Measurement and control of spatiotemporal couplings via white-light interferometry

Abstract

Ultrashort broadband pulses can exhibit spatio-temporal couplings (STCs), where the spatial and temporal properties of the beam are introduced by dispersive optical elements. These couplings, including spatial chirp, pulse-front tilt, and pulse-front curvature, can degrade pulse focusing and affect experiments using broadband ultrashort pulses.

This project investigates STCs introduced by optical elements using a supercontinuum source and a spatially resolved Fourier-transform interferometer. A spatially filtered supercontinuum beam was first characterized as a reference, and a pair of convex lenses arranged as a 1:1 telescope was then used to introduce controlled pulse-front curvature. The measured interferograms were reconstructed to obtain spatially resolved wavefront and pulse-front information. In addition, ray-tracing simulations of a 4f pulse-shaping system were performed in FRED to explore possible STC control.

The results show that the reference beam has a relatively uniform spatio-spectral distribution with negligible spatial chirp and weak angular dispersion over the 600--1000 nm spectral range. After insertion of the telescope, measurable spatial-frequency coupling and clear pulse-front curvature were observed. The study demonstrates that spatially resolved Fourier-transform interferometry can be used to identify STCs introduced by optical components, while the 4f simulations provide a basis for future controlled STC manipulation.

Popular Abstract

Light is something we encounter every moment of our lives, yet most of the light around us — sunlight, lamplight — is steady and continuous. Laser light can be different. With the right techniques, a laser can pack its energy into incredibly brief bursts, pulses lasting only a few femtoseconds. To grasp how short that is: a femtosecond is to one second what one second is to about thirty million years. These flashes are so brief that they can freeze the fastest motions in nature — electrons motion inside atoms, chemical bonds forming and breaking. But there is a subtle catch hidden inside this brevity. Because a pulse is so short in time, it cannot be a single pure color; it must be built from a whole range of colors at once, packed tightly into one tiny flash. The shorter the pulse, the broader its rainbow. This rainbow is the source of the pulse’s power — and also where trouble can quietly begin.

The trouble appears whenever such a pulse passes through ordinary optical elements — a lens, a prism, a grating, and even a slightly tilted mirror. Each color in the rainbow can bend a little differently or arrive at a slightly different moment. When this happens, the pulse’s behavior in space and time becomes tangled together and can no longer be described separately. We call this a spatio-temporal coupling, or STC. In an ideal pulse, every point across the beam experiences the same flash at the same instant; but once an STC is present, the pulse can arrive tilted across the beam or curved like a smile, so that its very shape depends on where you look. Sometimes these couplings are unwanted, blurring a pulse just when we want it to be at its sharpest; other times, they are crafted on purpose to create entirely new forms of light. Either way, seeing and understanding them is a key part of mastering the world of ultrafast optics.

• author: Wu, Houda
• supervisor: Cord Arnold; Chen Guo
• organization: Atomic Physics; Department of Physics
• course: PHYM03 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• publication/series: Lund reports on atomic physics (LRAP)
• report number: LRAP625
• language: English
• id: 9242669
• date added to LUP: 2026-08-31 09:32:01
• date last changed: 2026-08-31 09:32:01