This PDF file contains the front matter associated with SPIE Proceedings Volume 12975, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

In Free-Space Optical (FSO) communication, with the increase of bit resolution of M, the required bandwidth of PPM and DPIM increase sharply, and the bandwidth efficiency are extremely low. There is also a clock synchronization problem in the demodulation process of PPM and OOK. We propose a pulsed-laser Pulse-Number Modulation (PNM) method to address the high required bandwidth and low bandwidth efficiency for high-order modulation in FSO communication with traditional modulation methods. The symbol structure, power efficiency and bandwidth properties of PNM are presented. The modulation and demodulation of PNM are simple and easy to implement without complex clock synchronization processing. Additionally, we use the FPGA as the core controller to build an FSO communication system, which realizes accurate modulation and demodulation of data with PNM modulation method under the communication distance of 27 m and the bit rate of 2.5K bps.

MoSe₂ thin films have excellent catalytic, electrical, and optical properties and have potential applications in the fields of catalytic hydrogen precipitation, field effect transistors, sensor devices, and optoelectronic devices. In this paper, MoSe₂ thin films were synthesized based on the solid-phase reaction at the interface between Se and Mo film at high temperatures, which are deposited on sapphire substrates sequentially. The structure and morphology were characterized by Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The synthesis temperature and saturable absorption (SA) properties of the MoSe₂ films were investigated. The results show that 400°C is close to the optimal temperature for synthesizing MoSe₂ films, and the synthesized MoSe₂ films exhibit multilayer structure. When it is applied as a saturable absorber in a 1064 nm solid-state laser, the maximum repetition frequency of the Q-modulated laser pulse is obtained to be 428.1kHz, which corresponds to a pulse width of 67.6 ns and a maximum modulation depth of 27.4%.

With the improvement of the level of social and economic development and the improvement of living standards, the amount of garbage output in China is increasing year by year, and the problem of garbage disposal is becoming more and more serious. In view of this situation, China began to carry out garbage classification. Garbage classification can give full play to the utilization value of resources and means of production and reduce the impact of human economic activities on nature. Therefore, aiming at the problems of difficult garbage classification and low efficiency of manual sorting, this paper designed and developed an intelligent garbage sorting vehicle. The system combines the background replacement algorithm to enhance the garbage data set, detects and classifies the garbage targets through the improved YOLOv5 network model, and finally realizes the garbage sorting work through the all-terrain intelligent vehicle equipped with mechanical arm. Through the test of garbage sorting in the real environment, the success rate of garbage identification by the intelligent garbage truck is 85%, which can meet the needs of garbage sorting in real life.

Spatial heterodyne spectral technology is a hyperspectral remote sensing technique. With the improvement in detection accuracy, new demands have emerged for denoising methods in spatial heterodyne interferograms. Convolutional neural networks (CNNs) is a currently hot research topic. they have unique advantages in extracting abstract features from data. In recent years, CNNs have demonstrated outstanding performance in the field of image denoising. In this paper, we construct a Spatial heterodyne interferograms denoise CNN(SHI-DnCNN) using batch normalization and residual learning. We utilize the trained SHI-DnCNN to denoise spatial heterodyne interferograms contaminated with Gaussian noise. The results show that SHI-DnCNN exhibits excellent Gaussian noise denoising capability for spatial heterodyne interferograms. Furthermore, we evaluate the denoising results using PSNR, SSIM, and residual spectra, further confirming the superior denoising performance of SHI-DnCNN. This work provides a new and effective solution for denoising spatial heterodyne interferograms.

