Ultrabroadband Moth-Eye Antireflection Structures on GaSe Produced by Focused-Ion Beam Milling

Minimizing losses and suppression of reflection-induced echos in thin nonlinear crystals is of critical importance to both classical time-domain spectroscopy and time-domain quantum electrodynamics [1] . GaSe represents an important material in this context. However, it is challenging to coat and manipulate using macroscopic methods due to its van-der-Waals-bonded structure of hexagonal monolayers and atomically flat surfaces. At least, some progress relying on femtosecond laser ablation was demonstrated recently [2] .