Laser cleaning apparatus and method

Laser cleaning apparatus (100) comprising: a laser system (102) configured to output laser light having a power, a wavelength, a temporal characteristic and a divergence; a delivery cable (106) to deliver the laser light to a cleaning head; a cleaning head (110) comprising: an output aperture and output optics (116) configured to focus the laser light (104) to have a fluence at a focal plane (126) that is greater than an ablation threshold of a surface contaminant to be removed from a surface to be cleaned; scanning apparatus (118) to scan the laser light in at least one dimension across a scan region within the focal plane to cause the scanning laser light to have an effective divergence greater than the divergence of the laser light and to have a corresponding safe working distance from the output aperture determined by the effective divergence, the power, the wavelength and the temporal characteristic; and scan monitoring apparatus (120) to monitor the effective divergence of the scanning laser light and to generate an alarm signal (108) in response to determining that the effective divergence has changed.