Ultraviolet absorbance Mach–Zehnder interferometric quadrature microscopy

Label-free microscopy enables the visualization of biological structures without stains or labels, but few techniques can image thick, unprocessed tissue with molecular-specific contrast. Photoacoustic microscopy (PAM) provides label-free absorption-based contrast in reflection mode but requires contact through an acoustic coupling medium. Photoacoustic remote sensing (PARS), a non-contact variant, maps optical absorption contrast through intensity changes in an interrogation beam co-focused with the excitation beam. Despite the high sensitivity of interferometric methods, PARS adopts a non-interferometric scheme to avoid the instability and sensitivity fluctuations traditionally associated with interferometry. Here, we present Absorbance Mach–Zehnder Interferometric Quadrature (AMAZE-IQ or simply AMAZE) microscopy, which leverages interferometric detection with robust signal recovery enabled by passive optical quadrature detection. This approach enables simultaneous detection of amplitude and phase modulations of the interrogation beam following an excitation pulse. Unlike conventional interferometric systems, it requires no active stabilization or vibration isolation. Using ultraviolet excitation (UV-AMAZE), we demonstrate label-free imaging of cell nuclei in both fresh, unprocessed and formalin-fixed paraffin-embedded (FFPE) tissues. In fresh mouse tissue, UV-AMAZE achieved up to a 24 dB improvement in signal-to-noise ratio over UV-PARS. Additionally, AMAZE provided absorption contrast in thin metal targets through phase modulation, which PARS struggled to achieve. With its high sensitivity and reflection-mode operation, AMAZE opens possibilities in label-free absorption imaging, including slide-free virtual histology and non-destructive testing.