Mid-infrared wide-field nanoscopy

• Published in: Nature photonics 2024-07, Vol.18 (7), p.738-743
• Main Authors: Tamamitsu, Miu, Toda, Keiichiro, Fukushima, Masato, Badarla, Venkata Ramaiah, Shimada, Hiroyuki, Ota, Sadao, Konishi, Kuniaki, Ideguchi, Takuro
• Format: Article
• Language: English
• Subjects: 631/1647/328/2238; 639/624/1075/1082; 639/624/1107/328/2238; Analytical chemistry; Aperture; Aperture imaging; Applied and Technical Physics; Chemical analysis; Infrared analysis; Infrared imaging; Infrared spectroscopy; Light; Light diffraction; Light sources; Nondestructive testing; Numerical aperture; Optics; Photodegradation; Photonics; Physics; Physics and Astronomy; Point spread functions; Quantum Physics; Resolution; Spatial discrimination; Spatial resolution; Spectrum analysis; Thermal imaging; Ultraviolet radiation; Wavelength
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-024-01423-0

Mid-infrared (MIR) spectroscopy is widely recognized as a powerful, non-destructive method for chemical analysis. However, its utility is constrained by a micrometre-scale spatial resolution imposed by the long-wavelength MIR diffraction limit. This limitation has been recently overcome by MIR photothermal imaging, which detects photothermal effects induced in the vicinity of MIR absorbers using a visible-light microscope. Despite its promise, the full potential of its spatial resolving power has not been realized. Here we present an optimal implementation of wide-field MIR photothermal imaging to achieve high spatial resolution. This was accomplished by employing single-objective synthetic-aperture quantitative phase imaging with synchronized subnanosecond MIR and visible light sources, effectively suppressing the resolution-degradation effect caused by photothermal heat diffusion. We demonstrated far-field MIR spectroscopic imaging with a spatial resolution limited by the visible diffraction, down to 120 or 175 nm in terms of the Nyquist–Shannon sampling theorem or full-width at half-maximum of the point spread function, respectively, in the MIR region of 3.12–3.85 μm (2,600–3,200 cm −1 ). This technique—through the use of a shorter visible wavelength and/or a higher objective numerical aperture—holds the potential to achieve a spatial resolution of less than 100 nm, thus paving the way for MIR wide-field nanoscopy. Wide-field mid-infrared photothermal imaging is developed to supress the resolution degradation caused by photo-thermal heat diffusion. By employing a single-objective synthetic-aperture imaging with synchronized subnanosecond mid-infrared and visible light sources, spatial resolution of 120 nm is obtained.