Spectral Phase Interferometry Research Articles

Stannous Chloride-Modified Glass Substrates for Biomolecule Immobilization: Development of Label-Free Interferometric Sensor Chips for Highly Sensitive Detection of Aflatoxin B1 in Corn.

This study presents the development of stannous chloride (SnCl2)-modified glass substrates for biomolecule immobilization and their application in fabricating sensor chips for label-free interferometric biosensors. The glass modification process was optimized, identifying a 5% SnCl2 concentration, a 45 min reaction time, and a 150 °C drying temperature as conditions for efficient protein immobilization. Based on the SnCl2-modified glass substrates and label-free spectral-phase interferometry, a biosensor was developed for the detection of aflatoxin B1 (AFB1)-a highly toxic and carcinogenic contaminant in agricultural products. The biosensor realizes a competitive immunoassay of a remarkable detection limit as low as 26 pg/mL of AFB1, and a five-order dynamic range. The biosensor performance was validated using real corn flour samples contaminated with Aspergillus flavus. The proposed approach not only provides a powerful tool for AFB1 detection for food safety monitoring but also demonstrates the potential of SnCl2-modified substrates as a versatile platform for the development of next-generation biosensors.

SPIDERweb: a neural network approach to spectral phase interferometry

Reliably characterized pulses are the starting point of any application of ultrafast techniques. Unfortunately, experimental constraints do not always allow for optimizing the characterization conditions. This dictates the need for refined analysis methods. Here we show that neural networks can provide a viable characterization when applied to data from interferometry for direct electric-field reconstruction (SPIDER). We have adopted a cascade of convolutional networks, addressing the multiparameter structure of the interferogram with a reasonable computing power. In particular, the necessity of precalibration is reduced, thus pointing toward the introduction of neural networks in more generic arrangements.

Quantitative Rapid Magnetic Immunoassay for Sensitive Toxin Detection in Food: Non-Covalent Functionalization of Nanolabels vs. Covalent Immobilization.

In this study, we present a novel and ultrasensitive magnetic lateral flow immunoassay (LFIA) tailored for the precise detection of zearalenone, a mycotoxin with significant implications for human and animal health. A versatile and straightforward method for creating non-covalent magnetic labels is proposed and comprehensively compared with a covalent immobilization strategy. We employ the magnetic particle quantification (MPQ) technique for precise detection of the labels and characterization of their functionality, including measuring the antibody sorption density on the particle surface. Through kinetic studies using the label-free spectral phase interferometry, the rate and equilibrium constants for the binding of monoclonal antibodies with free (not bound with carrier protein) zearalenone were determined to be kon = 3.42 × 105 M-1s-1, koff = 7.05 × 10-4 s-1, and KD = 2.06 × 10-9 M. The proposed MPQ-LFIA method exhibits detection limits of 2.3 pg/mL and 7.6 pg/mL when employing magnetic labels based on covalent immobilization and non-covalent sorption, with dynamic ranges of 5.5 and 5 orders, correspondingly. We have successfully demonstrated the effective determination of zearalenone in barley flour samples contaminated with Fusarium graminearum. The ease of use and effectiveness of developed test systems further enhances their value as practical tools for addressing mycotoxin contamination challenges.

The Temporal Measurement of Infrared Femtosecond Fiber Laser Pulse with Complex Spectra: SPIDER and FROG

Femtosecond fiber laser pulse (FFLP) is very suitable for precision laser processing (PLP) with the advantages of high power, compact integrated structure, and easy installation. However, with the power increasing, nonlinear optical effects (NOE) of fiber, such as self-phase modulation (SPM), will be greatly enhanced, and the spectra of the output pulse will be very complex, which considerably increases the temporal complexity of FFLP and takes an immeasurable influence on PLP, so it is of great significance to accurately measure the temporal property of FFLP for higher accuracy of PLP. This paper presents a self-referencing spectral phase interferometry for direct electric-field reconstruction based on a single grating stretcher (SGS-SPIDER) with the two-step phase shift (TSPS) method for measuring FFLP with complex and infrared spectra. Meanwhile, we present a modified pulse-retrieval algorithm called an adaptive pulse-retrieval algorithm (APRA) of frequency-resolved optical gating (FROG) to reconstruct the measured pulse accurately. The duration of the reconstructed pulse measured by FROG is 162 fs, whose autocorrelation curve is similar to the measured autocorrelation curve including the picosecond background. The error of the reconstructed FROG trace is 0.42%, which is reliable enough according to the literature experience. Finally, the unique advantages of FROG for measuring complex ultrashort pulses such as FFLP are compared with SPIDER; that is, FROG has a wider spectral phase measuring range than SPIDER. These studies provide a new diagnostic technique for the complete temporal characterization of FFLP with complex spectra and extend the measurement range and application of SPIDER at the infrared wavelength band, which is significant for improving the accuracy of PLP using FFLP.

