Patent GB-839406-A (GB)
IPC: H01S1/02
Abstract: 839,406. Masers. WESTERN ELECTRIC CO. Ltd. Oct. 25, 1957 [Oct. 29, 1956], No. 33395/57. Class 40 (9). A substance for use in apparatus utilizing electron spin resonance comprises an insulating material having a concentration of localized imperfections introduced by radiation damage whereby it is paramagnetic. The substance may be used either in a maser or in a spinecho storage device. As described the substance may be an alkali halide such as sodium or potassium chloride, which has been bombarded, e.g. by electrons, neutrons or X-rays, thereby providing displacements and vacancies in the lattice structure. Where an anion is displaced and the vacancy is occupied by an electron (to provide an " F-centre ") this electron can be exploited for the above-mentioned purposes. In the maser device shown, the crystal 22, so treated, is situated in a waveguide 21 and surrounded by a magnetizing coil 23 fed from a source 24. Energy for providing a " negative temperature " distribution for the spin states is provided by the source 25. When this distribution is established the signal to be amplified is applied from source 27, the amplified signal being fed to a load 28. After the application of the signal for amplification a " thermatizing interval " is allowed to allow sufficient relaxation to ensure that the next energy burst is effective to ensure a " population inversion " i.e. to establish a negative temperature distribution. A synchronizing circuit 29 controls the alternate application of energy from source 25 and input signals from source 37 and the provision of the thermatizing interval. The operating frequency is controlled by the strength of the magnetizing current. The portion of the waveguide in question should be kept at the temperature of liquid helium. A gate may be provided at the output of the waveguide to prevent energy-from the source 25 reaching the load. Amplification may take place of an input signal whose frequency differs from that of the energy providing source 25. Thus, after the negative temperature state is established by the source 25, the magnetizing current may be increased (or decreased) under control of the synchronizing circuit 29, thereby increasing (or decreasing) the energy difference between the spin levels with a corresponding change in the frequency of the signal that can be amplified. Instead of using a fixed frequency energy source 25, the frequency of the source may be caused to sweep through over a range, only transitorily coinciding with the frequency required for establishing the negative temperature distribution. Flux changing as described above may also be incorporated in this embodiment. Alternatively a fixed frequency is used for the source 25 and the magnetic flux is caused to sweep through a valve corresponding to spin resonance at the frequency of the source. Here again the negative temperature can be established at one value of the magnetic flux, and amplification at another. Instead of a waveguide a resonant cavity may be used in which case it is desirable that the energizing frequency be different from the signal frequency to prevent ringing. For continuous amplification several such amplifiers may be arranged in parallel and operated in sequence, so that one amplifier is always effective at any given time. The substances described may be used in spin-echo systems of the types described in Specifications 795,057, 798,021 and 816,659.