1. Field
The present subject matter relates to an optical pumping magnetometer and a magnetic sensing method.
2. Description of Related Art
As highly sensitive magnetic detection methods, optical pumping magnetometers have been proposed which use electron spin of alkali metal vapor.
Applied Physics B has disclosed an optical pumping magnetometer for detecting a magnetic field with the use of variation in Larmor frequency in a glass cell containing cesium.
In this optical pumping magnetometer, the electron spin motion of cesium vapor is caused by the oscillating magnetic field applied from an excitation coil, and changes the absorption of laser light passing depending on the orientation of spin polarization. The intensity of the transmitted laser light is detected by a photo-detector to obtain a signal that changes at the same frequency as the oscillating magnetic field. Attention is focused on the phase difference between the signal from the photo-detector and an electrical signal supplied to the excitation coil in order to generate the oscillating magnetic field to read the variation in Larmor frequency, and measure a magnetic field generated from an object to be measured.
In the optical pumping magnetometer of the conventional example described above, the transverse relaxation time T2 of the electron spin of the alkali metal vapor is a proportionality coefficient between the phase difference and the variation in Larmor frequency, and the response of the magnetometer with respect to the magnetic field generated from the object to be measured is thus improved as the transverse relaxation time is longer.
However, the conventional example has a problem that the response of the magnetometer is not improved even when the transverse relaxation time is increased in the case of measuring a variable magnetic field with a shorter variation period of the magnetic field generated from the object to be measured, as compared with the transverse relaxation time of the electron spin of the alkali metal vapor.