Simulations of terahertz signals in the time or frequency domain focus on the photoconductive antenna (PCA). However, they lack a simpler and more accurate simulation technology for PCA, which plays a crucial role in designing and optimizing detectors. Such work is essential in terahertz imaging and time-domain spectroscopy (THz-TDS). This work simulates an incident terahertz wave by introducing a three-dimensional (3-D) finite-difference time-domain (FDTD) simulation in the form of a total field to scattering field. This wave is pretreated as a plane wave that is incident on the receiver. The equation of carrier dynamics with semiconductor charge and transport is solved by using the 3-D full-wave FDTD method. A center surface current method is used to calculate the time-varying conductivity. A sampling electric field was used to evaluate the photocurrent. They were obtained by convolving the main time-varying photoconductivity of the photoexcited carrier distribution on the cross-section in the middle of the gap of a PCA receiver. Then, we compare these simulations with previously reported data from an incident terahertz signal. In addition, we simulated the detection characteristics with other results in the literature. Our simulation tool can accurately reproduce these data sets. These simulations can be used to design and optimize the receiving performance of different PCAs structures before costly fabrication has commenced.

Silicon modulators play an important role in silicon photonics for efficient modulation and transmission of optical signals. Enhancing the performance of silicon modulators has largely relied on optimizing doping profiles. However, in recent years, progress in finding superior solutions to optimize performance has faced obstacles. To address this challenge, the concept of inverse design, which has gained popularity in passive photonic devices, can be applied to silicon active devices by dividing the doping region into segments and adjusting each segment based on feedback from the results. Consequently, we introduce the inverse design method into modulator doping profile optimization by utilizing the particle swarm optimization (PSO) algorithm, resulting in the attainment of a G-shaped doping profile for the modulator. The proposed modulator demonstrates the superior V_πL of 0.48 V·cm and the low loss of 13.5 dB/cm. The small-signal frequency response suggests a reliable operation range under reverse biases of 1 V to approximately 3 V with the bandwidth over 26 GHz. The G-shaped silicon modulator exhibits impressive modulation efficiency and minimal loss, indicating its high potential for use in microwave front-end applications. The utilization of inverse design holds immense promise in advancing active silicon photonic devices for faster, higher-capacity and more reliable data communication systems.

Limited statistical frame number and strong backscatter interference from smoke result in a photon-starved regime, severely limiting the depth imaging capability of array Gm-APD lidar in smoky environment. Here, we propose a depth image estimation algorithm that can significantly improve the integrity of targets in dense smoke environments when signal photons are starved. At the signal level, the algorithm improves the accuracy of extracting signal photons by constructing multi-scale superpixels. At the image level, using edge information of depth images at different scales to guide and fill the original scale depth image achieves efficient noise reduction and improves target integrity. It has been successfully demonstrated under different attenuation lengths and statistical frame numbers. Compared with other state-of-the-art methods, the proposed algorithm has maximum target recovery and structural similarity, especially for the attenuation length (AL) is 3.6 and statistical frame number is 1500 (imaging time is 75ms). This study is of great significance for the fast depth imaging of dynamic targets by array Gm-APD lidar in dense smoke environments.

The Stochastic Parallel Gradient Descent (SPGD) algorithm is a widely used model-free optimization algorithm in adaptive optical systems. However, when affected by noise, the SPGD algorithm may incorrectly estimate the gradient, resulting in a significant decrease in its performance and limitations in its application in complex environments. To address this issue, this paper introduces the optimal estimation algorithm and adds a self-checking process to the SPGD algorithm, proposing a Kal-SPGD algorithm. The feasibility of the Kal-SPGD algorithm is verified through simulation and experimentation. The experimental results show that compared with the standard SPGD, the use of the Kal-SPGD algorithm can reduce the signal amplitude variance by up to 92.15%. The Kal-SPGD algorithm provides a more favorable control technique for adaptive optical systems.

We propose a hybrid structure nested anti-resonant nodeless hollow-core fiber (HS-NANF) that possesses ultra-low Confinement Loss (CL) and excellent single-mode characteristics. By optimizing all key parameters through data analysis, we have achieved a CL of less than 0.01 dB/km in the 920 nm to 1600 nm wavelength range, and the minimum value of CL is 0.00063dB/km at 1550 nm. Additionally, the loss ratio of high-order modes to fundamental modes (HOMER) in the 800nm wide band of HS-NANF is much greater than 1000, and the HOMER is 11609 at 1550 nm, reaching a maximum value of 177276 at 920 nm. This means that HS-NANF can ensure excellent single-mode transmission in the ultra-wide band. In addition, HS-NANF also has good bending characteristics. When the bending radius is 6 cm, the loss introduced by bending is close to 0.01 dB/km, and when the bending radius is greater than 10 cm, the loss introduced by bending can be ignored. These excellent characteristics make HS-NANF an ideal transmission medium for low-latency broadband communication systems that rely on hollow-core fiber technology.

