Although Kerr contrast can in theory be infinite, the combination of multiple polarization aberration effects often significantly reduces the polarization purity. Consequently, conventional Kerr microscopes regularly report Kerr contrasts that are barely detectable. One such aberrative effect arises from the use of broad spectrum light sources. As the amount of polarization rotation induced by the magneto-optical Kerr effect is inversely proportionate to the wavelength of light used, conventional broadband sources generate light polarization with the same broad spectrum.
In other words, the light polarization is no longer perfectly linear and the observed magnetic contrast is severely reduced.
To overcome this form of aberration, several light sources were tested and ultimately, an ultrabright LED with a FWHM of 50 nm was used. Owing to the narrow bandwidth light source, the amount of polarization rotation in the reflected light is also narrowly spread, allowing for a strong magnetic contrast.
OPTIMISED LIGHT PATH DESIGN
Every optical component used, be it lenses or beamsplitters, causes a minute amount of polarization rotation. In the worst case, the polarization is rotated in a spatially non-uniform way that cannot be compensated for easily. The MagVision Kerr microscope uses an optimized light path design to reduce the unwanted polarization aberrations.
Electromagnet design for Kerr microscopy is traditionally a challenging topic where several tradeoffs must be made. Due to the requirement of a high imaging resolution, large objectives must be placed closed to the sample surface.
This imposes a spatial constraint on the electromagnet and limits the magnetic field strength generated. Secondly, much of the magnetic flux permeates into the objectives and results in the Faraday rotation of the polarized light, greatly reducing the contrast.
Our revolutionary electromagnet design circumvents both problems with an innovative closed-flux design. By trapping the magnetic field within the electromagnet, the maximal field strength is increased by a factor of 4 while the objective experiences 8 times less magnetic field. The perpendicular field uniformity is also top-of-class at 0.5% over 4 millimeter.
The vastly improved performance removes the need for noisy and expensive water cooling.
For digital microscopy, the camera is arguably the most important part. This is further compounded by the fact that Kerr microscopy only allows for less than a hundredth of the incident light to reach the sensor, due to the extinct polarizers. Therefore, we have hunted for and found the perfect camera for such a task, a state of the art CMOS back-illuminated sensor with 20 megapixels. Not to mention, our imaging sensor reaches a quantum efficiency of 83% at our light source wavelength.
As scientists ourselves, we fully understand the pains of performing long and repetitive measurements. That is why we have designed an easy-to-use scripted experiment designer. The powerful for-loop structure allows for multiple parameter sweeps, be it magnetic field pulses or current pulses. Even for a simple experiment, it becomes easy to collect statistical data with just a few lines. Furthermore, the software controllable XYZ positions ensure that stage drift is eliminated for completely non-supervised experiments.
Our microscope comes with 10-pin chip carrier that interfaces with the sample stage via spring-loaded pogo pins. This means that samples and devices can be swapped easily.
MagVision is also compatible with micromanipulators for DCF probing.