Fast Spectrum Measurements Using Optical Computing

Traditional spectrometers are too slow for the continuous real-time measurement of rapidly varying spectrum. Dispersive Fourier transformation (DFT) technology replaces diffraction grating and detector array in traditional spectrometers with dispersive elements and photodiodes, and therefore reaches MHz-level spectral capture rate. In addition, frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are also important ultrafast spectroscopy technologies in relevant fields. However, these approaches have to use mode-locked pulses as probe light, which may cause damages to some samples due to high peak power. Therefore, the requirement for light source restricts the scope of these technologies’ applications. Here, we report a general technique using optical computing for fast spectrum measurements, to overcome the bottleneck of light source in existing ultrafast spectroscopy measurement technologies. The proposed method has no strict requirement on the probe light. It means the common light source could also be applied for fast real-time spectroscopic measurements. In experiments, CW signals with four different optical spectra have been measured at capture speed of 1MHz respectively. The proposed method can overcome the limitations of existing ultrafast spectroscopy technologies in light source, and therefore provide a powerful tool for investigating rapid transient phenomena in many applications.

Spectral phase interferometry for direct electric-field reconstruction of synchrotron radiation

An undulator is a device widely used in synchrotron light sources to produce a certain quasi-monochromatic light; however, its waveform has never been recorded due to the lack of measurement techniques. Here we propose an approach to characterize the waveforms of electric fields produced by relativistic electrons using an algorithm of spectral phase interferometry for direct electric-field reconstruction, which is one of the most common methods to characterize ultrashort laser pulses. As a result, we have succeeded in retrieving a 10-cycle square enveloped electric field, which corresponds to 10 periods of permanent magnets of the undulator. This method can dramatically improve the development of synchrotron sources including x-ray free electron lasers.

Характеризация сверхкоротких тераваттных лазерных импульсов методом пространственно-кодированной интерферометрии спектральной фазы

Terawatt laser pulses obtained after temporal compression due to nonlinear spectrum broadening in thin glass plates with subsequent dispersion compensation by chirped mirrors are experimentally characterized by spatially encoded spectral phase interferometry. The proposed method allowed to reconstruct the spectral and temporal phase of obtained 16 fs laser pulses with up to 20 mJ of energy in a single-shot mode with spatial resolution.

Complete characterization of ultrafast optical fields by phase-preserving nonlinear autocorrelation

Nonlinear autocorrelation was one of the earliest and simplest tools for obtaining partial temporal information about an ultrashort optical pulse by gating it with itself. However, since the spectral phase is lost in a conventional autocorrelation measurement, it is insufficient for a full characterization of an ultrafast electric field, requiring additional spectral information for phase retrieval. Here, we show that introducing an intensity asymmetry into a conventional nonlinear interferometric autocorrelation preserves some spectral phase information within the autocorrelation signal, which enables the full reconstruction of the original electric field, including the direction of time, using only a spectrally integrating detector. We call this technique Phase-Enabled Nonlinear Gating with Unbalanced Intensity (PENGUIN). It can be applied to almost any existing nonlinear interferometric autocorrelator, making it capable of complete optical field characterization and thus providing an inexpensive and less complex alternative to methods relying on spectral measurements, such as frequency-resolved optical gating (FROG) or spectral phase interferometry for direct electric-field reconstruction (SPIDER). More importantly, PENGUIN allows the precise characterization of ultrafast fields in non-radiative (e.g., plasmonic) nonlinear optical interactions where spectral information is inaccessible. We demonstrate this novel technique through simulations and experimentally by measuring the electric field of ~6-fs laser pulses from a Ti:sapphire oscillator. The results are validated by comparison with the well-established FROG method.

