Ultra-broadband cryogenic nanoscopy: The next evolution in tabletop nano-optics

The spatial dimensions natural to many quantum materials ranging from complex oxides to twisted van der Waals multilayers lie characteristically at the nano-scale, which poses a barrier to resolving phenomena in these materials with conventional bulk probes like optical spectroscopy. Thankfully, the recent decade has witnessed rapid development of infrared nano-imaging at cryogenic temperatures, owing to seminal experiments enabled by uniquely designed scanning probe microscopes. To date however, the promise of truly broadband infrared nano-spectroscopy at liquid helium temperatures has remained unfulfilled. In fulfillment of this promise, we present a novel cryogenic Scanning Near-field Optical Microscope (cryo-SNOM) capable of ultra-stable phase-resolved nano-imaging and -spectroscopy at uninterrupted energies spanning the mid-infrared to the visible regime. Our instrument couples a unique balanced asymmetric Michelson interferometer to a high-power fiber feedback-stabilized 40 MHz optical parametric amplifier and difference frequency generation stage, supplying continuous remote energy tuning to enable nano-imaging and spectroscopy interchangeably with push-button simplicity. Moreover, we present a unique scheme integrating remote laser tuning with Fourier transform infrared spectroscopy to supply ultra-broadband spectroscopy spanning 500-2000 cm-1 and beyond. A long-range closed-loop scanner combined with helium cryostat and unique thermal insulation enable reliable operation at temperatures from 10-400K. This next evolution in cryogenic nanoscopy provides an unprecedented combination of low noise and low temperature conditions for the nano-resolved study of quantum matter across a decade of phonon energies.