An apparatus comprising a mid-infrared, MIR, imaging system comprising: a MIR laser that is configured to generate a first light beam; a stage (17, 22, 57, 66) adapted to carry a specimen (16, 65) to be scanned; an optical assembly comprising a scanning assembly comprising a focusing lens (15, 25, 55) and a mirror (12, 56), the mirror being arranged to reflect or transmit light from the MIR laser to the focusing lens, which is arranged to focus light at a point on said specimen; a first light detector that is configured to measure first intensities of light leaving points on said specimen during scanning; a stage actuator assembly that is configured to cause said specimen to move relative to said point in a direction so that the point moves across the specimen; a controller (19, 29, 39, 61) that is configured to form a MIR image from said first detected intensities at a plurality of points on said specimen; and a beam intensity detector that is configured to measure an intensity of said first light beam, wherein the focusing lens is configured to focus said first light beam reflected or transmitted by the mirror to said point, the scanning assembly is configured to move in a first direction relative to said stage, whereby said focusing lens is maintained at a fixed distance to said stage, said stage actuator assembly being configured to move said stage in a direction orthogonal to said first direction, wherein said MIR laser is a pulsed light source, said controller is connected to the beam intensity detector and is configured to sum measured intensities from the same point on the sample detected by said first light detector only during periods in which said measured beam intensity, measured by the beam intensity detector, is greater than a first threshold. a MIR laser that is configured to generate a first light beam; a stage (17, 22, 57, 66) adapted to carry a specimen (16, 65) to be scanned; an optical assembly comprising a scanning assembly comprising a focusing lens (15, 25, 55) and a mirror (12, 56), the mirror being arranged to reflect or transmit light from the MIR laser to the focusing lens, which is arranged to focus light at a point on said specimen; a first light detector that is configured to measure first intensities of light leaving points on said specimen during scanning; a stage actuator assembly that is configured to cause said specimen to move relative to said point in a direction so that the point moves across the specimen; a controller (19, 29, 39, 61) that is configured to form a MIR image from said first detected intensities at a plurality of points on said specimen; and a beam intensity detector that is configured to measure an intensity of said first light beam, wherein the focusing lens is configured to focus said first light beam reflected or transmitted by the mirror to said point, the scanning assembly is configured to move in a first direction relative to said stage, whereby said focusing lens is maintained at a fixed distance to said stage, said stage actuator assembly being configured to move said stage in a direction orthogonal to said first direction, wherein said MIR laser is a pulsed light source, said controller is connected to the beam intensity detector and is configured to sum measured intensities from the same point on the sample detected by said first light detector only during periods in which said measured beam intensity, measured by the beam intensity detector, is greater than a first threshold.