The development of optical communication makes CWDM technology unable to meet the design requirements, and the cost of 100GHz filter, a key optical device in DWDM technology, is high and the scale application is limited. In order to reduce the preparation cost of 100GHz filter and promote the development of DWDM technology, this study adopts high-power medium-frequency pulse magnetron sputtering technology for preparation, studies the sputtering power and analyzes the influence of oxygen and argon supply on sputtering of different sputtering materials. The thickness uniformity of the films is not less than 0.04%, and the sputtering rate is greater than 0.4nm/s. The design result is imported into the coating machine for automatic preparation. The insertion loss of the prepared product within the radius of 40mm is 0.1dB, the thickness difference of the film is less than 0.05%, and the preparation time is less than 30 hours. Finally, more than 2500 pieces of the finished filter can be obtained, and the output has been significantly improved, reaching the world's leading level.

Lock-in amplifier (LIA) plays a crucial role in the field of photoacoustic trace gas detection. In this paper, we introduce an innovative concept termed the virtual digital Lock-in Amplifier (VDLIA) using matched filtering techniques. The VDLIA exhibits exceptional proficiency in accurately determining both the amplitude and phase of sinusoidal signals, even in the presence of heightened levels of noise. Pivotal factors influencing the VDLIA’s performance, including the characteristics of the low-pass filter, and the resolution of the analog-to-digital converter (ADC), were examined under diverse noise conditions. To evaluate the effectiveness of the VDLIA, it was integrated into a photoacoustic system designed for the detection of SO₂ concentration. Experimental results demonstrate that the output results of the proposed VDLIA closely align with those generated by a commercial LIA, offering significant potential for various industrial applications.

The present study reports the performance of a Dy³⁺, Tb³⁺:LiLuF₄ yellow laser at 574 nm that could be efficiently operated in both continuous-wave (cw) and passive Q-switching modes. Using two blue InGaN-laser diodes as the pump source, a cw yellow laser was generated with an output power of 315 mW at the wavelength of 574 nm. The passively Q-switched pulse laser was obtained using Bi₂Se₃ and Bi₂Te₃ as saturable absorbers. The saturable absorbers prepared by the chemical vapor deposition method were characterized by Raman spectroscopy and atomic force microscope. The modulation depth and saturable intensity of saturable absorbers were explored by an irradiance-scan technique in a nanosecond regime. With 3.18 W of pump power absorbed, a pulsed output power of 45 mW was generated at 66.7 kHz of repetition frequency, with a minimum pulse width of 735 ns using Bi₂Se₃ as a saturable absorber. In the case of the Bi₂Te₃ saturable absorber, the shortest pulse duration of 828 ns is achieved at the pulse repetition frequency of 22.3 kHz, corresponding to the pulsed output power of 38 mW. The outcomes of the study suggest that Bi2Se3 and Bi2Te3 are potential nanomaterials for optoelectronic applications in the yellow regime.

Line shapes observed in attosecond transient absorption spectra (ATAS) encode information on the phase of the optical dipole response. Understanding and controlling the phase evolution of interference fringes is among the fundamental goals of exploring coherent interaction. Here, we simulate the attosecond transient absorption in the near-infrared (NIR) dressing field by considering a three-level model in the adiabatic approximation. We find that the absorption line shape can be changed from Lorentzian to Fano to inverted Lorentzian and back again at two-photon dressed energy levels “ω ± 2ω_ι”, and line shapes evolve in half-cycle periodicity (T/2). Moreover, the direction of phase evolution of “ω ± 2ω_ι” is opposite, while the phases of “ω ± 2ω_ι” are roughly the same at certain delays with an interval of approximately a quarter-cycle periodicity (T/4). These results demonstrate that absorbance of two-photon dressed energy levels “ω ± 2ω_ι” can qualitatively map the AC Stark shift. These observations provide new insights into the control of spectral line shapes and open the way for the modulation of quantum optical interference in the laser-driven atom.

