Abstract: Matrix-assisted laser desorption/ionisation mass spectrometry imaging (MALDI-MSI) apparatus and method comprising a laser and a multimode optical fiber to deliver a laser beam to a MADLI ion source. A vibration coupling is provided at a region along the length of optical fiber to impart an oscillatory vibrational motion at the optical fibre to move the irradiation intensity maxima at the sample to increase the effective irradiation surface area. The present apparatus and method provide increased imaging sensitivity and a corresponding reduction in data acquisition times.