pulse characterization (original) (raw)
Definition: the measurement of various properties of an optical pulse
Categories: 
light detection and characterization, 
optical metrology, 
light pulses
- pulse characterization
- pulse duration measurement
- carrier–envelope frequency measurement
- autocorrelators
- frequency-resolved optical gating
- spectral phase interferometry
- streak cameras
Related: light pulsespulse propertiesspectral phasecarrier–envelope offsetautocorrelatorsfrequency-resolved optical gatingspectral phase interferometrystreak cameras
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DOI: 10.61835/wly Cite the article: BibTex BibLaTex plain textHTML Link to this page! LinkedIn
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Contents
Introduction
Light pulses and regular optical pulse trains can be generated e.g. with Q-switched and mode-locked lasers and often need to be characterized in various respects. As important pulse parameters such as pulse duration and energy and also the aspects of interest can be very different, in the following we separately consider pulse characterization for Q-switched and mode-locked lasers.
Pulse Characterization for Q-switched Lasers
The pulse characterization for Q-switched lasers is relatively simple; it typically comprises the following aspects:
- The pulse duration, which is typically in the nanosecond regime, can be directly measured with a fast photodetector.
- The pulse energy may be measured directly (e.g. with a pyroelectric detector). In some cases with repetitive operation, it is calculated from the average power (from a power meter) and repetition rate. One may also use a properly calibrated photodiode signal.
- The peak power may be directly measured with a fast photodiode or calculated from pulse energy, pulse duration and pulse shape.
- The pulse repetition rate is typically determined by the laser driver and thus does not need to be measured. In the case of passive Q-switching, one may use a photodiode and an oscilloscope or an electronic spectrum analyzer.
- The timing jitter of a Q-switched laser may be substantial. It may be calculated based on measurements with a sufficiently fast photodiode.
- The optical center frequency and spectral shape can be obtained with an optical spectrum analyzer.
Pulse Characterization for Mode-locked Lasers
Basics
- The pulse duration is typically too short for direct measurements even with a very fast photodiode. Therefore, one uses various other methods, e.g. based on an autocorrelator or a streak camera. One may also derive the pulse duration from a complete pulse characterization as explained below. Optical sampling techniques can be used when a shorter reference pulse is available.
- The pulse energy is typically calculated as the average power (from a power meter) divided by the pulse repetition rate.
- The peak power is usually calculated from pulse energy, pulse duration and pulse shape. Note that there may be substantial uncertainties concerning the pulse shape, if no complete pulse characterization is performed.
- The pulse repetition rate (in the megahertz or gigahertz region) is usually measured with a fast photodiode and an electronic spectrum analyzer.
- The optical center frequency and spectral shape can be obtained with an optical spectrum analyzer. In many cases, one does not resolve the lines of the obtained frequency comb, but only obtains the spectral envelope.
Complete Ultrashort Pulse Characterization
The characterization as outlined above is still somewhat incomplete. There are methods of complete pulse characterization [6], which reveal more details:
- the electric field versus time or the complex spectrum (including spectral shape and spectral phase)
- the precise pulse shape
- the chirp of the pulses
For example, an ordinary intensity autocorrelator always delivers symmetric signal shapes concerning time, even if the pulses are asymmetric (e.g. with steep rise and a slower fall of power). The pulse duration calculated from an autocorrelation trace is often based on the assumption of a certain temporal pulse shape, which cannot be fully validated based on the obtained data. Such an autocorrelator can also not reveal any optical phase properties or a chirp.
The most prominent techniques for complete pulse characterization are
- FROG (frequency-resolved optical gating [2]) and
- SPIDER (spectral phase interferometry for direct electric-field reconstruction [9], → spectral phase interferometry).
The results can be visualized in various ways, e.g. with graphs of time- or frequency-dependent functions, or with spectrograms.
