Optical elements in gas sensors

A method of preventing, removing or reducing condensation on an optical element in a gas sensing apparatus, wherein the gas sensing apparatus comprises a gas sensor arranged to use light to sense presence of a gas and wherein the optical element is arranged so that said light impinges thereon, the method comprising:

• using a thermoelectric heat pump to transfer heat energy to the optical element, wherein:
• the thermoelectric heat pump has a cold side and a hot side, and the thermoelectric heat pump transfers heat energy from said cold side to said hot side in response to a supply of electrical energy provided to the thermoelectric heat pump;
• the hot side of the thermoelectric heat pump is in thermal contact with the optical element;
• the gas sensing apparatus comprises a heat sink in thermal contact with the cold side of the thermoelectric heat pump;
• and
• the heat sink is disposed in the measurement volume.