Ptychography has become a popular technique for high-throughput and high-resolution characterization of 2D/3D materials. When objects introduce significantly large phase shifts, a multi-slice model needs to be considered to account for long-distance wave propagation within the sample. Although many groups have demonstrated multi-slice ptychography using specimens that are several times larger than the depth of field (DOF), the benefits of applying the multi-slice ptychography algorithm on small objects within the DOF is rarely discussed. Here we address this question and demonstrate that multi-slice ptychography can play an important role in improving reconstruction quality for continuous objects that are smaller than the DOF.
As a scanning version of coherent diffraction imaging (CDI), X-ray ptychography has become a popular and very successful method for high-resolution quantitative imaging of extended specimens. The requirements of mostly coherent illumination and the scanning mechanism limit the throughput of ptychographic imaging. In this paper, we will introduce the methods we use at the Advanced Photon Source (APS) to achieve highthroughput ptychography by optimizing the parameters of the illumination beam. One work we have done is increasing the illumination flux by using a double-multilayer monochromator (DMM) optics with about 0.8% bandwidth. Compared with our double-crystal monochromator (DCM) optics with 0.01% bandwidth, this DMM optics provides around 20 times more flux. A multi-wavelength reconstruction method has been implemented to deal with the consequential degraded temporal coherence from such an illumination to ensure high-quality reconstruction. In the other work, we adopt a novel use of at-top focusing optics to generate a at-top beam with the diameter of about 1.5 μm on the focal plane. The better uniformity of the probe and the large beam size allow one to significantly increase the step size in ptychography scans and thereby the imaging efficiency.
Among different techniques based on x-ray nanoimaging, ptychography has become a popular tool to study specimens at nanometer-scale resolution without the need of using high-resolution optics that requires very stringent manufacturing processes. This high-resolution imaging method is compatible with other imaging modalities acquired in scanning microscopy. At the Advance Photon Source (APS), we have developed two fluorescence microscopes for simultaneous ptychography and fluorescence imaging which together provide a powerful technique to study samples in biology, environmental science, and materials science. Combined with different tilted sample projections, such correlative methods can yield high-resolution 3D structural and chemical images. More recent work has been focused on the development of a fast ptychography instrument called the Velociprobe which is built to take advantage of the over 100 times higher coherent flux provided by the coming APS upgrade source. The Velociprobe uses high-bandwidth accurate interferometry and advanced motion controls with fast continuous scanning schemes which are optimized for large-scale samples and 3D high-resolution imaging. This instrument has been demonstrated to obtain sub-10 nm resolution with different high-photon-efficient scanning schemes using fast data acquisition rate up to 3 kHz (currently limited by detector's full continuous frame rate). A ptychographic imaging rate of 100 _m2/second with a sub-20 nm spatial resolution was shown in this paper.
X-ray ptychography has become a standard technique for imaging materials at <10 nanometer spatial resolution. Recent developments have shown its potential in obtaining quantitative images of the 2D/3D structure of large objects at millimeter and centimeter-scale, which requires not only new instrumentation and experiment design, but high-throughput workflow for data processing. At Argonne’s Advanced Photon Source, we imaged an integrated chip with over 600 × 600 µm^2 field of view at sub-20 nm spatial resolution and achieved 3000 Hz data acquisition rate with advanced motion control. Here, we discuss challenges in achieving large-area reconstruction and explore strategies for streamlining data processing. We demonstrate a novel data acquisition scheme that combines the merits of both step scan and (continuous) fly scan. Inaccurate scan position and large beam variation also degrade image quality and need to be corrected during reconstruction.
In high power laser systems, crystal defects introduced by manufacturing have significant impact on quality of light beams; finally affect the output status of high power laser system. The phase retrieval algorithm can precisely measure the crystal defects, such as the residual periodic perturbations in a relatively large area and the relatively small point defects, with the resolution of micrometer magnitude. At the same time, the multiple near-focus intensity measurements algorithm used here can retrieve the morphology of focal spot, which is modulated by the defects and cannot be directly measured due to its high power. In addition, the algorithm has been improved in order to use less measurement planes and less iteration times to complete retrieval.
KEYWORDS: Laser damage threshold, Laser induced damage, Optical components, Near field optics, Thin films, Laser sources, Superluminescent sources, Near field, High power lasers, Modulation
An accurate evaluation method with an amplified spontaneous emission (ASE) as the irradiation source has been developed for testing thin-film damage threshold. The partial coherence of the ASE source results in a very smooth beam profile in the near-field and a uniform intensity distribution of the focal spot in the far-field. ASE is generated by an Nd: glass rod amplifier in SG-II high power laser facility, with pulse duration of 9 ns and spectral width (FWHM) of 1 nm. The damage threshold of the TiO2 high reflection film is 14.4J/cm2 using ASE as the irradiation source, about twice of 7.4 J/cm2 that tested by a laser source with the same pulse duration and central wavelength. The damage area induced by ASE is small with small-scale desquamation and a few pits, corresponding to the defect distribution of samples. Large area desquamation is observed in the area damaged by laser, as the main reason that the non-uniformity of the laser light. The ASE damage threshold leads to more accurate evaluations of the samples damage probability by reducing the influence of hot spots in the irradiation beam. Furthermore, the ASE source has a great potential in the detection of the defect distribution of the optical elements.
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