JPH0315779A - Magnetism detector - Google Patents

Abstract

PURPOSE:To detect a change in magnetic flux with a high sensitivity and high S/N by introducing the magnetic flux into the resonator of a laser and utilizing a change in the frequency of the light oscillated by a Zeeman effect. CONSTITUTION:The detector is so formed that the magnetic flux 1 of a magnetic flux density B is applied perpendicularly to the light emission axis of the laser 3 of the semiconductor laser 2. This laser 2 emits the light of the frequency corresponding to an energy level difference as the electrons in atoms transfer from the high energy level to the low energy level. The magnetic field by the magnetic flux 1 introduced into the light emitting part, i.e., the resonator of the laser 2 is cloven and changed in the energy level by the Zeeman effect. The degree of the change in the energy level corresponds to the intensity of the magnetic field. The change in the frequency of the light corresponding to the intensity of the magnetic field is, therefore, obtd. and since this change is sensitive to the magnetic field, the magnetic flux is detected with the high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic detector used in magnetic disk devices, magnetic tape devices, etc. [Conventional technology] Conventional magnetic detectors include those that utilize induced electromotive force by a coil, those that utilize magnetoresistive effect, those that utilize Hall effect, and those that utilize magnetically sensitive transistors. Recently, the idea of a quantum magnetometer using high-temperature superconductors has also been proposed. The induction type, magnetoresistive type, and Hall effect type all have a proven track record, and their performance has steadily improved as a result of steady improvements. Japanese Patent Publication No. 58-220
The magnetically sensitive transistor described in No. 239 is intended to have even higher sensitivity, and research is being conducted to put it into practical use. However, for example, in magnetic disk drives, the ability to read recorded signals is insufficient rather than the ability to record magnetic information on the magnetic recording film, and although it has the potential to dramatically increase recording density, it is not fully utilized. Not yet. Therefore, it is desired to improve the sensitivity of the detector and reduce the S/N. On the other hand, the Ryuko fluxmeter has very good sensitivity, but it still requires considerable improvement in terms of its use of superconductivity before it can be put into practical use. [Problems to be Solved by the Invention] The purpose of the present invention is to provide a magnetic detector that has both high sensitivity and practicality, which are common problems of the above-mentioned conventional technologies. [Means for Solving the Problems] In order to achieve the above object, the present invention guides magnetic flux into the resonator of a laser such as a semiconductor laser, and utilizes the change in oscillation optical frequency due to the Zeeman effect to increase the magnetic flux. It is designed to detect changes. A method of applying a magnetic field to a resonator such as an Hθ-Ne laser is often used to create a single longitudinal mode and stabilize the wavelength of the laser. For details, see Applied Physics Vol. 47, No. 5 (1978), p. 432, r Internal mirror type H
``Single longitudinal mode and wavelength stabilization of e-Ne laser using transverse magnetic field''. This utilizes the fact that the oscillation light frequency changes due to Zeeman separation of the amplification medium in the laser due to the magnetic field. For example, normal He
-The internal mirror of the Ne laser has in-plane anisotropy, so
The oscillated light is linearly polarized in this direction or in a direction perpendicular to this direction. On the other hand, in a He-Na laser called a transverse Zeeman laser, one of these anisotropic orientations is aligned with the direction of the transverse magnetic field, so the optical path of the laser resonator includes a transverse magnetic field in addition to the internal mirror. The induced anisotropy of the laser medium is added. If these anisotropies are birefringent, the optical path length between the resonators will be slightly different for the horizontal and vertical vibration components, and two horizontal and vertical polarizations will occur within a single longitudinal mode. The two components will oscillate simultaneously with a slight frequency difference. The Zeeman separation frequency Δf due to such a transverse magnetic field is Δf=1.
4gB [MHz] Here, g is Land's factor and B is the magnetic flux density (Gauge). g is 1-2
Since the value of L, (D is taken, Δf is generally Δf − B [MHz]. In other words, the oscillation optical frequency change on the order of I MHz can be obtained by the I Gaussian magnetic flux density. This also applies to semiconductor lasers. The same can be said.By detecting this oscillation light frequency change as an interference beat signal with another reference light, it is possible to detect changes in magnetic flux density.Originally, between the reference light and the magnetic flux detection light If there is an optical frequency difference of ω, and if the optical frequency change due to the change in magnetic flux density is Δω, then
The beat signal is FM modulated from ω to ω+Δω depending on the presence or absence of a magnetic field. Therefore, by detecting this beat signal with a photodetector or the like and using the principle of FMtxll, changes in magnetic flux can be detected. [Operation] A laser emits light at a frequency corresponding to this energy level difference when electrons within an atom transit from a higher energy level to a lower energy level. The magnetic field introduced into the light emitting part, that is, the laser cavity, splits and changes the above energy level due to the Zeeman effect. The degree of change in energy level corresponds to the strength of the magnetic field. Therefore, it is possible to obtain a change in the frequency of light depending on the strength of the magnetic field. This frequency change is expressed as Δf [MHz] = B [Gau
Since it is sensitive to g+1, highly sensitive magnetic flux detection is possible.
FM demodulation technology can be applied by interfering light whose frequency changes with light of another stable frequency and detecting the frequency change as a beat signal that appears in the interference light intensity.
/N Can detect magnetic flux changes well. [Examples] Examples of the present invention will be described below. The first @ shows the principle structure of the present invention when a semiconductor laser is used. A magnetic flux 1 having a magnetic flux density B is applied perpendicularly to the emission axis of the laser beam 3 of the semiconductor laser 2. When detecting magnetically recorded information in a magnetic disk device or the like, a ring-shaped magnetic pole 4 is opposed to a magnetic recording film 5, as shown in FIG. 2, and a part of the ring is replaced with a semiconductor laser. Of course, the method of guiding magnetic flux to a semiconductor laser is not limited to this ring-shaped magnetic pole, and various magnetic pole structures such as a single magnetic pole head can be used. Figure 3 shows how the obtained light is transferred to the mirror 8 and the beam splinter 9.
The polarizer 10 interferes with the light emitted from the reference semiconductor laser 7, and the photodetector 11 detects a beat signal. It is preferable to control the temperature of the semiconductor laser used here to prevent single mode oscillation from mode hopping. According to this embodiment, since a semiconductor laser is used, the magnetic flux detection unit can be miniaturized. In FIG. 4, a half mirror 12 having optical anisotropy is used as the outer alt of a semiconductor laser, and two types of light having vibration planes in the horizontal and vertical directions are oscillated. This semiconductor laser has a magnetic flux l
and transition the frequency. The amount of transition of this frequency is 2
Since it differs depending on the type of light, the frequency difference between these two types of light changes depending on the magnetic flux. Therefore, by interfering these two types of light with the polarizer 10 and detecting the beat signal with the photodetector 11, changes in magnetic flux can be detected. According to this embodiment, since two types of light from one semiconductor laser are used, the components of the detector can be simplified, and temperature control to suppress mode hopping in a single mode can be easily carried out, making detection possible. It has the effect of being stable. [Effects of the Invention] According to the present invention, changes in magnetic flux can be detected as changes in the frequency of the laser beam and also as changes in the frequency of the beat signal due to interference with the reference beam, so changes in magnetic flux can be detected with high sensitivity and high S/N. Can be detected.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the basic structure of a magnetic detection fence according to an embodiment of the present invention, FIG. 2 is a perspective view of an embodiment incorporating a magnetic detection head for a magnetic recording medium, and FIG. FIG. 4 is a perspective view of an optical system of an embodiment that detects a frequency change of frequency modulated light as an interference beat signal with a reference light.
FIG. 2 is a perspective view of an optical system showing an example of oscillating light with two types of polarized light from one semiconductor laser and detecting magnetic flux from the difference frequency. DESCRIPTION OF SYMBOLS 1... Magnetic flux, 2... Semiconductor laser, 3... Laser light, 4... Magnetic pole, 5... Magnetic recording film, 6... Base, 7... Semiconductor laser for reference, 8 ...mirror, 9
...beam splitter. 10...Polarizer, 1 piece...
・Photodetector, Whisper diagram name 2 Figure) t 3 Interceptor 4 Of course

