A team in New Mexico University has created the first-ever optical cryocooler that could be applied to airborne and spaceborne sensors. It uses optical refrigeration which could enable miniaturization, an alternative to bulky mechanical cryocoolers. The principle underlying optical refrigeration may sound paradoxical: to lower the temperature by shining laser light on it. But the materials used are highly fluorescent: after the laser radiation the heat is carried away from the material via the fluorescence. The earliest experiments at Los Alamos, New Mexico, back in 1995, led to about 1 degree cooling. Thanks to subsequent improvements, an absolute temperature of 208 K (-65°C) was reached. But more recent improvements led to a new milestone of 155 K (-118°C). Several factors contributed to this success, such as the use of extremely pure materials and a better insight into the physics of luminescent crystals. Pure crystals containing ytterbium ions were used for example. Ytterbium is an element from a group known as the rare earths that are extremely efficient in their fluorescence essential for optical refrigeration. Further developments may lead to applications in cooling superconducting electronics, infrared and gamma-ray sensors. Many other applications requiring miniaturized cryocoolers could benefit from this technology. An alternative recent development of laser cooling (initially proposed in 1978 by researchers from New York and Helsinki) was developed in the University of Bonn. It implied changing the orbit of electrons thanks to laser light. In order to stay on a higher orbit, the electrons required thermal energy. Researchers from Bonn then heated a mixture of argon gas with traces of rubidium to 350°C at a pressure of 230 bars. Under those conditions, the gas mixture cooled down by almost 70°C within several seconds. It is hoped this technology could ultimately lead to the creation of mini fridges.