Generally, some optical nonlinearities are exploited for characterizing ultrashort pulses. Purely linear optical effects, e.g. interference effects, could give information on the optical spectrum but not on the spectral phase, which is crucial for the temporal pulse shape.
Further possibly interesting details are:
- The carrier–envelope offset frequency of the frequency comb is of special interest in optical metrology, and may be measured with an ($f-2f$) interferometer.
- The timing jitter of a pulse train can be measured with various methods, e.g. with a fast photodiode, a fast sampling card and software, or with more sophisticated methods [17].
- The temporal coherence (e.g. of subsequent pulses) can be characterized e.g. with an interferometer.
Spatial Aspects
Note that apart from the temporal aspect, there is also the spatial aspect [16]. Both aspects are often approximately separated in the sense that the whole spatio-temporal profile of the electric field of a pulse can be specified as the product of two functions, one depending only on time and the other only on the spatial position. However, a significant coupling of temporal and spatial properties can occur in various situations. For example, pulses from Kerr lens mode-locked lasers often exhibit a time-dependent beam radius, which makes the complete characterization (and modeling) very challenging. Another spatio-temporal aspect is pulse front tilt, which is related to angular dispersion and can, e.g., result from a misaligned pulse compressor.
Applications
Accurate and reliable pulse characterization is essential for many applications. For example, if an ultrafast laser system does not work properly, e.g., due to misalignment of components, this can greatly affect the operation of a larger system. The problem can be localized and fixed only if the pulse properties can be monitored. Therefore, an ultrafast laser system can often be considered as complete only if it comprises comprehensive pulse characterization equipment, which may substantially contribute to the overall cost.
Particularly careful pulse characterization may be required in the laser development, where various effects on the pulse formation need to be investigated.
Frequently Asked Questions
This FAQ section was generated with AI based on the article content and has been reviewed by the article’s author (RP).
What is the difference between characterizing Q-switched and mode-locked laser pulses?
How can the duration of nanosecond laser pulses be measured?
Why can't a fast photodiode measure the duration of an ultrashort pulse?
What is 'complete pulse characterization'?
Complete pulse characterization determines not just the pulse duration, but also the precise temporal shape and the spectral phase or chirp. This is necessary because simpler methods, like using an intensity autocorrelator, cannot reveal pulse asymmetries or phase properties.
What are FROG and SPIDER?
What are spatio-temporal effects in pulse characterization?
Spatio-temporal effects are couplings between the spatial and temporal properties of a pulse. Examples include a time-dependent beam radius or a pulse front tilt, which can result from misaligned optics like a pulse compressor.
Suppliers
Sponsored content: The RP Photonics Buyer's Guide contains 29 suppliers for pulse characterization. Among them:
⚙ hardware
The Blueback advanced ultrashort laser pulse characterization device is a real-time ultrashort laser pulse characterization device specifically engineered to provide a high-resolution measurement for ultrafast oscillators and amplifiers. It is an essential piece of equipment for everyone who depends on accurate information about properties of their ultrashort pulses. With Fluence Blueback you get more than just a single result. You can watch your pulse evolving in real time.
⚙ hardware
Femto Easy offers different kinds of devices for the characterization of ultrashort light pulses:
- Single-shot and scanning autocorrelators are easy tools for measuring pulse durations.
- FROG devices allow for full pulse characterization. They are also available in single-shot and scanning versions.
All devices are optimized for easy installation and handling.
⚙ hardware
Ultrafast photodetectors from ALPHALAS in combination with high-speed oscilloscopes are the best alternative for measurement of optical waveforms with spectral coverage from 170 to 2600 nm (VUV to IR). For example, photodetectors with rise time 10 ps and bandwidth 30 GHz in combination with 50 GHz sampling oscilloscope can be successfully used to measure optical pulse widths down to 10 ps using deconvolution. Configurations of the photodetectors include free-space, fiber receptacle or SM-fiber-pigtailed options and have compact metal housings for noise immunity. The UV-extended versions of the Si photodiodes are the only commercial products that cover the spectral range from 170 to 1100 nm with a rise time < 50 ps. For maximum flexibility, most models are not internally terminated. A 50 Ohm external termination supports the specified highest speed operation.