Ultraviolet photoacoustic imaging can detect the ultrasonic signals released by the cell nucleus through the strong absorption of ultraviolet light by DNA and RNA in organisms, which thus obtains images similar to those from traditional hematoxylin-eosin staining but no need of staining or sectioning. However, the traditional Optical-Resolution Photoacoustic Microscopy (OR-PAM) working in the ultraviolet band only maintains a micrometer-scale lateral resolution in a very limited depth range. Due to short Depth of Focus (DOF), the resolving capability of photoacoustic imaging deteriorates sharply, resulting in a severe degradation of image quality and adversely affecting the reliability of histopathologic diagnosis. Based on an extended Nijboer-Zernike (ENZ) theory of optical field regulation, a millimeter-level phase plate modulator of liquid crystal is designed to engineer the wavefront of ultraviolet photoacoustic illumination, achieving an increase in the DOF of the OR-PAM system at ~210 μm while maintaining a good lateral resolution of ~1.04 μm. This surpasses the traditional OR-PAM with Gaussian-mode excitation laser. The liquid crystal modulation is potentially valuable for obtaining non-destructive and label-free histology photoacoustic images of the cell nucleus.

Photoacoustic measurement technologies have demonstrated great potentials for studying physiological and pathological processes within biological tissues, including blood flow, cellular metabolism, physiochemical signature and oxygen metabolism. However, the limited bandwidth of piezoelectric transducers fails to respond broadband ultrasonic signals of complex biological particles in the conventional photoacoustic measurement systems, which possibly overlooks abundant information encoded in the frequency domain of the ultrasonic waves. By exploiting the ultrafast temporal dynamics and strongly confined evanescent field of optical surface wave, we take advantage of a high Numerical Aperture (NA) objective to develop a series of broadband and high sensitivity ultrasonic sensing technologies of optical evanescent waves. For example, Surface Plasmon Resonance (SPR) sensors could measure pressure transients caused by ultrasonically modulated light reflectivity, demonstrating a high sensitivity of approximately 675 Pa and broad bandwidth of approximately 108 MHz. By constructing a sensing layer of the multilayer film based on composite waveguide, we developed multi-layer film waveguide photoacoustic detector (MWPAD) and further improved the sensitivity (approximately 208 Pa) and bandwidth (approximately 123 MHz). Further, we have exploited extremely sensitive phase shift evanescent wave sensor to convert the ultrasonically modulated phase shift into the light interference intensity, achieving detection sensitivity at approximately 174 Pa over a broad bandwidth of approximately144 MHz. We believe that our proposed sensing technologies of optical evanescent waves potentially promote biomedical ultrasonic/photoacoustic applications.

Atmospheric delay induced by refraction is a significant factor influencing the accuracy of Satellite Laser Ranging (SLR). While ray tracing technique is recognized for its precision in estimating atmospheric delay, there's a gap in the research concerning the computation of integration step size and its impact on results. Therefore, various calculation methods for integration step size were compared and ray tracing with different step sizes were employed to calculate atmospheric delay at Zhuhai Tianqin Station (referred to as "TQ station"). Under different elevation angles, a comparative analysis was conducted to assess the differences in the results and these results were further compared with those from the Mendes-Pavlis model and VMF3o model. The exploration of the relationship between the calculation errors and meteorological factors as well as integration step size indicate that it is essential to select an appropriate integration step size and parameter combination before conducting ray tracing. To achieve millimeter-level accuracy in results, the initial integration step size should be below 50 m. Nevertheless, to avoid data errors, excessively small initial integration step sizes should be avoided. This study highlights the importance of choosing an optimal integration step size and provides valuable insights for improving the precision of atmospheric delay estimation in SLR.

