Fig. 2

a Simulation of the aberrated beam field intensity when scatterers are positioned at the centre of the beam path. Four scatterers were modelled, denoted as S1–S4. The scatterers had a diameter of 2 μm and a refractive index of 1.5. 3D rendering of the beam field and the transverse intensity distributions show that the aberration introduced by an individual scatterer is confined within each mode. Z indicates the beam propagation direction. Scale bar: 10 μm. b Photograph of the completed 2.6-F rapid guidewire exchange coronary catheter. c A photograph of the distal end of the catheter, taken using a microscope. The fibre probe had a diameter of 500 μm and a rigid length of less than 4 mm. Scale bar: 500 μm. d Photograph of the ring pattern of the light transmitted through the catheter’s fibre probe optics, corresponding to multiple propagation modes. The screen was positioned at a small angle with respect to the beam propagation direction, showing that the cylindrical mirror directs the beam at an ~8° angle normal to the sheath to reduce specular reflection. e Simulation of the normalised on-axis field intensity distribution with respect to depth for the centre wavelength and the two ends of the spectra, showing that the chromatic focal shift effect mitigated the field intensity discontinuity.