Coated Spintronic Emitters for Improved THz Time-domain Spectroscopy

Spintronic metal thin films excited by femtosecond laser pulses have proven to be excellent sources of broadband THz radiation, making these emitters increasingly popular for THz spectroscopy. Unfortunately, a significant proportion of the incident excitation laser is transmitted through the spintronic emitters, which can inadvertently photoexcite samples or cause damage to elements of the spectrometer. Here, we demonstrate a high-reflectivity coating made from alternating layers of SiO
2
and Ta$_{{2}} {\mathrm{O}} _{{5}}$ that effectively blocks the incident excitation pulse and enhances the peak THz electric field by roughly 35%. We further improve the emitter performance with an anti-reflective coating. We find spintronic emitters with both coatings exhibit over 40% improvement in peak THz electric field compared to an uncoated emitter and transmit less than 0.1% of the excitation laser pulse.