3D ESR microscopy with micron-scale resolution

Over the last year we have significantly improved upon our capabilities of ESR microscopy. Our previous 2D CW ESR microscope, operating at 9 GHz, was upgraded, and it is now capable of acquiring 3D images with a resolution of ~10×10×30 microns in a few minutes of acquisition at room temperature. These capabilities rely upon the development of an improved miniature resonator, fed via microstrip line, that enhances the ESR signal by a factor of ~2; optimized gradient coils capable of achieving gradients of 5 T/(m·A) which improves by a factor of ~2 upon our previous efforts; and advanced control and imaging software. The mechanical structure of the imaging probe was also revised to enable accurate positioning of the sample with respect to the resonator and gradient coils. The modular design of the system enables us to achieve a microscopy imaging capability in conjunction with any commercial CW ESR spectrometer. The system can acquire the image of a small “optical-like” (~ 1.5×1.5×0.25 mm) sample either by the modulated field gradients method, the projection reconstruction method, or by a combination of the two. In addition, it can acquire spectral-spatial images, where for each pixel in space, the ESR spectrum is obtained. An example of 2D and 3D ESR images, obtained by the new microscope for a small crystal of LiPc radical, is given in the figure. Pulsed imaging methods and elevated frequencies, would extend this technology and enable us to obtain several types of image contrasts with micron-scale resolution.