Silicon nitride (SiN) is an ideal material which is compatible with complementary metal-oxide-semiconductor (CMOS) technology. Its advantages include suitability for a large spectral range, low propagation loss and low thermo-optic coefficient, etc. Wavelength division (de)multiplexing (WDM) device is a crucial component for optical transmission networks. In this paper, we demonstrate a six-channel WDM device built with angled multimode interferometer (AMMI) structure in SiN material. Using the first- and second-order self-imaging effects in the multimode waveguides, the number of the multiplexed channels is increased from 3 to 6, without increasing the overall length of the device. The device is designed to operate in the C+L band, and the central wavelength spacing between the neighboring channels is 20nm. The simulation results show that the insertion loss of the device in each channel is less than 0.81dB and the averaged crosstalk of the channels is ~14.9dB. Meanwhile, the device also exhibits low temperature sensitivity and large fabrication tolerance, which is suitable for mass production in commercial foundries.

Controlled nuclear fusion through laser Inertial Confinement Fusion (ICF) is currently being developed. It is of great significance for energy security, high energy physics and national defense, etc. High-precision x-ray microscopic imaging techniques have become the key to revealing material phenomena and laws under extreme conditions. This paper proposes an open-type Wolter microscope configuration. By utilizing the configuration, a number of modern polishing techniques can be utilized and a balance between imaging performance and the feasibility of optical processing can be achieved. The original enclosed and inner Wolter mirror surfaces have been changed to unclosed outer surfaces. The configuration is characterized by high spatial resolution, large depth of field, and high throughput, among other features. And these characteristics are urgently needed in high-precision x-ray imaging diagnostics. The technical scheme and optical considerations of the configuration are detailed. Ray tracing simulation is used to design key optical parameters and evaluate system imaging performance. In addition, this configuration has potential for various diagnostic purposes, including sub-micron spatial resolution imaging, high-energy high-throughput imaging, multi-color and multi-channel imaging, and more.

We demonstrate a dual-wavelength pulsed mid-infrared (MIR) optical parametric oscillator (OPO) with flexible temporalspectral operation capability. The OPO was pumped with a fiber master-oscillator power-amplifier (MOPA) incorporating an acousto-optic tunable filter (AOTF) in the seed oscillator. Composite wave packets were generated to drive the AOTF with adjustable carrier frequencies, amplitudes, packet lengths, and inter-packet periods, enabling flexible temporalspectral manipulation of the seed laser in central wavelengths, spectral intensities, pulse profiles, and repetition rates, respectively. This versatile laser was employed to pump the OPO after power amplification and the temporal-spectral characteristics were transferred to the MIR in the nonlinear processes. Two typical pulsed dual-wavelength operation modes, namely, simultaneous and alternate dual-wavelength pulsation modes, were experimentally studied for the pump MOPA and the related OPO. Equivalent spectral intensities were obtained for the two MIR idler wavelengths under both operation modes with careful drive signal adjustment for the AOTF. It is believed that our design has paved a promising approach towards the construction of versatile pulsed MIR sources with flexible temporal-spectral operation modes, serving practical applications such as differential absorption lidar and terahertz wave generation.

Atomic clocks are precise devices that generate time and frequency signals by exploiting the inherent oscillation frequency of atoms. They have broad applications in fields such as aerospace navigation, global positioning, and precision metrology. Laser frequency stabilization techniques are crucial for ensuring the stable operation of atomic clocks, laser frequency stability directly impacts the performance of these clocks. This review presents the working principles, characteristics, and research progress of different laser frequency stabilization techniques, including saturation absorption spectroscopy stabilization, Pound-Drever-Hall technique, and modulation transfer spectroscopy stabilization. Additionally, it provides a perspective on the future advancement of laser frequency stabilization techniques in the atomic clock filed, which integral in the development of high-performance atomic clocks.

