Previous work in physics

"Coherent Control of the Route of an Ultrafast Magnetic Phase Transition via Low-Amplitude Spin Precession"

(with I. Razdolski, A. M. Kalashnikova, R. V. Pisarev, A. M. Balbashov, A. Kirilyuk, Th. Rasing, and A. V. Kimel)

Phys. Rev. Lett. 108, 157601 (2012)

Editors' Suggestion and featured in Physics

Time-resolved magneto-optical imaging of laser-excited rare-earth orthoferrite (SmPr)FeO₃ demonstrates that a single 60 fs circularly polarized laser pulse is capable of creating a magnetic domain on a picosecond time scale with a magnetization direction determined by the helicity of light. Depending on the light intensity and sample temperature, pulses of the same helicity can create domains with opposite magnetizations. We argue that this phenomenon relies on a twofold effect of light which (i) instantaneously excites coherent low-amplitude spin precession and (ii) triggers a spin reorientation phase transition. The former dynamically breaks the equivalence between two otherwise degenerate states with opposite magnetizations in the high-temperature phase and thus controls the route of the phase transition.

"Laser-induced ultrafast spin dynamics in ErFeO₃"

(with I. Razdolski, A.V. Kimel, R. V. Pisarev, A. Kirilyuk, and Th. Rasing)

Phys. Rev. B 84, 104421 (2011)

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ErFeO₃. The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point T_comp ≈ 47 K and the spin reorientation transition region in the interval 86 K ≲ T ≲ 99 K. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ErFeO₃ is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the Er³⁺ 4f electrons with the lattice.

"High-dimensional mode analyzers for spatial quantum entanglement"

(with S. S. R. Oemrawsingh, X. Ma, A. Aiello, E. R. Eliel, G. W. ’t Hooft, and J. P. Woerdman)

Phys. Rev. A 73, 032339 (2006)

By analyzing entangled photon states in terms of high-dimensional spatial mode superpositions, it becomes feasible to expose high-dimensional entanglement, and even the nonlocality of twin photons. To this end, a proper analyzer should be designed that is capable of handling a large number of spatial modes, while still being convenient to use in an experiment. We compare two variants of a high-dimensional spatial mode analyzer on the basis of classical and quantum considerations. These analyzers have been tested in classical optical experiments.

"Transverse mode coupling in an optical resonator"

(with Thijs Klaassen, Martin van Exter, and J. P. Woerdman)

Opt. lett. 30, 1959 (2005)

Small-angle scattering due to mirror surface roughness is shown to couple the optical modes and deform the transmission spectra in a frequency-degenerate optical cavity. A simple model based on a random scattering matrix clearly visualizes the mixing and avoided crossings between multiple transverse modes. These effects are visible only in the frequency-domain spectra; cavity ringdown experiments are unaffected by changes in the spatial coherence, as they probe just the intracavity photon lifetime.