi instantaneous non linear optical effects such as autocorrelation, FROG, SPIDER, etc.
MIIPS can not only measure the pulse but also correct the high-order dispersion, thus is highly preferable for applications where repeatable electromagnetic field is important, such as to generate ultrashort pulses which are transform limited or possess specific phase characteristics.
A MIIPS-based device consists of two basic components controlled by a computer: a pulse shaper (usually a liquid crystal based spatial light modulator - SLM) and a spectrometer.
The spectrometer records the spectrum of a nonlinear optical process such as second harmonic generation produced by the laser pulse.
MIIPS is similar to FROG in that a frequency trace is collected for the characterization of the ultrashort pulse.
In Frequency-resolved optical gating, a FROG trace is collected through scanning the ultrashort pulse across the temporal axis, and detecting the spectrum of the nonlinear process.
, by the pulse shaper to locally cancel distortions by the unknown spectral phase,
The phase modulation procedure of the physical process is generally a continuous function.
The frequency doubled spectrum recorded for each full scan of the reference phase
The system then introduces a correction phase to cancel the distortions and achieve shorter pulses.
The absolute accuracy of MIIPS improves as the phase distortions diminish, therefore an iterative procedure of measurement and compensation is applied to reduce phase distortions below 0.1 radian for all frequencies within the bandwidth of the laser.
When all phase distortions have been eliminated, the pulses have the highest possible peak power, and are considered to be Bandwidth-limited-pulse|transform limited (TL).
The MIIPS trace corresponding to TL pulses shows straight parallel lines separated by
MIIPS technology has been applied successfully in selective excitation of multiphoton imaging and femtosecond light-mass interaction study.
The curved mirror reflects the laser to the spatial light modulator (SLM).
spectra vs. the phase scan can be recorded as a MIIPS trace for the characterization of the pulse.
There is also an improved MIIPS[1] algorithm that allows for efficient phase retrieval in a single iteration, providing that the laser spectrum at the reference sample is known.
This method of analysis avoids a type of non-trivial ambiguity that arises for structured amplitude pulse profiles and can provide better feedback on the accuracy of the phase retrieval.
Gated-MIIPS (G-MIIPS)[2] is an enhanced variant of MIIPS, designed to address the limitations posed by higher-order phase distortions in ultrashort laser pulse characterization.
G-MIIPS employs an amplitude gate scanned across the spectrum, mitigating the influence of higher-order phase terms and enabling efficient compression of broadband laser pulses with a simple 4𝑓 pulse shaper setup.
G-MIIPS is particularly effective for correcting substantial phase distortions caused by factors like high-NA microscope objectives.
