Fig. 1

Principle of motionless SIR-PAM. a Principle of spatially invariant resolution photoacoustic microscopy (SIR-PAM). To achieve spatially invariant resolution volumetric imaging, SIR-PAM uses PISFs to stimulate PA signals within an object and extract its Fourier spectra, and uses an ultrasonic transducer to resolve the depth of the PA signals. b Principle of conventional PAM. A focused Gaussian beam is utilized in conventional PAM to stimulate PA signals, restricting its DOF. Besides, conventional PAM uses raster scanning to realize volumetric imaging. An object with uniformly distributed microparticles was simulated to compare the image qualities of two methods. c PSFs of SIR-PAM (red curve) and conventional PAM (blue curve), which indicate that SIR-PAM achieves 1.5 times finer lateral resolution than conventional PAM. Scale bars, 100 µm