I. Jong Kim

We report the implementation of temporally modulated scanning illumination to enhance optical sectioning in epi-illumination line-scan confocal microscopy. By applying a sinusoidal intensity modulation with a spatial period set to twice the line beam width, and synchronizing the pixel exposure time to the modulation period via rolling shutter control, our method improves the contrast of in-focus signals while effectively suppressing out-of-focus background fluorescence. We demonstrate enhanced sectioning performance through volumetric fluorescence imaging of three samples with different thicknesses: 15 µm fluorescent beads, a ∼30 µm-thick corn grain section, and a ∼180 µm optically cleared mouse kidney. This simple yet practical approach extends the sectioning capability of conventional epi-illumination line-scan confocal systems without requiring hardware modifications, offering a promising solution for high-contrast three-dimensional imaging of thick biological specimens such as organoids.

High-resolution thermoreflectance microscopy is demonstrated for non-contact nanometer-scale thermal imaging. Optical fibers with sub-wavelength-sized apertures (ϕ = 50 nm) are adopted as optical scanning-probes to overcome the diffraction limit of conventional refractive optical microscopy. The spatial resolution down to 94.2 nm is achieved, clearly resolving thermal distributions of a gold resistive heater with 100-nm-wide lines and spaces. The demonstrated method will provide thermal imaging of advanced electronic devices along with uncompromised spatial resolution as well as high adaptability of wavelength tailored for material-specific thermoreflectance coefficients.

We propose a spiral-phase-contrast imaging system for space optics by integrating a linear astigmatism-free three-mirror system (LAF-TMS) with a spiral phase plate (SPP) in a 4f configuration. The LAF-TMS enables unobscured, off-axis reflective imaging while completely eliminating linear astigmatism across a wide field of view, ensuring robust optical performance suitable for compact space imaging. To enhance phase contrast, we implemented an SPP with a flat central region that maintains a constant phase, generating distinct spiral interference fringes via self-referenced interferometry. These fringes were utilized to reconstruct the 3D topography of a lunar surface-inspired microscale structure, known as the “fairy castle,” which models the fragile, porous features typical of the Moon. Simulations confirmed accurate 3D reconstruction with a root mean square error in the sub-micron range. A Monte Carlo-based tolerance analysis further demonstrated that the required alignment precision is achievable with standard optomechanical components, supporting the system’s feasibility for in-situ implementation in future space missions.

This study presents a straightforward, efficient dual-mode thermoreflectance microscopy (TRM) system for analyzing the stationary and dynamic thermal properties of microelectronic devices. The proposed TRM system employs a standard visible microscope and implements two distinct imaging process schemes to obtain thermal images at different time scales. For TRM imaging of an ohmic microdevice, the optimal probing wavelength is predetermined from the thermoreflectance spectrum, acquired using a white light-emitting diode source and tunable bandpass filters to enhance thermal sensitivity. Thermoreflectance images are obtained in both stationary and transient modes using a four-bucket method and a pulsed boxcar averaging method, respectively. This thermography approach demonstrates highly sensitive, time-integrated stationary thermal imaging and time-gated transient thermal imaging with a temporal resolution of 200 ns. The system shows significant potential as an analytical tool with a sub-micron spatiotemporal resolution for evaluating heat generation and self-heating behavior in microelectronic devices.

The use of vortex laser beams has increased in various areas of optics and photonics, necessitating enhanced beam quality for wide usage. In the field of high-power lasers, a range of methods to implement vortex laser beams has been proposed. Nonetheless, enhancing beam quality becomes more challenging as the laser power increases. This study presents the successful implementation of a high-quality, high-intensity vortex laser beam exceeding 10²⁰W/cm²—an essential advancement for enhancing the performance and applicability of high-power lasers. We achieved this by integrating a spiral phase mirror (SPM) with an orbital angular momentum of l=1, specially designed for the vortex beam, along with an adaptive optical system, into a 150-TW femtosecond Ti:sapphire laser. Importantly, SPM, featuring a modulation structure to correct for a 45° incidence angle, was utilized to produce the vortex beam. The adaptive optical system, comprising a Shack–Hartmann wavefront sensor and a deformable mirror, employed a feedback loop to correct wavefront aberrations distorting the vortex beam. Notably, the negligible difference between the Hartmanngrams of the Gaussian and vortex beams (l=1) allowed the Gaussian beam’s Hartmanngram to serve effectively as the input reference for wavefront correction, resulting in a successfully corrected vortex beam wavefront. Experimental results, both pre- and post-wavefront correction, were compared with simulation results obtained via field-tracing. The peak intensity of the focused high-quality vortex laser beam ultimately reached 1.8×10²⁰W/cm², exceeding previously reported experimental results. The results of this study could significantly contribute to the exploration of high-intensity angular momentum transfer in relativistic laser-plasma interactions.

