Spatio-Temporal Weak Measurement of Chiral Ultra short Laser Pulse

TL;DR

The paper addresses measuring time-varying polarization in a chiral ultrafast pulse using spatio-temporal weak measurement. It implements a birefringence-induced temporal splitting read out by time-resolved leakage radiation microscopy, with a plasmonic slit providing spatial post-selection, to map the time evolution of the weak value ε(t). Key contributions include extracting both real and imaginary components of ε(t) through HWP and Faraday configurations, deriving $\\epsilon(t) = \\frac{\\ln 2 \, (t-\\tau) \, t_c}{T^2}$ and $\\tilde{\\epsilon}(\\omega) = \\ln 2 \, t_c \, (\\omega-\\omega_0)$ (with $ t_c = \\frac{2\\pi}{\\omega_0} $), and demonstrating coupled polarization dynamics (ψ(t) and χ(t)) including a Q-plate. The work advances ultrasensitive polarization metrology in nanophotonics and optical communications by enabling time-resolved weak-value measurements of ultrafast pulses.

Abstract

We present a comprehensive study on the spatio temporal weak measurement of a chiral ultrafast optical pulse. We create a chiral vector wave packet by transmitting ultrashort laser pulse via a birefringent or magneto-optic medium. Employing time-resolved leakage radiation microscopy, we examine how the real and imaginary components of the weak value parameter ($ε$) influence pulse propagation over time. Our technique allows us to detect and categorize the temporal polarization fluctuation in a $75$ fs pulse with an excellent repeatability. The achieved experimental results demonstrate a satisfactory consistency with the theoretical predictions.

Figures (11)

• Figure 1: (a) Polarization variation in space due to a tight focusing. (b),(c) Temporal polarization modulation for a pulse passing through a HWP at $0^\circ$ and at $45^\circ$. (d) Polarization state variation due to a Faraday effect.
• Figure 2: Experimental Setup and the results. (a) Schematic diagram of the experimental setup with BS - beam splitter, LP - linear polarizer, $O_1$ and $O_2$ - objectives and $L_1$ and $L_2$ lenses. (a1) Leakage radiation microscopy setup. (b) SEM image of the slit. (c) Leakage radiation (LR) image recorded at $t = 70$ fs with a perfect TE polarization. (d) Processed pulse image after filtering.
• Figure 3: Plasmonic distribution after the post-selection. (a) Measured time-snapshot of the plasmonic beams with the HWP rotated at $45^\circ$, $0^\circ$ and $-45^\circ$. (b) Polarization rotation angle variation in time calculated using Eq. \ref{['ShortEb']} for the corresponding cases of $\epsilon$.
• Figure 4: Experimental and numerical results showing the angular shift of the pulse over the time interval from $t = 32\,\text{fs}$ to $128\,\text{fs}$. The results represent measurements done with (a) HWP at $-45^\circ$, (b) HWP at $0^\circ$ and (c) HWP at $+45^\circ$. White arrows guide the eye to the angular asymmetry of the intensities.
• Figure 5: Plasmonic distribution after the post-selection of a pulse transmitted through a Faraday medium. (a) Measured time-snapshot of the plasmonic beams with a parallel, antiparallel or null magnetic field. (b) Calculated polarization ellipticity variation in time for the corresponding cases of $\epsilon$.