⚙ hardware
The FSAC benchtop interferometric autocorrelator manufactured by Thorlabs is designed to characterize ultrafast pulse durations from 15 — 1,000 fs in the 650 — 1100 nm range. This autocorrelator for use with femtosecond lasers complements our ultrafast family of lasers, amplifiers, and specialized optics, including nonlinear crystals, chirped mirrors, low GDD mirrors/beamsplitters, and dispersion compensating fiber.
⚙ hardware
Our compact ultrafast autocorrelator is used to characterize ultrafast laser pulses originating from Ti:sapphire and Yb:doped lasers. Featuring a built-in two-photon absorption (TPA) detector, this autocorrelator is ideal for measuring ultrafast femtosecond and picosecond laser pulses at wavelengths from 700 to 1100 nm. The highly sensitive TPA detector allows for measurements of ultrafast laser pulses with high sensitivity by eliminating the need for angle tuning of the SHG nonlinear crystal.
Bibliography
| [1] | C. Yan and J. C. M. Diels, “Amplitude and phase recording of ultrashort pulses”, J. Opt. Soc. Am. B 8 (6), 1259 (1991); doi:10.1364/JOSAB.8.001259 |
|---|---|
| [2] | D. J. Kane and R. Trebino, “Characterization of arbitrary femtosecond pulses using frequency-resolved optical gating”, IEEE J. Quantum Electron. 29 (2), 571 (1993); doi:10.1109/3.199311 |
| [3] | D. J. Kane and R. Trebino, “Single-shot measurement of the intensity and phase of an arbitrary ultrashort pulse by using frequency-resolved optical gating”, Opt. Lett. 18 (10), 823 (1993); doi:10.1364/OL.18.000823 |
| [4] | V. Wong and I. A. Walmsley, “Analysis of ultrashort pulse-shape measurement using linear interferometers”, Opt. Lett. 19 (4), 287 (1994); doi:10.1364/OL.19.000287 |
| [5] | K. C. Chu et al., “Direct measurement of the spectral phase of femtosecond pulses”, Opt. Lett. 20 (8), 904 (1995); doi:10.1364/OL.20.000904 |
| [6] | I. A. Walmsley and V. Wong, “Characterization of the electric field of ultrashort optical pulses”, J. Opt. Soc. Am. B 13 (11), 2453 (1996); doi:10.1364/JOSAB.13.002453 |
| [7] | I. D. Jung et al., “High-dynamic-range characterization of ultrashort pulses”, Appl. Phys. B 65, 307 (1997); doi:10.1007/s003400050277 |
| [8] | R. Trebino et al., “Measuring ultrashort laser pulses in the time–frequency domain using frequency-resolved optical gating”, Rev. Sci. Instrum. 68, 3277 (1997); doi:10.1063/1.1148286 |
| [9] | C. Iaconis and I. A. Walmsley, “Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses”, Opt. Lett. 23 (10), 792 (1998); doi:10.1364/OL.23.000792 |
| [10] | L. Gallmann et al., “Characterization of sub-6-fs optical pulses with spectral phase interferometry for direct electric-field reconstruction”, Opt. Lett. 24 (18), 1314 (1999); doi:10.1364/OL.24.001314 |
| [11] | L. Gallmann et al., “Techniques for the characterization of sub-10-fs optical pulses: a comparison”, Appl. Phys. B 70, S67 (2000); doi:10.1007/s003400000307 |
| [12] | L. Gallmann et al., “Spatially resolved amplitude and phase characterization of femtosecond optical pulses”, Opt. Lett. 26 (2), 96 (2001); doi:10.1364/OL.26.000096 |