RETRACTED ARTICLE: Sub-2-fs ultrashort optical pulses characterized by spectral phase interferometry for direct electric-field reconstruction

RETRACTED ARTICLE: Sub-2-fs ultrashort optical pulses characterized by spectral phase interferometry for direct electric-field reconstruction

Proposal for complete characterization of attosecond pulses from relativistic plasmas

In this study, we propose two full-optical-setup and single-shot measurable approaches for complete characterization of attosecond pulses from surface high harmonic generation (SHHG): SHHG-SPIDER (spectral phase interferometry for direct electric field reconstruction) and SHHG-SEA-SPIDER (spatially encoded arrangement for SPIDER). 1D- and 2D-EPOCH PIC (particle-in-cell) simulations were performed to generate the attosecond pulses from relativistic plasmas under different conditions. Pulse trains dominated by single isolated peak as well as complex pulse train structures are extensively discussed for both methods, which showed excellent accuracy in the complete reconstruction of the attosecond field with respect to the direct Fourier transformed result. Kirchhoff integral theorem has been used for the near-to-far-field transformation. This far-field propagation method allows us to relate these results to potential experimental implementations of the scheme. The impact of comprehensive experimental parameters for both apparatus, such as spectral shear, spatial shear, cross-angle, time delay, and intensity ratio between the two replicas has been investigated thoroughly. These methods are applicable to complete characterization for SHHG attosecond pulses driven by a few to hundreds of terawatts femtosecond laser systems.

Characterizing ultrashort laser pulses by the rotational Doppler effect

Technological advances in femtosecond laser sources call for the development of increasingly refined characterization tools implying to enrich the existing panel of operable nonlinear interactions. Toward that end, we have recently proposed a variant of SPIDER (spectral phase interferometry for direct electric field reconstruction) based on a nonstandard effect for producing the frequency shear, the so-called rotational Doppler effect. The method called DEER-SPIDER, for Doppler effect E-field replication, has the advantage of producing a spectral shearing at/near the fundamental wavelength, thus allowing operation in the ultraviolet spectral range. The present paper provides a deeper study of this approach. The method is tested under two different challenging conditions, and a thorough theoretical analysis is proposed. Possible improvements and an outlook are also discussed.

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass.

In this work, we report a novel method of label-free detection of small molecules based on direct observation of interferometric signal change in graphene-modified glasses. The interferometric sensor chips are fabricated via a conventional wet transfer method of CVD-grown graphene onto the glass coverslips, lowering the device cost and allowing for upscaling the sensor fabrication. For the first time, we report the use of graphene functionalized by the aptamer as the bioreceptor, in conjunction with Spectral-Phase Interferometry (SPI) for detection of ochratoxin A (OTA). In a direct assay with an OTA-specific aptamer, we demonstrated a quick and significant change of the optical signal in response to the maximum tolerable level of OTA concentration. The sensor regeneration is possible in urea solution. The developed platform enables a direct method of kinetic analysis of small molecules using a low-cost optical chip with a graphene-aptamer sensing layer.

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

Spectral-Phase Interferometry Detection of Ochratoxin A via Aptamer-Functionalized Graphene Coated Glass

Principle and technology of attosecond pulse characterization

Attosecond pulses have potential applications in the fields of physics, chemistry, biology, and medicine owing to the extremely high time resolution brought by their extremely short pulse widths. The generation and measurement technology of attosecond pulses provides a powerful means for the study of electron dynamical process in atoms. Since the date of its birth, the time width of an attosecond pulse has become shorter and shorter, making its measurement a challenging task. Although attosecond pulses are more and more widely used in the study of ultrafast dynamics and more interest is attracted into the field of attosecond science, it is undeniable that there are still difficulties and challenges for the measurement of attosecond pulses. This review is divided into two parts. The first part presents the development of technics for characterizing attosecond pulses, and briefly describes several experimental principles, setups and results for acquiring time-domain information of attosecond pulses, including RABITT (reconstruction of attosecond beating by interference of two-photon transitions) and laser-assisted lateral X-ray photoionization for measuring attosecond pulse train, attosecond streak camera for measuring single attosecond pulses, TIPTOE (tunneling ionization with a perturbation for the time-domain observation of an electric field) for measuring time-domain information of periodic pulses, as well as theoretical proposals such as attosecond cross correlation, asymmetric photoionization method, and SPIDER (attosecond spectral phase interferometry for direct electric-field reconstruction). The second part introduces the principle and structure of inversion algorithms for extracting time-domain information of attosecond pulses from spectrograms obtained with an attosecond streak camera, including FROG-CRAB (frequency resolved optical gating for complete reconstruction of attosecond bursts), PROOF (phase retrieval by omega oscillation filtering), VTGPA (Volkov transform generalized projections algorithm), PROBP-AC (phase retrieval of broadband pulses with autocorrelation) and CVGN (conditional variational generative network). We also evaluate the calculation time and accuracy of the algorithms. Finally, we summarize the experimental and theoretical challenges of the characterization of attosecond pulses, and look forward to the future development of attosecond pulse measurement.