Infrared imaging systems have many advantages, such as full-time employment, good concealment, high resolution, strong anti-interference ability, so they have become the military and civilian focus so far. In this paper, we explored to construct the evaluation system about detection performance of infrared imaging systems based on infrared physics theory and the action mechanism between infrared radiation and detector. First of all, infrared detection mechanism of point target has been investigated under long distance condition. We derived the solving formula of detection range and proposed the method of calculating the mutual position of target and detection system to reduce false alarm rate. Secondly, we constructed the evaluation system on detection performance of area target, and mainly combined the area distribution of target imaging on the photodetector, signal to noise ratio of target, the contrast between target and background. The detection range of area target was the minimum value of the three factors. The simulation results indicated that the constructed evaluation system of point target and area target can fully evaluate detection performance of infrared imaging systems.

We propose a switchable photonic nanojet (PNJ) generated by a truncated cylindrical structure covered with a thin film of vanadium oxide (VO₂). The switching of the PNJ is realized by the change of external temperature. By changing the temperature, the properties of the VO₂ film can be changed to achieve the switching between metallic and nonmetallic phases, which in turn switches the PNJ. In addition to this, we optimized the dimensions of the truncated top cylinder and the thickness of the film, which led to a further improvement of the properties of the PNJ. The results show that the structure works with a strength contrast of 85.62% between the open and closed states of the PNJ. Overall, this structure adds the parameter of temperature to the modulation of the properties of the PNJ, which is of great significance for the development of novel integrated photonic devices.

In this paper，the liquid-based scattering microspheres phantom is studied, in order to evaluate the resolution of optical coherence tomography (OCT) equipment. By mixing pure water and polystyrene (PS) microspheres in proportion to fabricate solutions of different concentrations. The disadvantages of polydimethylsiloxane (PDMS) substrates are overcame, such as complex production process, microbubbles, uneven distribution or clustering of microspheres, easy tearing, and relatively low imaging contrast. The encapsulated liquid-based scattering microspheres phantom is characterized by optical microscopy, which shows that the microspheres are uniformly distributed without clustering. It can effectively improve the accuracy of resolution evaluation of OCT equipment. At the same time, the automatic identification, averaging and fitting of microspheres in OCT test images are realized by programming, and the evaluation results of lateral and axial resolutions are given automatically. Finally, the liquid-based evaluation phantom is validated by testing the resolutions of a commercial OCT equipment.

To solve the problem that the type and area of macular disease are not easy to identify due to the irregular scale and unobvious characteristics of macular disease region on retinal OCT images, an improved YOLOv8n macular disease detection model is proposed, and a data set of retinal macular disease detection is established. Firstly, the feature pyramid module of bidirectional weighted feature fusion was added. Secondly, the attention mechanism was introduced. Finally, the novel loss function was replaced. The improved model can complete the multi-scale and irregular multi-objective training task of retinal maculopathy. The experimental results show that the improved model has a good effect on the self-built data set. The accuracy of central serous macular degeneration, macular hole, and choroidal neovasculation can reach 97.7%, 97.8%, and 97.4%, respectively, and can accurately identify the location of the lesion.

To study the physical mechanism of atomic Rydberg state excitation (RSE) in two-color laser fields, we solve the time-dependent Schrödinger equation (TDSE) to calculate the ionization and excitation of hydrogen atoms. The relationship between the excited state population and the excitation rate of hydrogen atoms and the intensity of the fundamental frequency (FW) field can be observed by adjusting the laser intensity of the second harmonic (SH) field. The results demonstrate that multiphoton resonance absorption aligns with the physical mechanism of atomic resonant state excitation in two-color laser fields.

Lensless diffuser camera is a novel and flexible approach to capture object’s images. Here, we propose a compact spectral and polarization diffuser camera (SPDC) enabled by a diffuser and a complementary metal oxide semiconductor (COMS) sensor. We demonstrated SPDC to reconstruct images with spectral and polarization by simulations. It can be highly integrated with lightweight, and lower cost, compared with traditional multi-dimensional imaging systems. SPDC has great potential in many applications, such as compact bioimaging systems, portable optical sensing, and consumer applications.