| [13] | J. W. Nicholson and W. Rudolph, “Noise sensitivity and accuracy of femtosecond pulse retrieval by phase and intensity from correlation and spectrum only (PICASO)”, J. Opt. Soc. Am. B 19 (2), 330 (2002); doi:10.1364/JOSAB.19.000330 |
| [14] | T. Hirayama and M. Sheik-Bahae, “Real-time chirp diagnostic for ultrashort laser pulses”, Opt. Lett. 27 (10), 860 (2002); doi:10.1364/OL.27.000860 |
| [15] | E. M. Kosik et al., “Interferometric technique for measuring broadband ultrashort pulses at the sampling limit”, Opt. Lett. 30 (3), 326 (2005); doi:10.1364/OL.30.000326 |
| [16] | S. Akturk et al., “The general theory of first-order spatio-temporal distortions of Gaussian pulses and beams”, Opt. Express 13 (21), 8642 (2005); doi:10.1364/OPEX.13.008642 |
| [17] | R. Paschotta et al., “Relative timing jitter measurements with an indirect phase comparison method”, Appl. Phys. B 80 (2), 185 (2005); doi:10.1007/s00340-004-1704-2 |
| [18] | A. S. Wyatt et al., “Sub-10 fs pulse characterization using spatially encoded arrangement for spectral phase interferometry for direct electric field reconstruction”, Opt. Lett. 31 (12), 1914 (2006); doi:10.1364/OL.31.001914 |
| [19] | C. Dorrer, “High-speed measurements for optical telecommunication systems”, J. Sel. Top. Quantum Electron. 12 (4), 843 (2006); doi:10.1109/JSTQE.2006.876304 |
| [20] | P. K. Bates et al., “Ultrashort pulse characterization in the mid-infrared”, Opt. Lett. 35 (9), 1377 (2010); doi:10.1364/OL.35.001377 |
| [21] | M. Chini et al., “Characterizing ultrabroadband attosecond lasers”, Opt. Express 18 (12), 13006 (2010); doi:10.1364/OE.18.013006 |
| [22] | M. Miranda et al., “Simultaneous compression and characterization of ultrashort laser pulses using chirped mirrors and glass wedges”, Opt. Express 20 (1), 688 (2012); doi:10.1364/OE.20.000688 |
| [23] | M. Rhodes et al., “Pulse-shape instabilities and their measurement”, Laser Photon. Rev. 7, 557 (2013); doi:10.1002/lpor.201200102 |
| [24] | M. Rhodes et al., “Standards for ultrashort-laser-pulse-measurement techniques and their consideration for self-reference spectral interferometry”, Appl. Opt. 53, D1 (2014); doi:10.1364/AO.53.0000D1 |
| [25] | G. Pariente et al., “Space–time characterization of ultra-intense femtosecond laser beams”, Nature Photonics 10, 547 (2016); doi:10.1038/nphoton.2016.140 |
| [26] | M. Miranda et al., “Fast iterative retrieval algorithm for ultrashort pulse characterization using dispersion scans”, J. Opt. Soc. Am. B 34 (1), 190 (2017); doi:10.1364/JOSAB.34.000190 |
| [27] | M. Miranda et al., “All-optical measurement of the complete waveform of octave-spanning ultrashort light pulses”, Opt. Lett. 44 (2), 191 (2019); doi:10.1364/OL.44.000191 |
| [28] | W. Cho et al., “Temporal characterization of femtosecond laser pulses using tunneling ionization in the UV, visible, and mid-IR ranges”, Scientific Reports 9, 16067 (2019); doi:10.1038/s41598-019-52237-y |
| [29] | I. Sytcevich et al., “Characterizing ultrashort laser pulses with second harmonic dispersion scans”, J. Opt. Soc. Am. B 38 (5), 1546 (2021); doi:10.1364/JOSAB.412535 |
(Suggest additional literature!)
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