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Complete characterization of ultrashort optical pulses with a phase-shifting wedged reversal shearing interferometer.

ABSTRACT: The ability of an interferometer to characterize the spatial information of a light beam is often limited by the temporal profile of the beam, with femtosecond pulse characterization being particularly challenging. In this study, we developed a simple, stable, controllable shearing and vectorial phase-shifting wedged reversal shearing interferometer that is able to characterize all types of coherent and partially coherent light beams. The proposed interferometer consists of only a single beam splitter cube with one wedged entrance face and is insensitive to environmental vibration due to its common path configuration. A near zero-path length difference of the proposed interferometer ensures its operation for ultrashort pulses, providing, for the first time, a simple and stable interferometric tool to fully characterize sub-100 fs laser pulses. All common beam characterization can be carried out with the interferometer, such as the amplitude, phase, polarization, wavelength, and pulse duration. Furthermore, this technique is sensitive to the wavefront tilt and can be used for precise beam alignment. Therefore, this interferometer can be an essential tool for beam characterization, optical imaging, and the testing required for a wide range of applications, including astronomy, biomedicine, ophthalmology, optical testing and imaging systems, and adaptive optics.

SUBMITTER: Lam B

PROVIDER: S-EPMC6106999 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Radiofrequency phase encoded half-pulses in simultaneous multislice ultrashort echo time imaging.

Project description:PurposeTo describe a simultaneous multislice (SMS) ultrashort echo time (UTE) imaging method using radiofrequency phase encoded half-pulses in combination with power independent of number of slices (PINS) inversion recovery (IR) pulses to generate multiple-slice images with short T2 * contrasts in less than 3 min with close to an eightfold acceleration compared with a standard 2D approach.Theory and methodsRadiofrequency phase encoding is applied in an SMS (NSMS = 4) excitation scheme using "sinc" half-pulses. With the use of coil sensitivity encoding (SENSE) and controlled aliasing in parallel imaging (CAIPI) in combination with a gradient echo 2D spiral readout trajectory and IR PINS pulses for contrast enhancement a fast UTE sequence is developed. Images are obtained using a model-based reconstruction method. Sequence details and performance tests on phantoms as well as the heads of healthy volunteers at 3T are presented.ResultsAn SMS UTE sequence with an undersampling factor of 4 is developed using radiofrequency phase encoded half-pulses and PINS IR pulses which enables the acquisition of 8 slices at 0.862 mm2 resolution in less than 3-min scan time. UTE images of the head are obtained showing highlighted signal of cortical bone. Image quality and T2 contrast are comparable to the one obtained by corresponding single slice acquisitions with only minor deviations.ConclusionsThe method combining radiofrequency phase encoded SMS half-pulses and PINS IR pulses presents a suitable approach to SMS UTE imaging. The usage of coil sensitivity information and increased sampling density by means of interleaved slice group acquisitions allows to reduce the total scan time by a factor close to 8.

| S-EPMC6435423 | biostudies-literature

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| S-EPMC3926000 | biostudies-literature

Simultaneous Characterization of Two Ultrashort Optical Pulses at Different Frequencies Using a WS<sub>2</sub> Monolayer.

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| S-EPMC9204806 | biostudies-literature

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| S-EPMC2717245 | biostudies-literature

Ultrashort spin-orbit torque generated by femtosecond laser pulses.

Project description:To realize the very objective of spintronics, namely the development of ultra-high frequency and energy-efficient electronic devices, an ultrafast and scalable approach to switch magnetic bits is required. Magnetization switching with spin currents generated by the spin-orbit interaction at ferromagnetic/non-magnetic interfaces is one of such scalable approaches, where the ultimate switching speed is limited by the Larmor precession frequency. Understanding the magnetization precession dynamics induced by spin-orbit torques (SOTs) is therefore of great importance. Here we demonstrate generation of ultrashort SOT pulses that excite Larmor precession at an epitaxial Fe/GaAs interface by converting femtosecond laser pulses into high-amplitude current pulses in an electrically biased p-i-n photodiode. We control the polarity, amplitude, and duration of the current pulses and, most importantly, also their propagation direction with respect to the crystal orientation. The SOT origin of the excited Larmor precession was revealed by a detailed analysis of the precession phase and amplitude at different experimental conditions.

