Direct and quantitative broadband absorptance micro/nano spectroscopy using FTIR and bilayer cantilever probes

Abstract

Optical properties of micro/nano materials are important for many applications in biology, optoelectronics, and energy. In this thesis, a method is described to directly measure the quantitative absorptance spectra of micro/nano-sized structures using Fourier Transform Spectroscopy (FTS). The measurement technique combines optomechanical cantilever probes with a modulated broadband light source from an interferometer for spectroscopic measurements of objects. Previous studies have demonstrated the use of bilayer (or multi-layer) cantilevers as highly sensitive heat flux probes with the capability of resolving power as small as ~4 pW. Fourier Transform Spectroscopy is a well-established method to measure broadband spectra with significant advantages over conventional dispersive spectrometers such as a higher power throughput and large signal-to-noise ratio for a given measurement time. By integrating a bilayer cantilever probe with a Michelson interferometer, the new platform is capable of measuring broadband absorptance spectra from 3prm to 18pm directly and quantitatively with an enhanced sensitivity that enables the characterization of micro- and nanometer-sized samples, which cannot be achieved by using conventional spectroscopic techniques. Besides, a paralleled project of a bi-armed cantilever decouples the sample arm and the probe arm to further enhance the signal-to-noise ratio.