Conference Agenda

In this talk, I will review the recent advances of the AOP team and collaborators in employing nonlinear metasurfaces to replace conventional infrared (IR) imaging techniques. I will talk through our strategies to address several challenges, including low nonlinear efficiency, limited reconfigurability, and unwanted absorption at higher frequencies. I will showcase our broadband nonlinear imaging via silicon disk-on-slab metasurfaces. This enabled direct conversion of a broad IR image, spanning>1000 to 4000 nm, into visible light. Subsequently, I will discuss real-time programmable nonlinear imaging by combining evolutionary algorithms with spatial light modulators to control wavefronts dynamically via a single metasurface. Finally, I will demonstrate our strategy for using SLM to construct a virtual metalens that enables precise control of the generated nonlinear optical field.

We investigate harmonic generation in silicon-based metasurfaces operating in the visible and UV spectrum. Our combined experimental-theoretical study reveals orders-of-magnitude enhancement of the second, third, and higher order harmonic generation. Resonant field confinement in the metasurfaces enable an enhaced efficient deep-UV emission and predictive design of nonlinear nanophotonic devices in frequency range where Si-based materials are usually not considered because they present strong absorption.

High-harmonic generation (HHG) has enabled attosecond light

pulses and table-top sources of the extreme ultraviolet light and soft X-rays.

Although HHG has long been associated with gases and plasmas,

metasurfaces are emerging as a compact, all-solid-state alternative for both

the generation and control of high harmonics. Here we demonstrate up to

11th harmonic generation from metasurfaces and up to 7th harmonic

generation from individual subwavelength resonators. We show

enhancement of HHG with Mie resonances and with modes associated with

bound states in the continuum. We explore chiral effects in HHG driven by

the symmetries of nanostructured solids. We achieve asymmetry in HHG

with respect to reversals of the direction of excitation via magneto-electric

coupling in subwavelength resonators. These results expand capabilities of

non-linear metasurfaces for simultaneous enhancement and control of high

harmonics emission, advancing functional strong field nanophotonics.

Nonlinear metasurfaces enable precise local phase control of harmonic signals, but their response is generally fixed during fabrication. This work introduces mechanical rotation as a dynamic tool to tune the phase-matching conditions of second-harmonic generation (SHG).

The approach utilizes a dual-metasurface multipass cell with each metasurface containing C3v-symmetric, three-bladed gold nanoparticles. By rotating one metasurface by an angle relative to the other, a nonlinear Pancharatnam-Berry (PB) phase is imparted to the SHG signal. Due to the threefold symmetry of the meta-atoms, a full 2-pi phase-tuning cycle is achieved with only 120 degrees of physical rotation, while the pump remains unaffected.

Experimentally, we observed a continuous and controlled spectral shift of the SHG phase-matching peaks across a pump wavelength range of 900 to 970 nm. The results show excellent agreement with theoretical predictions, confirming that this geometric phase control is robust and decoupled from conversion efficiency. This work establishes mechanical rotation as a practical mechanism for reconfigurable nonlinear flat optics, with applications in tunable frequency conversion and compact pulse characterization.

Characterization of the quality factor (Q) is an important part of the

studies of resonant optical system. The value of Q is typically determined from

spectral linewidth measurements. However, this approach is limited by the fi

nite resolution of spectrometers and ambiguity arising from asymmetric Fano

like lineshapes. Here, we experimentally demonstrate a time-resolved nonlin

ear pump–probe method based on sum-frequency generation (SFG) to deter

mine the Q factor directly from the temporal decay of the resonant excitation.

By operating in the time domain, this approach circumvents the spectral reso

lution constraints and reduces the uncertainty associated with spectral fitting.

As an example, we use this method to demonstrate a Q factor of 1300 for a

quasi-bound state in the continuum (quasi-BIC) in a gallium indium phosphide

(GaInP) metasurface. These results establish a complementary and robust ap

proach to characterize the Q factor of high-Q resonant photonic systems.