Correlative imaging of soft X-ray tomography (SXT) and fluorescence microscopy (FM) has emerged as a promising strategy to provide complementary morphological and functional information. Despite much progress achieved in correlative imaging, precise identification of three-dimensional subcellular structures inside cells needs to be improved. Here, we present a high-resolution correlative imaging method by coupling ground state depletion microscopy followed by individual molecule return (GSDIM) and Cryo-soft X-ray tomography (Cryo-SXT). The custom-designed correlative imaging enables to provide high spatial resolution fusion image of three-dimensional subcellular structure inside cell with depth of several micrometers. Furthermore, the GSDIM is facile, cost-effective and maneuverable. We believe this advanced technique would be a powerful imaging toolkit to provide useful and comprehensive information in bioscience.

Quantum digital signature (QDS) has been proved to be secure in theory, but will inevitably be interfered by channel noise during the practice transmission of qubits. We propose two practical fault tolerant quantum digital signature protocols for the collective noises. For resisting the collective noises, a decoherence-free subspace (DFS) containing four logical qubits has been constructed, which improves the performance of QDS protocols in terms of communication fidelity. Moreover, we prove that the protocols are secure against forging and repudiation attacks, and further discuss the influence of different verification thresholds on the security and give a quantitative analysis.

Spatially and spectrally resolved imaging (S2 imaging) is a technique that was developed as an alternative to beam quality (M2) measurements to characterize the modal content of large mode area (LMA) fibers. While it is known that the success of S2 imaging is highly dependent on the broadband source and the launch conditions into the fiber, the information resulting from this method is more limited than may appear at first glance. Experiments and numerical simulations are used to show that (a) the accuracy of the reconstructed LP01 mode profile varies greatly depending on launch conditions, and (b) there are always errors in the reconstructed LP11 mode profile. Not only do these findings reveal that the reconstructed mode areas cannot be accurately determined, but it also shows that the relative modal intensities can only be determined accurately under nearly perfect conditions of fundamental mode launch and propagation through the fiber. Despite these findings, the S2 technique can still be used under nearly ideal launch and propagation conditions to identify the modes and their group delays, and accurately reconstruct only the fundamental mode.

Photonically tailored thermal emission can boost the efficiency of thermophotovoltaics through selective emission of above-bandgap energies. 1D photonic crystals are attractive candidates for this purpose, providing strong modulation of the optical density of states at the photonic band edge. However, optimization of the emission spectrum of such multilayer structures is challenging due to the large number of parameters involved. Here, we present the inverse design of an Al2O3/W multilayer using an evolutionary optimization algorithm. The experimental realization of the optimized design shows emission close to unity at above-bandgap energies while suppressing up to 40% of below-bandgap energies.

In this work, we demonstrate the generation of breather solitons in an aluminum nitride (AlN) microresonator. Our study shows different techniques for excitation of breather solitons together with stimulated Raman scattering (SRS) by pumping the fundamental transverse electric (TE00) mode. With suitable pump power and laser scan speed, we can eliminate the Raman effect and achieve a single soliton comb (FSR ∼ 374 GHz) beyond 4/5 of an octave-spanning bandwidth (1200–2100 nm). We have also demonstrated the breather and single soliton (FSR ∼ 364 GHz) states by pumping the first-order TE (TE10) mode using another device with a similar geometry. Our study adds significant development in the dynamics of solitons in the AlN platform.

Pulse compression by second harmonic generation in a type II nonlinear optical crystal controlled by a time predelay of the faster input pulse is not simple to achieve high-average-power Yb:YAG lasers with wavelength of 1030 nm. The reason is that the borate nonlinear crystals with their excellent thermal properties do not have the optimal ratio of group velocities of the interacting pulses to achieve efficient pulse compression. We have changed the effective group velocities by tilting the pulse fronts at a diffraction grating and imaging the tilted 1.7 ps pulses into the 6 and 8.5 mm thick BBO crystals. As a result, we have measured significant spectral broadening to 4.5 nm, supporting pulses as short as 100 fs, with an energy conversion efficiency in excess of 20 %. The measured data correspond well with numerical simulations. This research opens a way to extend the range of possible applications of Yb:YAG high-average-power thin-disk lasers into the fs regime.

The demand for terahertz (THz) sources that can be used in practical implementations has not yet been fully met. Through the development of small-scale free-electron lasers (FEL), we investigated a solution to overcome the low lasing gain of the FEL, which is caused by a small-current accelerator and a short-length undulator. To enhance the FEL gain, the FEL interaction between the electron beam and radiation was increased by reducing the cross-sectional area of the FEL oscillator mode. We developed a waveguide for the FEL oscillator, which has a remarkably small eye-shaped cross section with low wave loss. The mode cross-sectional area was calculated to be just 4 mm2 (full width at half maximum), which is considerably smaller than those of the free-space Gaussian mode and other waveguide modes. Using COMSOL Multiphysics simulation code, we calculated and analyzed the attenuation loss and mode cross-section area for waveguides of different shapes and sizes, and we observed that the dielectric coated eye-shaped waveguide has the lowest attenuation loss, that is, less than 2.5% for 1-m propagation at an operating wavelength of 300–600 µm. These results are in good agreement with our requirements for the tabletop THz FEL. Finally, we showed that the calculated operating wavelength range of the waveguide-mode THz FEL is 300–600 µm using the machine parameters of an accelerator and undulator that were developed by considering the dispersion relations of the eye-shaped waveguide and undulator radiation.

Terahertz imaging is an emerging candidate to diagnose breast cancers in a label-free manner. However, detailed terahertz analysis of early stage breast cancers is difficult to achieve owing to its low spatial resolution. In this study, utilizing a probe-less terahertz near-field microscope named scanning point terahertz source microscope, we visualize an unstained comedo ductal-carcinoma-in-situ including an architectural structure (comedo necrosis) measuring ∼ϕ500 µm, which is known as highly-malignant early-stage breast cancer, in terahertz images for the first time. The outcome is a critical step toward the label-free diagnosis of single early stage cancer lesions with terahertz waves.

The utilization of directional couplers (DCs) as power splitters and combiners is ubiquitous for the realization of integrated silicon photonic devices in the silicon-on-insulator (SOI) platform. Benefiting from the excellent modal modulation performance of graphene in silicon waveguides, we present its high flexibility to engineer and reduce the wavelength dependence of devices based on the DC. In this regard, a wavelength-insensitive 3-dB optical power coupler (3-dB OPC) is firstly proposed, in which various power splitting ratios are realized for the TE mode. Next, we design a broadband polarization beam splitter (PBS) consisting of a silicon waveguide (SW) and a graphene-silicon vertical slot waveguide (GSVSW). The simulation results show that the proposed PBS has high polarization extinction ratios (PERs) of 20.93 and 20.4 dB and low insertion losses (ILs) of 0.12 and 0.21 dB at 1550 nm for the thru and cross ports, respectively. In addition, the designed PBS demonstrates the ability to work over a wide range of wavelengths by changing the chemical potential of graphene.