Resonantly Enhanced Infrared Up‐Conversion in Double‐Step Asymmetric Subwavelength Grating Structure (Advanced Optical Materials 32/2024)

Infrared Up-Conversion in Double-Step Asymmetric Subwavelength Grating Structure In article number 2401070, Varun Raghunathan and co-workers study the nonlinear optical up-conversion of the mid-infrared to visible wavelength range through third-order sum-frequency generation (TSFG) process using novel double-step amorphous germanium one-dimensional sub-wavelength grating structures supporting quasi-bound states in the continuum (quasi-BIC) resonances in the mid-infrared (3–3.5 mm). One-dimensional dual step gratings on the quartz substrate are shown in the bottom part of the image. The primary (with central hole) and secondary mirrors inside the reflective objective are shown as discs (glassy brown) in the middle part. Cylindrical beams represent two mixing beams: pump (orange) and mid-infrared (pink) along with the generated TSFG signal (green). Pulses with arrows represent the incoming (illumination) and outgoing (collection) beams. The central obscuration caused by the secondary mirror is also clearly illustrated, which is the main theme of the work.