Frequency reference set-up with nine-cell iodine glass cell
Light is an electromagnetic wave and has a frequency. Lasers emit light with a stable frequency, but for precise measurements this stability is often insufficient. One method to stabilise laser frequency is to couple it to a well-defined electromagnetic transition of an atom or molecule. A proven medium for this stabilisation is iodine.
A highly precise method for laser frequency stabilisation is Doppler-free modulation transfer spectroscopy. This process requires two counter-propagating laser beams: a pump beam and a probe beam. The pump beam selectively excites iodine molecules. Once the molecules are excited, they cannot absorb any more light at the same frequency. This means that the probe beam remains unaffected, is able to pass through the cell, and is then detected. If the laser frequency changes, the measured signal also changes, allowing it to be used for control purposes. This method enables highly precise frequency stabilisation.
The frequency of a green laser is approximately 283,000,000,000,000 hertz (283 THz). Iodine spectroscopy allows for stabilisation to within one hertz or better. This corresponds to a relative accuracy of 10-15.
Such frequency stabilities are used in many scientific and technical applications, including meteorology, high-precision experiments in quantum optics, and time and frequency measurement. A well-known example is their use in global navigation systems such as Galileo or GPS, which require extremely accurate time measurements for precise positioning.
The exhibit presents a compact iodine stabilisation setup. Here, a laser beam that is normally 90 centimetres long is folded into a compact 10 x 10 centimetre cell through multiple reflections. As such, it has been possible to significantly reduce the size of the setup without compromising the stabilisation efficiency. These findings are being incorporated directly into the design of the COMPASSO project, which is concerned with the development of a high-precision clock for use on board the International Space Station ISS.
Links:
German Aerospace Center (DLR)
Institute of Quantum Technologies
E-Mail contact-dlr@DLR.de
Credits: ©DLR
