An algorithm for characterizing attosecond extreme ultraviolet pulses that is not bandwidth-limited, requires no interpolation of the experimental data, and makes no approximations beyond the ...strong-field approximation is introduced. This approach fully incorporates the dipole transition matrix element into the retrieval process. Unlike attosecond retrieval methods such as phase retrieval by omega oscillation filtering (PROOF), or improved PROOF, it simultaneously retrieves both the attosecond and infrared (IR) pulses, without placing fundamental restrictions on the IR pulse duration, intensity or bandwidth. The new algorithm is validated both numerically and experimentally, and is also found to have practical advantages. These include an increased robustness to noise, and relaxed requirements for the size of the experimental dataset and the intensity of the streaking pulse.
Pulse characterization in ultra-fast optics presents a powerful motivation to study phase retrieval problems of high order. Frequency- and time-resolved techniques for pulse characterization both ...construct measurements that depend on the intensity of the cross-correlation between two unknown signals undergoing known modulations. The problem of recovering these signals has been traditionally studied and solved with alternating minimization, but recently Wirtinger gradient techniques were demonstrated to invert frequency-resolved measurements on a symmetric signal pair (Pinilla et al., 2019). In this paper, we construct a generalized Wirtinger gradient and Hessian to solve a wide breadth of problems including signal recovery from time- and frequency-resolved measurements. We further demonstrate that both measurement paradigms are special cases of low-rank phase retrieval but with a special structure that disrupts spectral initializers. To combat this problem, we present a tensor-based iterative hard thresholding initializer that, when paired with a Wirtinger gradient descent, is capable of recovering unknown signals with fewer measurements than matrix-based alternating minimization or spectral initialization methods. Finally, we employ Wirtinger gradient descent to recover signals from real-world DSCAN (Wilhelm et al., 2021) measurements and compare results with the existing state-of-the-art.
•Optical pulse characterization is motivation for high order phase retrieval.•Wirtinger gradient techniques are effective for bivariate pulse recovery problems.•Spectral initializers fall short as an effective initializer for pulse characterization.•Iterative hard tensor thresholding is a costly but effective initializer.•Wirtinger gradient descent is used to recover signals from DSCAN measurements.
On the Uniqueness of FROG Methods Bendory, Tamir; Sidorenko, Pavel; Eldar, Yonina C.
IEEE signal processing letters
24, Issue:
5
Journal Article
Peer reviewed
Open access
The problem of recovering a signal from its power spectrum, called phase retrieval, arises in many scientific fields. One of many examples is ultrashort laser pulse characterization, in which the ...electromagnetic field is oscillating with ~1015 Hz and phase information cannot be measured directly due to limitations of the electronic sensors. Phase retrieval is ill-posed in most of the cases, as there are many different signals with the same Fourier transform magnitude. To overcome this fundamental ill-posedness, several measurement techniques are used in practice. One of the most popular methods for complete characterization of ultrashort laser pulses is the frequency-resolved optical gating (FROG). In FROG, the acquired data are the power spectrum of the product of the unknown pulse with its delayed replica. Therefore, the measured signal is a quartic function of the unknown pulse. A generalized version of FROG, where the delayed replica is replaced by a second unknown pulse, is called blind FROG. In this case, the measured signal is quadratic with respect to both pulses. In this letter, we introduce and formulate FROG-type techniques. We then show that almost all band-limited signals are determined uniquely, up to trivial ambiguities, by blind FROG measurements (and thus also by FROG), if in addition we have access to the signals power spectrum.
Plasmonic nanoantennas are efficient devices to concentrate light in spatial regions much smaller than the wavelength. Only recently, their ability to manipulate photons also on a femtosecond time ...scale has been harnessed. Nevertheless, designing the dynamical properties of optical antennas has been difficult since the relevant microscopic processes governing their ultrafast response have remained unclear. Here, we exploit frequency-resolved optical gating to directly investigate plasmon response times of different antenna geometries resonant in the near-infrared. Third-harmonic imaging is used in parallel to spatially monitor the plasmonic mode patterns. We find that the few-femtosecond dynamics of these nanodevices is dominated by radiative damping. A high efficiency for nonlinear frequency conversion is directly linked to long plasmon damping times. This single parameter explains the counterintuitive result that rod-type nanoantennas with minimum volume generate by far the strongest third-harmonic emission as compared to the more bulky geometries of bow-tie-, elliptical-, or disk-shaped specimens.
The control and data acquisition of homemade, second harmonic generation (SHG) multi‐shot frequency‐resolved optical gating (FROG) diagnostic technique reported here. We have designed and developed ...the computer controlled multi‐shot FROG diagnostic system using reflecting optics to minimize the dispersion while LabVIEW software has employed to control and data acquisition. The femtosecond laser system at laboratory for intense lasers (L2I) optimized and characterized using LabVIEW‐based FROG system. We have measured and retrieved the oscillator and compressed amplified laser pulse profiles in temporal domains having full width half maximum (FWHM) of 150 and 270 fs, respectively, and relatively small temporal phase ∼1 radians peak to peak variations with FROG error ∼0.003. The grating detuning data acquired in the form of the single data file to observe the FROG trace pattern evaluation with the change of grating positions to confirm the reliability of the LabVIEW‐based FROG system.