In this study, we introduce a novel real-time measurement and correction method for time-varying wavefront aberrations. Central to this method is a GPU-accelerated parallel algorithm based on phase diversity images. We apply an approximate model for the point spread function to reduce the computational load of error metric minimization. We forge a parallel framework that independently measures each aberration mode by deriving an object-independent error metric and its gradient. Numerical experiments with actual Kolmogorov model-based data were conducted to assess the measurement performance and real-time feasibility of the proposed method. When juxtaposed with the global optimization algorithm, the proposed method improved the computation speed by up to 1300 times, while maintaining measurement accuracy. Moreover, we executed benchmark tests on diverse hardware configurations, thereby verifying the real-time viability of GPU acceleration. The GPU achieved a 6.8x improvement in computational speed compared to the CPU. Seamlessly integrating a LQR controller into the adaptive optics system, we zeroed in on the real-time correction of dynamic aberrations. The empirical results exhibited an operational speed of 90 [Hz] in a realistic environment for correcting only three types of aberrations (astigmatism, defocus, and coma). Furthermore, we demonstrated the correction capability for large-scale aberrations, proving that the proposed method is scalable relative to the intensity of aberrations. In conclusion, this study paves the way for a combination of real-time execution and precise wavefront aberration correction in a sensorless AO, establishing a novel standard for future development and enhancements in wavefront sensing technology.

Spiral-phase-contrast imaging, which utilizes a spiral phase optical element, has proven to be effective in enhancing various aspects of imaging, such as edge contrast and shadow imaging. Typically, the implementation of spiral-phase-contrast imaging requires the formation of a Fourier plane through a 4f optical configuration in addition to an existing optical microscope. In this study, we present what we believe to be a novel single spiral-phase-objective, integrating a spiral phase plate, which can be easily and simply applied to a standard microscope, such as a conventional objective. Using a new hybrid design approach that combines ray-tracing and field-tracing simulations, we theoretically realized a well-defined and high-quality vortex beam through the spiral-phase-objective. The spiral-phase-objective was designed to have conditions that are practically manufacturable while providing predictable performance. To evaluate its capabilities, we utilized the designed spiral-phase-objective to investigate isotropic spiral phase contrast and anisotropic shadow imaging through field-tracing simulations, and explored the variation of edge contrast caused by changes in the thickness of the imaging object.

Spectrally encoded confocal microscopy (SECM) is a high-speed reflectance confocal microscopy technique. Here, we present a method to integrate optical coherence tomography (OCT) and SECM for complementary imaging by adding orthogonal scanning to the SECM configuration. The co-registration of SECM and OCT is automatic, as all system components are shared in the same order, eliminating the need for additional optical alignment. The proposed multimode imaging system is compact and cost-effective while providing the benefits of imaging aiming and guidance. Furthermore, speckle noise can be suppressed by averaging the speckles generated by shifting the spectral-encoded field in the direction of dispersion. Using a near infrared (NIR) card and a biological sample, we demonstrated the capability of the proposed system by showing SECM imaging at depths of interest guided by the OCT in real time and speckle noise reduction. Interfaced multimodal imaging of SECM and OCT was implemented at a speed of approximately 7 frames/s using fast-switching technology and GPU processing.

We propose a model predictive control (MPC) method to compensate for the time-varying phase aberrations in a sensorless adaptive optics (AO) system. The approximate model for the point spread function (PSF) of the imaging system with phase diversity is mathematically derived, and its validity is verified. The proposed MPC, which considers the operating limits of the deformable mirror (DM), computes the optimal applied voltage of each actuator over a prediction horizon, and the receding horizon scheme is applied as feedback control. Numerical case studies with the time-varying phase aberrations generated by an atmospheric turbulence simulator are presented to demonstrate the correction performance of the MPC strategy. The proposed method caused a 50% improvement in the reduction in residual aberration, making it competitive with a saturation linear quadratic regulator (LQR). The computational feasibility of the proposed method is validated using fast MPC, which approximates the primal barrier method.