Madis Lõhmus

Measuring the spatiotemporal field of ultrashort Bessel-X pulses

Using SEA TADPOLE with μm-range spatial and fs-range temporal resolution, we report the first direct spatiotemporal measurements of ultrashort Bessel-X pulses. We demonstrate their propagation invariance and superluminal velocity and verify our results with simulations.

Direct spatiotemporal measurements of accelerating ultrashort Bessel-type light bullets

We measure the spatiotemporal field of ultrashort pulses with complex spatiotemporal profiles using the linear-optical, interferometric pulse-measurement technique SEA TADPOLE. Accelerating and decelerating ultrashort, localized, nonspreading Bessel-X wavepackets were generated from a approximately 27 fs duration Ti:Sapphire oscillator pulse using a combination of an axicon and a convex or concave lens. The wavefields are measured with approximately 5 microm spatial and approximately 15 fs temporal resolutions. Our experimental results are in good agreement with theoretical calculations and numerical simulations.

Temporal focusing of ultrashort pulsed Bessel beams into Airy–Bessel light bullets

We present measurements of the impulse response of a circular phase diffraction grating in dependence of the field point location behind it. These measurements were carried out using a white-light spectral interferometry set-up, which employs photonic crystal fibers in both the signal and reference arms, and achieves a few micron spatial and almost one-wave-cycle temporal resolution. Our study shows that the grating as a simple and robust single-element optical device (i) suppresses the material-induced spread of ultrashort pulses, (ii) thereby generates the Airy–Bessel light bullets, and (iii) enables temporal focusing of the pulses at the prescribed propagation depth.

Diffraction of ultrashort optical pulses from circularly symmetric binary phase gratings

The complete spatiotemporal characterization of the diffracted field of ultrashort pulses after passing through circularly symmetric binary phase diffraction gratings is carried out. The complex field is registered at different planes behind the gratings with an ultrashort-pulse measurement technique called SEA TADPOLE. Numerical simulations based on scalar diffraction theory are compared with the measurements.

Basic diffraction phenomena in time domain

Using a recently developed technique (SEA TADPOLE) for easily measuring the complete spatiotemporal electric field of light pulses with micrometer spatial and femtosecond temporal resolution, we directly demonstrate the formation of theo-called boundary diffraction wave and Aragos spot after an aperture, as well as the superluminal propagation of the spot. Our spatiotemporally resolved measurements beautifully confirm the time-domain treatment of diffraction. Also they prove very useful for modern physical optics, especially in micro- and meso-optics, and also significantly aid in the understanding of diffraction phenomena in general.

Diffraction of ultrashort Gaussian pulses within the framework of boundary diffraction wave theory

We study the diffraction of Gaussian pulses and beams within the framework of boundary diffraction wave theory. For the first time the boundary diffraction wave theory is applied to pulsed Gaussian beams, and it is shown that the diffracted field of a pulsed Gaussian beam on a circularly symmetric aperture can be evaluated by a single 1D integration along the diffracting aperture at every point of interest. We compare theoretical simulations to experimental measurements of ultrashort pulses diffracted off a circular aperture, an opaque disc, an annular aperture, and a system of four concentric annular apertures. Using the recently developed SEA TADPOLE measurement technique, we obtain micron spatial and femtosecond temporal resolutions in the spatio-temporal measurements of the diffracted fields.

Measurement of the Spatiotemporal Electric Field of Ultrashort Superluminal Bessel-X Pulses

The space-time duality of electromagnetic waves allows for the creation of temporal waveforms and the measurement of their properties.

Directly recording diffraction phenomena in time domain

By making use of a new technique for measuring the complete spatiotemporal electric field of light with micrometer spatial and femtosecond temporal resolution, we directly demonstrate the formation of the so-called boundary diffraction wave and Arago’s spot, as well as the superluminal propagation of a “diffraction-free” pulse. We believe that such spatiotemporally resolved measurements and the time-domain treatment of diffracting waves not only turn out to be useful for modern physical optics, especially in micro- and meso-optics, but also significantly aid in the understanding of diffraction phenomena in general.

Propagation of ultrashort pulses behind diffracting screens

We study the diffraction of Gaussian pulses and beams within the framework of boundary diffraction wave theory. For the first time the boundary diffraction wave theory is applied to pulsed Gaussian beams, and it is shown that the diffracted field of a pulsed Gaussian beam on a circularly symmetric aperture can be evaluated by a single 1D integration along the diffractive aperture of every point of interest. We compare the theoretical simulations to experimental measurements of ultrashort pulses diffracted off a circular aperture, an opaque disc, an annular aperture, and a system of four concentric annular apertures. Using the recently developed SEA TADPOLE measurement technique, we obtain micron spatial and femtosecond temporal resolutions in the spatio-temporal measurements of the diffracted fields.

Measuring the spatiotemporal electric field of superluminal ultrashort pulses

Using a high spatial and temporal-resolution pulse measurement technique (SEA TADPOLE), we make direct measurements of the spatiotemporal field of ultrashort Bessel-X pulses. Their propagation invariance and superluminal velocity are measured and verified with simulations.