Fresnel zone plates (FZPs) are widely used for X-ray focusing and imaging thanks to their compactness and high resolution compared to refractive or mirror-based X-ray optics. However, achieving high diffraction efficiency—especially in the hard-X-ray regime—requires FZPs with extremely high aspect-ratio zone structures (i.e., narrow outer zone widths and large thickness) so that sufficient interaction with the X-ray beam occurs. Fabrication limitations (e.g., collapse of deep nanostructures and absorption losses) impede the production of single FZPs that combine both high resolution and high efficiency.
One practical approach is to stack two or more FZP chips in close optical alignment, effectively increasing the optical thickness while preserving resolution. Nevertheless, stacking introduces severe alignment challenges—lateral (x,y), rotational, tilt/yaw—especially in the near-field regime of the optics. Traditional alignment methods often rely on X-ray probing, mechanical contact, or moiré-based metrology with limited degrees of freedom or friction-induced errors. Therefore, there is a need for a contactless, high-precision alignment method that handles multiple degrees of freedom and suits FZP stacking for high-efficiency X-ray optics.
To overcome these limitations, the research team led by Prof. Jinyang Liang at the Institut National de la Recherche Scientifique (INRS) – Université du Québec invented the Double-Illumination All-Optical Nanoalignment (DIANA) technique in a collaboration with Applied Nanotools Inc. The DIANA system operates using two complementary illumination modes (Fig. 1). In reflection, a coherent laser beam detects angular deviations such as tilt and yaw through interference patterns. In transmission, an incoherent light source images micro-patterned reference gratings integrated into each chip, allowing lateral and rotational adjustments with nanometre sensitivity. By analyzing optical fringes in real time, the system automatically guides piezo-controlled stages to achieve full five-degree-of-freedom alignment.
The system was used to align two independently fabricated gold FZP chips, each patterned on a silicon-nitride membrane and supported by a silicon frame. The top and bottom chips were engineered with concentric diffractive zones and embedded alignment gratings (Fig. 2), fabricated by electron-beam lithography followed by electroplating. The chips also include Vernier-scale features and moiré gratings positioned near the edges to enable optical detection of lateral and angular misalignments during stacking.
The alignment process proceeds in two main steps. First, a coherent reflection beam is used to correct angular misalignments: interference fringes generated by reflections from the two zone-plate surfaces reveal differences in tilt and yaw, which are iteratively minimized until the fringes disappear, indicating parallelism. Second, an incoherent transmission beam is employed to refine lateral and rotational alignment. The overlapping alignment gratings on the two chips produce moiré patterns whose displacement encodes the relative x–y position and in-plane rotation. By analyzing these moiré fringes in real time, the system drives piezoelectric actuators to bring the two zone plates into coincidence with sub-30-nanometer precision, completing full five-degree-of-freedom optical alignment without mechanical contact (Fig. 3).
In summary, this paper presents a novel alignment technique, DIANA, that enables the precise stacking of two X-ray FZPs with alignment tolerances in the tens of nanometres laterally and ~100 µrad rotationally, all achieved optically without mechanical contact. By combining laser‐interferometric tilt/yaw correction via coherent reflection illumination with Vernier/moiré-based lateral/rotational alignment via incoherent transmission illumination, they address the key challenges of FZP stacking—namely, high-precision positioning in multiple degrees of freedom and avoiding friction or damage due to chip contact. The demonstration marks a significant step toward making stacked-FZP optics feasible for high-efficiency X-ray imaging. Looking ahead, the authors envision integrating DIANA into a nanofabrication facility for stable mass production of high-diffraction-efficiency stacked FZPs. The outlook suggests that this alignment technology will open new opportunities in X-ray nanofocusing, microscopy, and other fields requiring precise diffractive‐optic stacking.