10 IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, VOL. 51, NO. 1, FEBRUARY 2002 A Scanning Laser Microscope System to Observe Static and Dynamic Magnetic Domain Behavior Warwick Clegg, Senior Member, IEEE, David F. L. Jenkins, Na Helian, James F. C. Windmill, Student Member, IEEE, Nick Fry, Ron Atkinson, Senior Member, IEEE, William R. Hendren, and C. David Wright Abstract—Scanning laser microscopes (SLMs) have been used to characterize the magnetic properties of materials for some time. The first SLM built [1] was a purely static system capable of imaging magnetic domains. Dynamic capability was introduced with the development of the R-Theta microscope [2]. However, this microscope utilizes a rotating drive. A scanning laser microscope has been designed to observe the dynamic behavior of domain switching during the thermo-magnetic write process and the subsequent magnetization state (domain orientation) in stationary media, without the requirement for a rotating drive. It will also be used to write to the magneto-optic (MO) disk material thermo-magnetically prior to imaging. Images are derived from the longitudinal and polar magneto-optic Kerr effects. In this paper, the different configurations for imaging are described and some initial images are presented. Index Terms—Data storage, dynamic laser microscopy, mag- neto-optics. I. INTRODUCTION T HE aim of the project is to develop a versatile imaging system that enables the observation of magnetic behavior for a variety of applications. Scanning laser microscopes (SLMs) are extremely well suited for this and are also able to write bits for subsequent imaging with either an SLM or a magnetic force microscope (MFM). While an SLM is able to image at a resolution of (around 250 nm in this case), its writing resolution capability is greater than this limit, as it is principally a thermal process, as opposed to an optical one. The thermal profile of the laser-heated region mirrors that of the optical intensity profile of the laser, but only the central region, where the temperature is above the Curie point ( ), is able to reverse domains. Compared to an SLM (without scanning near-field microscopy—SNOM—capability), an MFM offers high-resolution imaging at the nanometer level, but with a very limited scan area; typically, this is up to 100 100 m. The SLM, however, is able to image a much larger area, up to 10 10 mm in 50 nm increments, by mounting the sample on a precision motorized - sample stage. Wherever possible, the microscope system has been made modular. This enables the imaging system to be flexible and al- lows functions to be added or changed for different applications. Manuscript received May 4, 2000; revised November 12, 2001. W. Clegg, D. F. L. Jenkins, N. Helian, J. F. C. Windmill, and N. Fry are with the Centre for Research in Information Storage Technology, University of Ply- mouth, Drake Circus, Plymouth, U.K. R. Atkinson and W. R. Hendren are with the School of Mathematics and Physics, Queen’s University Belfast, Belfast, U.K. C. D. Wright is with the School of Engineering and Computer Science, Har- rison Building, University of Exeter, U.K. Publisher Item Identifier S 0018-9456(02)02299-4. Fig. 1. Optical pathway for the SLM system. This is also a consideration for future development and appli- cations of the microscope, for example, a scanning near-field magneto-optic module. The scanning laser microscope system is based around a central PC that uses National Instruments LabVIEW software as the user interface and development base. The component parts of the mi- croscope system are controlled and monitored from the computer via both a data acquisition (DAQ) board and other dedicated con- trol cards. The system is now largely complete and experimental testing of a variety of material specimens has begun. II. OPTICAL SYSTEM DESIGN The optical system incorporates both Gaussian beam optics (for beam transformation) and geometric optics (scanning and de-scanning) [3]. To enable the laser beam to both be completely stationary and completely fill the aperture of the final focusing objective, a small amount of beam over-spill is permissible. This is shown schematically in Fig. 1. The output beam from the laser is expanded, spatially filtered, then focused to a 5 m spot at the midpoint of the AO modulator (AOM); the rise time of the AOM is directly proportional to the spot size. Geometric optics is used to image the scan mirror pivot points using relay lenses RL1 and RL2, to image both pivot points (or stationary points) onto the back focal plane of the final focusing objective lens, with unity magnification. Gaussian beam optics are simultaneously used to transform the beam wave fronts to produce a collimated beam at the back focal plane of the final focusing objective lens. A 0018–9456/02$17.00 © 2002 IEEE