Super-resolution microscopy provides a high spatial resolution that is beyond the diffraction barrier and can visualize nano-sized structures and interactions in biological and material study. In recent years, lanthanide-doped upconversion nanoparticles (UCNPs) that can upconvert the near-infrared (NIR) excitation photons to visible emission photons, have been developing as a kind of novel nanoprobes for bioimaging. Here we report the recently developed NIR superresolution imaging techniques by exploring the nonlinear fluorescence responses in UCNPs. Upconversion Nonlinear Structured Illumination Microscopy (U-NSIM) employes nonlinear fluorescence, along with NIR excitation and emission light, to deliver rapid frame rates and high-resolution capabilities, enabling in-depth super-resolution imaging. The tunability of lifetime in UCNPs is also introduced to develop the multiplexed super-resolution imaging with lifetime-engineered nanoprobes. By detecting two emission channels with different nonlinear fluorescence responses, a single doughnut illumination beam is used to scan the sample to generate a Gaussian-like emission point spread function (PSF) and a doughnut-emission PSF simultaneously, which can be fused by algorithms to an optimized super-resolution nanoscopy. These upconversion super-resolution imaging techniques provide new strategies to develop deep-tissue and multiplexed super-resolution imaging and also help to achieve it in a simple optical scheme.

Germanene (Ge) has a Dirac-type electronic structure similar to that of graphene and has excellent nonlinear saturable absorption properties, which has attracted extensive research. In this paper, few-layer Ge nanosheets were prepared and characterized in detail. Its nonlinear modulation depth was measured to be 8.5%, and the saturation intensity was 0.12 GW/cm2. Ge nanosheets are used as a saturable absorber (SA) in an Er-doped fiber laser (EDFL) to obtain a stable Q-switched mode-locking (QML) pulse. As the pump power (Ppump) increases from 64.2 mW to 204 mW, the repetition frequency (RF) and pulse width of the Q-switched (QS) envelope increase from 46.2 KHz to 109 KHz and decrease from 4.4 μs to 2.25 μs, respectively. The mode-locked pulse has a RF of 30.2 MHz with a center wavelength of 1559.6 nm. The QML pulses obtain a maximum output power of 2.278 mW and a maximum pulse energy of 20.9 nJ when the Ppump is 204 mW. Our study proves that Ge, as a high-energy light pulse absorbing material, can be used in the field of ultrafast laser.

Miniature spectrometers are in high demand for portable optical sensing, on-chip systems, and other consumer applications, due to their small size and light weight. Recently, on-chip spectrometers, which are based on simple hardware systems, and recover unknown spectra by reconstruction algorithms, have become one of the most important research trends. Such on-chip computational spectrometers typically employ random spectral filters such as quantum dot arrays, photonic crystal arrays, and so on. However, these random spectral filters generally need expensive materials or complex preparation processes. So, the low-cost and easy-to-prepare spectral filters are pursued in developing computational spectrometers. Here we report the on-chip spectrometer using polarization-responsive filters, which are directly placed on top of a CMOS sensor. These spectral filters contain birefringent material and two polarizers and generate different transmittance spectra by the complex optical interference of them with different polarization angles. We verified the validity of this approach by simulation. This spectrometer only uses polarizers, micas, and a CMOS sensor, and has the advantages of low cost, simple preparation, and small footprint.

We study here the high-order harmonic generation (HHG) from the hydrogen molecular ion H₂⁺ aligned along the axis of a golden nanotip. The whole system is shined by a chirped laser pulse with its wavelength centered at 800nm. Due to the existence of the metallic nanotip, the light field experienced by the molecular ion is strongly enhanced owing to the generation of the local surface plasmon field. It is found that the cutoff position and the conversion efficiency of HHG depend strongly on the distance between the nanotip and the molecular ion, as well as on the chirp parameter of the input infrared laser field. The plateau of the HHG is largely extended with negative chirps, and the supercontinuum spectra that can support a single attosecond pulse are generated by the suppression of the long electron trajectory with an optimized field chirp parameter.