Doppler effect as a tool for ultrashort electric field reconstruction

We present a new, to the best of our knowledge, variant of the spectral-shearing interferometry method for characterizing ultrashort laser pulses. This original approach, called Doppler effect e-field replication (DEER), exploits the rotational Doppler effect for producing frequency shear and provides spectral shearing in the absence of frequency conversion, enabling operation in the ultraviolet spectral range. Evaluation of the DEER-spectral phase interferometry for direct electric field reconstruction setup reveals a phase reconstruction of great reliability. Possible improvements, benefits, and worthwhile prospects of the method are discussed.

Second-Harmonic Young's Interference in Atom-Thin Heterocrystals.

Second-harmonic generation (SHG) is a nonlinear optical process that converts two identical photons into a new one with doubled frequency. Two-dimensional semiconductors represented by transition-metal dichalcogenides are highly efficient SHG media because of their excitonic resonances. Using spectral phase interferometry, here we directly show that SHG in heterobilayers of MoS2 and WS2 is governed by optical interference between two coherent SH fields that are phase-delayed differently in each material. We also quantified the frequency-dependent phase difference between the two, which agreed with polarization-resolved data and first-principles calculations on complex susceptibility. The second-harmonic analogue of Young's double-slit interference shown in this work demonstrates the potential of custom-designed parametric generation by atom-thick nonlinear optical materials.

Wavelet-based method for spectral interferometry filtering.

In this work, we study the effects of noise present on spectral interferometry signals, for femtosecond pulse retrieval such as in the SPIDER technique (spectral phase interferometry for direct e-field reconstruction). Although previous works report SPIDER robustness, we have found that noisy signals with low signal-to-noise ratio (SNR), in the acquired spectral interferogram, could cause variations in the temporal pulse intensity retrieval. We demonstrate that even in a filtered SPIDER signal, following standard procedures, at some point the noise on the spectral interferogram could affect the spectral phase retrieval. As a novel alternative for spectral interferograms filtering, we have applied the wavelet transform and propose a target criterion to automatize the optimization algorithm. We apply this method on SPIDER signals and analyze its effectiveness on the spectral phase retrieval. We present numerical and experimental results to show the improvement in the phase retrieval and the temporal pulse reconstruction after applying this filtering method and compare the results with a standard method.

Spatially resolved spectral phase interferometry with an isolated attosecond pulse.

We demonstrate spatially resolved supercontinuum spectral phase interferometry with an isolated attosecond pulse (IAP). The measured spatial-spectral interferogram over the broadband region indicates a high degree of IAP coherence in both spatial and spectral domains. In addition, the spectral-delay interferogram shows periodic temporal oscillations over the full IAP continuous spectrum, which indicates high temporal coherence. The supercontinuum spectral phase interferometry with broadband IAP will contribute to exploring spatiotemporal dispersive electronic dynamics through phase-based spectroscopy in the future.

CRISP: A compact RF ion source prototype for emittance scanner testing.

A movable Allison type emittance scanner is being developed to characterize the phase-space distribution of the beamlets of spectral phase interferometry for direct electric-field reconstruction, the prototype RF negative ion source of the ITER heating neutral beam injector. To test the electronics and verify the capability of the device to resolve nearby beamlets, a compact RF ion source prototype has been set up, capable of accelerating 1 mA of helium ions up to a voltage of 2 kV. A commercial 100 W RF generator creates a plasma inside a Pyrex tube, with a density between 1015 and 1016 m-3 and an electron temperature up to 15 eV. Three multi-aperture grids in accel-decel configuration extract and accelerate the ions, which are measured with a Faraday cup. We present in this paper the characterization of the ion source and its first operation, showing that it is suitable for the commissioning of the Allison scanner.