A system comprising: a laser diode array comprising: a plurality of laser diodes (201 - 210), wherein the laser diodes are configured to emit electromagnetic radiation having the same centre wavelength at different respective junction temperatures; and a channel proximate to each of the laser diodes, the channel configured to receive and provide a passage for a flow of a fluid coolant; a coolant inlet and a coolant outlet , through which the fluid coolant may flow; a coolant supply system coupled to the laser diode array and configured to cause a fluid coolant to flow through the channel of the laser diode array; an input temperature sensor configured to measure a temperature of the fluid coolant input to the laser diode array; wherein the coolant supply system is configured to control a supply of the fluid coolant to the laser diode array dependent on sensor measurements by the input temperature sensor, wherein the coolant supply system is configured to, using sensor measurements by the input temperature sensor, supply the fluid coolant to the laser diode array, the supplied fluid coolant having a temperature substantially equal to the junction temperature of a laser diode that is closest to the coolant inlet of the laser diode array; H an output temperature sensor configured to measure a temperature of the fluid coolant output from the laser diode array, wherein the coolant supply system is configured to, using sensor measurements by the output temperature sensor, control a flow rate of the fluid coolant to the laser diode such that the temperature of the coolant output from the laser diode array is substantially equal to the junction temperature of a laser diode that is closest to the coolant outlet of the laser diode array. a plurality of laser diodes (201 - 210), wherein the laser diodes are configured to emit electromagnetic radiation having the same centre wavelength at different respective junction temperatures; and a channel proximate to each of the laser diodes, the channel configured to receive and provide a passage for a flow of a fluid coolant; a coolant inlet and a coolant outlet , through which the fluid coolant may flow; a coolant supply system coupled to the laser diode array and configured to cause a fluid coolant to flow through the channel of the laser diode array; an input temperature sensor configured to measure a temperature of the fluid coolant input to the laser diode array; wherein the coolant supply system is configured to control a supply of the fluid coolant to the laser diode array dependent on sensor measurements by the input temperature sensor, wherein the coolant supply system is configured to, using sensor measurements by the input temperature sensor, supply the fluid coolant to the laser diode array, the supplied fluid coolant having a temperature substantially equal to the junction temperature of a laser diode that is closest to the coolant inlet of the laser diode array; H an output temperature sensor configured to measure a temperature of the fluid coolant output from the laser diode array, wherein the coolant supply system is configured to, using sensor measurements by the output temperature sensor, control a flow rate of the fluid coolant to the laser diode such that the temperature of the coolant output from the laser diode array is substantially equal to the junction temperature of a laser diode that is closest to the coolant outlet of the laser diode array. <EOS>