Claims (1)

[Claims] 1. A magnetism system characterized by guiding a magnetic flux into a laser resonator and detecting changes in the oscillation frequency of light caused by the Zeeman effect due to this magnetic flux. Detector. 2. Claim 1, wherein the laser is a semiconductor laser
Magnetic detector described in section. 3. A magnetic head, characterized in that the magnetic detector according to claim 1 or 2 is mounted on a floating slider to detect magnetically recorded information. 4. The magnetic flux according to claim 1, wherein the laser beam whose frequency has been changed by the magnetic flux is caused to interfere with another stable laser beam, and the magnetic flux is detected from the change in the bead frequency that appears in the intensity of the interference light. Detector. 5. The magnetic detector according to claim 1, wherein a single mode oscillation laser beam is used as the laser beam. 6. The magnetic detector according to claim 1, wherein the magnetic flux is guided so as to act parallel to the oscillation axis of the laser resonator. 7. The magnetic detector according to claim 1, wherein the magnetic flux is guided so as to act perpendicularly to the oscillation axis of the laser resonator. 8. A magnetic detector comprising the magnetic flux detection laser according to claim 1 and a stable frequency laser whose oscillation frequency is different from that of the laser. 9. Provide optical anisotropy to the internal mirror or appropriate external mirror on the end face of the laser resonator, oscillate two types of light with vibration planes parallel or perpendicular to this anisotropy, and create this optical anisotropy. Direct the magnetic flux parallel or perpendicular to the direction of the
A magnetic detector characterized by detecting changes in different types of oscillated light. 10. A magnetic detector according to claim 9, characterized in that two orthogonal types of light are caused to interfere with each other, and a change in magnetic flux is determined from a change in a beat signal that appears in the intensity of the interference light.