•Two classical methods of measuring laser pulse width are combined in one device.•All reflective configuration is used to characterize few-cycle pulses.•We consider different wavelengths effect on ...the measurement results.
Full characterization of few-cycle laser pulses is necessary in many applications. FROG is one of the most widely used full characterization techniques so far, and SRSI is another fresh one with attractive capacity. In this study, we develop a simple device FASI (frequency-resolved optical gating and self-referenced spectral interferometry), which combines the FROG and SRSI in a single device, and both of them are based on the third-order nonlinear effect of transient grating. It is compact with a size of 340 × 240 × 80 mm3. The device owns the advantages of the TG-SRSI method, which can characterize few-cycle pulses with broad spectral range from UV to mid-IR in single-shot mode for well compressed pulses. What’s more, for complex or large chirped pulses, it can also complete the characterization task by using the multi-shot TG-FROG mode. Two few-cycle pulses centered at 800 nm and 1800 nm have been characterized by using this device to verify its ability. It turned out that the proposed FASI device is a powerful tool for broad spectral range few-cycle laser pulses characterization.
We report on the 825‐nm center wavelength, 9.17 mJ pulse energy Ti:sapphire‐based femtosecond laser system simulation carried out by Lab2 tools in LabVIEW (National Instruments, Inc.). The design ...investigation and characterization of stretched, amplified and compressed pulses made by intensity module and second harmonic generation frequency‐resolved optical gating module in Lab2. The minimum pulse duration of ∼37.80 fs at the output of the compressor end obtained by simulations. The variation of pulse energy, FWHM and central wavelength versus number of passes in the amplifier are computed. The Lab2 tools help to design and characterize laser system before to set up on the optical table. The simulation results save time to calculate parameters which are essential in femtosecond laser system designing. The Lab2 simulation tools, along with financial constraints, it is easier, simple, and efficient to obtain results in short time.
•Generation of few-cycle phase-stabilized mid-infrared pulses.•Nonlinear spectral broadening in gallium gadolinium garnet.•f-3f interferometry.•Interferometric third-harmonic frequency-resolved ...optical gating.
We report on generation and characterization of few-cycle laser pulses with the central wavelength of 2 μm at repetition rate of 50 kHz. The source is based on noncollinear parametric amplification and difference frequency generation leading to passively stabilized carrier-envelope phase (CEP). CEP is characterized using f-3f technique based on spectral interference between the fundamental spectrum broadened via self-phase modulation and the third harmonics, which are both generated by tight focusing of the pulses to gallium gadolinium garnet (GGG) crystal. We demonstrate the capability of this technique for CEP measurement and long-term stabilization. Further we show that the pulses can be compressed to a duration of 1.7 optical cycles after spectral broadening in the GGG crystal.
Frequency-resolved optical gating (FROG) is a novel means of measuring the fast motion of a critical density surface during relativistic laser–plasma interaction. Herein, we present a design and ...demonstration results for a new single-shot FROG system and optical transport system for characterizing the instantaneous intensity and phase at the LFEX (Laser for Fast Ignition Experiment) laser facility at the Institute of Laser Engineering of Osaka University. At LFEX, the laser intensity at the vacuum window is intrinsically high because of two unique properties, namely, the large F-number of the off-axis parabolic mirror and the small radius of the interaction chamber. Consequently, to obtain an accurate FROG trace, attention must be paid to spectrum modulation due to self-phase modulation. The appropriate laser intensity for FROG operation was investigated experimentally, and an optical transport system with an energy attenuator composed of reflective optics was designed to eliminate the concern of spectrum modulation from measurements. A FROG trace recorded at LFEX shot with 161 J energy was reconstructed 100 times using an iterative phase-retrieval algorithm. Despite some differences in structure, the reconstructed spectrum agrees reasonably well with the spectrum obtained by a time-integrated spectrometer. This shows that the developed FROG system and the optical transport system can measure the instantaneous intensity and phase of a laser pulse without spectrum modulation.
We introduce a practical self-referenced device for the complete temporal intensity-and-phase measurement of few-femtojoule-level fs and ps pulses based on the simple version of ...frequency-resolved-optical gating, called GRENOUILLE. We replace the usual crossed-beam line-focus geometry with a point-focus near-collinear-beam geometry and a traditional delay line that allows a longer path length in the nonlinear medium, yielding greater sensitivity. As an initial demonstration of the device, we measured moderately complex pulses at energies as weak as 24 fJ with high signal-to-noise ratio. We confirmed the results measured using our technique to that of a standard GRENOUILLE and a high-resolution spectrometer.
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