| S-EPMC9747954 | biostudies-literature

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Project description:We report on damage to DNA in an aqueous medium induced by ultrashort pulses of intense laser light of 800 nm wavelength. Focusing of such pulses, using lenses of various focal lengths, induces plasma formation within the aqueous medium. Such plasma can have a spatial extent that is far in excess of the Rayleigh range. In the case of water, the resulting ionization and dissociation gives rise to in situ generation of low-energy electrons and OH-radicals. Interactions of these with plasmid DNA produce nicks in the DNA backbone: single strand breaks (SSBs) are induced as are, at higher laser intensities, double strand breaks (DSBs). Under physiological conditions, the latter are not readily amenable to repair. Systematic quantification of SSBs and DSBs at different values of incident laser energy and under different external focusing conditions reveals that damage occurs in two distinct regimes. Numerical aperture is the experimental handle that delineates the two regimes, permitting simple optical control over the extent of DNA damage.

| S-EPMC4899723 | biostudies-other

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Project description:We demonstrate a three phase-grating moiré neutron interferometer in a highly intense neutron beam as a robust candidate for large area interferometry applications and for the characterization of materials. This novel far-field moiré technique allows for broad wavelength acceptance and relaxed requirements related to fabrication and alignment, thus circumventing the main obstacles associated with perfect crystal neutron interferometry. We observed interference fringes with an interferometer length of 4 m and examined the effects of an aluminum 6061 alloy sample on the coherence of the system. Experiments to measure the autocorrelation length of samples and the universal gravitational constant are proposed and discussed.

| S-EPMC8667086 | biostudies-literature

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Project description:Targeted chemical modification of peptides and proteins by laser pulses in a biologically relevant environment, i.e. aqueous solvent at room temperature, allows for accurate control of biological processes. However, the traditional laser methods of control of chemical reactions are applicable only to a small class of photosensitive biomolecules because of strong and ultrafast perturbations from biomolecule-solvent interactions. Here, we report excitation of harmonics of vibration modes of solvent molecules by femtosecond laser pulses to produce controlled chemical modifications of non-photosensitive peptides and proteins in polar liquids under room conditions. The principal modifications included lysine formylation and methionine sulfoxidation both of which occur with nearly 100% yield under atmospheric conditions. That modification occurred only if the laser irradiance exceeded certain threshold level. The threshold, type, and extent of the modifications were completely controlled by solvent composition, laser wavelength, and peak irradiance of ultrashort laser pulses. This approach is expected to assist in establishing rigorous control over a broad class of biological processes in cells and tissues at the molecular level.

| S-EPMC5514113 | biostudies-literature

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Project description:In this work we firstly study the influence of different parameters in the temporal characterization of ultrashort laser pulses with the recently developed amplitude swing technique. In this technique, the relative amplitude of two delayed replicas is varied while measuring their second-harmonic spectra. Here we study the retrieval of noisy traces and the implications of having different delays or phase retardations (relative phases) between the two replicas. Then, we study the capability of the technique to characterize the pulses when the second-harmonic signal is spectrally uncalibrated or incomplete, presenting the analytical calculation of the marginal, which is used to calibrate the traces and to perform the pulse retrievals. We experimentally show the retrieval of different pulses using diverse delays and phase retardations to perform the amplitude swing trace and demonstrate that, from an uncalibrated trace, both the pulse information and the response of the nonlinear process can be simultaneously retrieved. In sum, the amplitude swing technique is shown to be very robust against experimental constraints and limitations, showing a high degree of soundness.

| S-EPMC7591537 | biostudies-literature

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| S-EPMC5532372 | biostudies-literature

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