In recent years, the dark hollow beam is a kind of special beam, which is characterized by zero light intensity in the center of the propagation direction and high light intensity around. A J₀-correlated Schell-model beam is one of the representative of the dark hollow beams. In view of this, according to the expression of light intensity of dark hollow beam in turbulent biological tissues, combining Fourier transform and convolution definition, on the basis of the analytical expressions of the propagation factor of a J₀-correlated Schell-model in turbulent biological tissues, this paper discovered that: compared with the free space, the parameters of turbulent biological tissue have certain effects on the propagation factor of a J₀-correlated Schell-model beam with the propagation distance changing. In practical application, it is of great significance to control propagation characteristics and quality of the J₀-correlated Schell-model beams in turbulent biological tissues.

An external cavity wavelength-locked red semiconductor laser with a narrow-linewidth was designed and fabricated. The AlGaInP strained quantum wells were meticulously designed and grown,while the epitaxial layer of a high-power red semiconductor laser was synthesized using metal-organic chemical vapor deposition (MOCVD).The chips were fabricated by photolithography, metal electrode fabrication, cavity surface coating and other processes. The prepared laser chip with the cavity length of 1.5 mm has a strip width of 100 μm. The chip was made into a laser device through packaging technique, and an external resonant cavity was constructed using a Volume Bragg Grating. A series of oexperiments were conducted to optimize the performance of laser devices, and the characteristics of spectrum, power and other parameters in the condition of free running spectrum and wavelength-locked spectrum at different temperatures. A narrow-linewidth red semiconductor laser with the central wavelength of 640 nm, the linewidth of 0.11 nm, and the power of 2.7 W was obtained by means of the continuous drive current measurement at room temperature with the drive current of 3 A and fiber parameters of 50/125. In addition, the output power of 5.02 W was achieved with the method of the quasi-continuous drive current of 5 A.The power loss of the external cavity mode-locked using VBG is controlled within 3%.

In recent years, arrayed atomic magnetometers have been continuously applied in biomagnetic scenarios. However, the crosstalk between adjacent sensors introduced by the modulated magnetic fields significantly compromises the imaging accuracy of arrayed atomic magnetometers. To solve this problem, a detuned square-wave optical modulation zero-field atomic magnetometer configuration is developed and we provide an analytical solution of this method. In this scheme, the circularly polarized pump light is used to polarize alkali metal atoms longitudinally, and a beam of detuned square-wave modulated circularly polarized light is applied transversely to generate a light-shift modulation instead of the coil-generated modulated magnetic field. Then the transverse magnetic field is measured by the optical absorption method of longitudinally circularly polarized pump light. This scheme maintains the inherent advantage of high sensitivity in spinexchange relaxation-free (SERF) atomic magnetometers. Additionally, the all-optical configuration eliminates the need for additional modulated magnetic fields or radio frequency (RF) fields, thereby mitigating crosstalk issues associated with modulated magnetic fields in array applications. Consequently, this scheme exhibits great potential for arraying and is expected to be employed in magnetocardiography (MCG) and magnetoencephalography (MEG).

Vascular-targeted photodynamic therapy (V-PDT) has become an important therapeutic method for blood vessel-related diseases such as Port-Wine Stains (PWSs). To achieve more precise V-PDT, quantitative evaluation of V-PDT efficiency appears to be an essential prerequisite. In previous study, methods of Euclidean distance and two-dimensional correlation coefficient, which were calculated based on PWS lesion images, had been employed to evaluate the efficacy of V-PDT. However, results of the mentioned methods show little difference for different V-PDT efficiency, which indicates a limited sensitivity leading to difficulties in V-PDT efficacy evaluation. In this work, evaluation methods with higher sensitivity, including pixel count change, average gray value change, and entropy change which were analyzed based on lesion images before and after V-PDT, were developed for V-PDT efficiency evaluation on PWS. These evaluation methods reveal V-PDT effect from aspects of lesion area, skin color, and skin texture. In addition, relative difference rates of all methods were analyzed for sensitivity comparison. The results indicate that changes of pixel number, average grayscale value, and entropy well reflect differences in V-PDT efficacy and exhibit much higher sensitivity in comparison with that of Euclidean distance and two-dimensional correlation coefficient, confirming themselves a promising quantitative evaluation method for V-PDT efficacy.