Measuring the Pulse Duration and the Time-Dependent Polarisation State of Ultrashort Laser Pulses with the D-Scan Technique

Abstract

Ultrashort laser pulses with time-dependent polarisation states have many applications, such as the generation of isolated attosecond pulses and the study of the optical chirality of molecules. In this project the polarisation gate, built from two quarter-wave plates of different orders, is thoroughly characterised in experiment and simulation. The time-dependent polarisation state is investigated with the dispersion scan technique (d-scan). We demonstrate that it is sufficient to measure three different projections of the electric field with the d-scan in order to achieve its complete reconstruction.

Popular Abstract

Did you know that we can produce light in pulses that last only a few femtoseconds (0.000000000000001 s)? In many applications, it is essential to have a precise characterisation of these light pulses. Since there is no event short enough to measure them, the solution lies in manipulating light for its own measurement.

The field of ultrafast science has benefited greatly from them, for the following reason: in order to observe an event, another event that can be controlled and that happens in an even shorter time is needed. This became a problem when scientists first tried to study the motion of atoms and molecules when a chemical reaction occurs, or the electron dynamics in the event of photoionisation (a photon strips an electron from an atom after collision). Fortunately, ultrashort laser pulses can be used as "flashes of light" that last a millionth of a billionth of a second, which has opened the door to the study of ultrafast processes. However, this is not their only application. When a small amount of energy is put into such a short time then the generated power (energy/time) can reach enormous values, as high as 1 PW (1000000000000000 W). This is several orders of magnitude greater than for example the power produced in a nuclear power plant. As a consequence, shining these pulses onto matter leads to different effects such as the nonlinear response of the medium, the generation of a plasma, etc. These processes can be used, for example, to cut materials with micrometer precision (0.000001 m) or to accelerate particles to almost the speed of light (300000000 m/s) in a space no larger than a table.

Linked to the generation of ultrashort laser pulses is the need for their characterisation. Just as in a camera it is important to control the exposure time, it is essential to know precisely the duration of these pulses. Another property that is important to control is the polarisation of light. Light is an electromagnetic wave and the polarisation describes the direction it oscillates. In a similar way to how the waves of the sea shape the medium through which they propagate, the oscillations of light induce the movement of electrons, atoms and molecules.

Electronic instruments cannot be used to measure the properties of ultrashort laser pulses, simply because they are not fast enough. Fortunately, there are many ways to manipulate light using optical elements such as lenses, prisms, crystals, among other things that do not require electronics. The key to measure pulses is to manipulate light itself for their own measurement, which has opened the door to a series of methods to measure their duration. In this project we have used one of these methods, called the dispersion scan (d-scan), to measure not only the duration but also the polarisation of ultrashort laser pulses.

• author: Díaz Rivas, Daniel
• supervisor: Cord Arnold; Ann-Kathrin Raab
• organization: Department of Physics; Atomic Physics
• course: PHYM03 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• keywords: pulse characterisation, ultrashort, laser, femtosecond, dispersion scan, polarisation, wave plate, temporal reconstruction, electric field reconstruction, time-dependent polarisation, polarisation gate
• publication/series: Lund reports on atomic physics (LRAP)
• report number: LRAP583
• language: English
• id: 9091170
• date added to LUP: 2022-06-21 09:15:00
• date last changed: 2022-06-21 09:15:00