Hydrogen maser
A hydrogen maser clock is a maser type using the specific properties of the hydrogen atom to serve as a highly accurate frequency standard.
Both the proton and the electron of the hydrogen atom have spins. The atom has a higher energy, when both pins are parallel and have a lower energy when the spins are anti- parallel. The energy required to reverse the spin of the electron, corresponds to a photon of frequency 1420405752 Hertz (Hz). This 1420 MHz frequency is important for radio astronomy, since it corresponds to the 21- cm line of interstellar hydrogen.
Hydrogen maser are very complex devices and sell for around $ 235,000.
There are two types: active and passive.
In both types of exits from a small reservoir controlled molecular hydrogen in a discharge tube made of. Hydrogen molecules are composed of two atoms, which are bonded together. The molecules are cleaved in the discharge tube by an arc discharge in individual hydrogen atoms. This atomic hydrogen passes through a collimator and a selection device for the magnetic state. The atoms are filtered according to the desired state and routed into the storage flask. The accumulator piston is made of quartz and approximately 20 cm high and 10 cm in diameter. Its inner wall is coated with Teflon, is thereby prevented, that the atomic state changes in the collision with the wall. Thus, the recombination of hydrogen atoms into hydrogen molecules is slowed. The Teflon coating is durable and allows operation over 20 years. The accumulator piston in turn is located in a microwave resonator of a precisely manufactured cylinder of copper or silver-coated ceramic. This cavity is tuned to the 1420 MHz resonance frequency of the atom. A weak static magnetic field of a magnet coil is applied in parallel to the cylinder axis, for splitting the magnetic Zeeman levels. In order to suppress the influence of external magnetic fields on the frequency of the resonator is surrounded by several layers of shielding.
In the active hydrogen maser cavity oscillates itself This is a higher hydrogen density and a higher quality factor for the cavity ahead. In high-quality microwave resonators made of silver- coated ceramics, however, the increase factor is much higher, so that a lower hydrogen atom density is required. The active grain is more complex and more expensive, but has better short-term and long-term frequency stability. The model CH1 75 of the PTF for example, at a power of 100 W, a mass of 90 kg. His long-term frequency accuracy is about ± 5 × 10-16 in five years. The model iMaser 3000 has a better short-term stability of 1.2 × 10-13 at a second and a very low phase noise of -130 dBc / Hz at 1 Hz with a 5 MHz reference. The intrinsic frequency drift is 7 × 10-16 per day low even without automatic tuning of the cavity. When used as a clock which is a deviation of 1 second in 63 million years. Through network technology, a new generation of active maser can be easily monitored, controlled and maintained.
In passive hydrogen maser frequency of 1420 MHz is radiated into the cavity from an external source. The external source is tuned to maximum resonance. This allows a lower hydrogen density and a lower quality of the resonator and thus lower costs. The model CH1 76 of the PTF at a power of 90 W, a mass of 55 kg. His long-term frequency stability is much worse than that of the active maser with ± 1.5 × 10-12 per year.