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The image on the cover for Chinese Optics Letters Volume 19, Issue 11, summarizes the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective, some insight into the future of PAI technology in clinical applications is also provided.The image is based on original research by Dengfeng Li et al. presented in their paper "Review of photoacoustic imaging for microrobots tracking in vivo [Invited]", Chinese Optics Letters 19 (11), 111701 (2021).

The image on the cover for Photonics Research Volume 9, Issue 11, proposes a device that could be used for both display and visible light communication (VLC) applications. The semipolar blue &mu;LED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. The image is based on original research by Tingzhu Wu et al. presented in their paper "Highly stable full-color display device with VLC application potential using semipolar &mu;LEDs and all-inorganic encapsulated perovskite nanocrystal", Photonics Research 9 (11), 11002132 (2021).

The image on the cover for Advanced Photonics Volume 3 Issue 5 depicts a novel spintronic-metasurface terahertz emitter, developed by researchers from Fudan University. Composed of alternating magnetic heterostructures, the emitter allows efficient, flexible generation and manipulation of chiral terahertz waves. Terahertz radiation is generated by exciting the emitter with laser pulses under an oriented external magnetic field. Transverse anisotropic confinement of the laser-induced charge currents imposed by the metasurface structure leads to chiralterahertz-wave emission.The image is based on original research presented in the report by Changqin Liu, Shunjia Wang, Sheng Zhang, and Qingnan Cai, et al., “Active spintronic-metasurface terahertz emitters with tunable chirality,” Adv. Photonics 3(5), 056002 (2021), doi: 10.1117/1.AP.3.5.056002.

The image on the cover of High Power Laser Science and Engineering Volume 9, Issue 3, presents an all-optical scheme to generate a high-energy &gamma;-photon beam with large beam angular momentum (BAM), small divergence, and high brilliance.The image is based on original research by Hao Zhang et al. presented in their paper "Efficient bright &gamma;-ray vortex emission from a laser-illuminated light-fan-in-channel target", High Power Laser Science and Engineering 9 (3), 03000e43 (2021).

The image on the cover for Chinese Optics Letters Volume 19, Issue 10, reviews the important parameters including the refractive index detection range, resonance wavelength, and spectral sensitivity responsible for the sensing properties of PCF-SPR sensors.The image is based on original research by Chao Liu et al. presented in their paper "Overview of refractive index sensors comprising photonic crystal fibers based on the surface plasmon resonance effect [Invited]", Chinese Optics Letters 19 (10), 102202 (2021).

On the Cover
The techniques of high-speed communication and high-resolution display kit are both essential to modern life, as they constitute the foundations of those attractive concepts: Internet of Things, virtual/augmented reality, and metverse. If they are expected to be integrated, being realized simultaneously in one single device in the form of visible light communication (VLC) and micro-LED (μLED) array, it will be thrilling that this new technique would combine the advantages of both, such as avoiding occupying the limited electromagnetic sources, confidentiality, energy saving, and large color gamut, etc.
Photonics Research
• Nov. 26, 2021
• Vol. 9, Issue 11 (2021)
AP Highlights
Similar to electrons, photons can carry angular momentum (AM). In general, photonic AM consists of spin angular momentum (SAM) and orbital angular momentum (OAM). The former is associated with rotating electric field vector, while the latter is linked to swirling phase. SAM associated with circularly polarization has been known for a very long time and extensively exploited in a wide array of applications ranging from materials metrology, chiral molecule detection and quantum optics. About 30 years ago, Allen et al discovered that optical field with spiral phase wavefront possesses OAM, offered a whole new degree of freedom for photonics. To this point, the SAM and OAM of light studied are parallel to the propagation direction of the beam, hence can be termed as longitudinal SAM and longitudinal OAM. About a decade ago, the existence of transverse SAM in both free space and localized optical fields has been revealed via both theoretical and experimental works. Light with transverse SAM exhibits distinctively different behaviors when interact with matters, rendering another degree of freedom for photonic AM. In 2020, Zhan et al demonstrated the controllable generation of light pulses containing pure transverse OAM. The last piece of the puzzle for photonic AM is finally in place.
• Nov. 25, 2021
• Vol. 3, Issue 6 (2021)
Editors' Picks
Spatiotemporal (ST) wavepacket has been widely investigated since the invention of ultrafast laser. Conventional research on ST wavepackets focuses on studying spatiotemporal uncoupled wavepacket, meaning the space domain property and time domain property of the wavepacket are exploited separately.
Photonics Research
• Nov. 24, 2021
• Vol. 9, Issue 11 (2021)
Editors' Picks
The resonator is an important part of the laser oscillator. In general, it is very difficult to make a laser work ideally because it is quite difficult to adjust the two end mirrors of the resonator to a completely parallel state. Besides, when the cavity mirror of the resonator is slightly disturbed, the output of the laser will fluctuate greatly, even disappear. For all conventional plane-plane, plane-concave and concave-concave cavity lasers, these problems are inevitable. Poor prisms or cube-corner prisms have been used as the reflector of the laser resonator to improve the stability of the laser. In addition to alignment and power stability issues, the development of the movable resonator has special application values. The resonant beam charging (RBC) is a wireless power transfer technology which transfers power through the intra-cavity resonant beam. The mobility of the resonant cavity is the premise of the resonant beam charging system to realize the movable wireless power transmission. For the resonant beam charging system, the transmission power and efficiency when the output mirror moves along the axis of the resonant cavity have been demonstrated. However, the mobility of the resonant beam charging system along the horizontal direction needs further study.
Chinese Optics Letters
• Nov. 22, 2021
• Vol. 19, Issue 11 (2021)
On the Cover
Scientists have invented microrobots that can directly reach the site of disease to perform medical tasks. Microrobots-assisted in vivo drug delivery, release, and in situ surgery are therefore seen as very promising medical solutions. In recent years, more researchers are focusing on how microrobots can be truly applied for clinical therapy. Many in vivo experiments on small animals have also been carried out to validate and advance the in vivo application of the microrobots.
Chinese Optics Letters
• Nov. 17, 2021
• Vol. 19, Issue 11 (2021)
MTW-OPAL: a technology development platform for ultra-intense optical parametric chirped-pulse amplification systems

Optical parametric chirped-pulse amplification implemented using multikilojoule Nd:glass pump lasers is a promising approach for producing ultra-intense p

Optical parametric chirped-pulse amplification implemented using multikilojoule Nd:glass pump lasers is a promising approach for producing ultra-intense pulses (>1023 W/cm2). We report on the MTW-OPAL Laser System, an optical parametric amplifier line (OPAL) pumped by the Nd:doped portion of the multi-terawatt (MTW) laser. This midscale prototype was designed to produce 0.5-PW pulses with technologies scalable to tens of petawatts. Technology choices made for MTW-OPAL were guided by the longer-term goal of two full-scale OPALs pumped by the OMEGA EP to produce 2 × 25-PW beams that would be co-located with kilojoule-nanosecond ultraviolet beams. Several MTW-OPAL campaigns that have been completed since “first light” in March 2020 show that the laser design is fundamentally sound, and optimization continues as we prepare for “first-focus” campaigns later this year.show less

• Nov.28，2021
• High Power Laser Science and Engineering,Vol. 9, Issue 4
• 04000e63 (2021)
Monolithic thin film lithium niobate electro-optic modulator with over 110 GHz bandwidth

High-performance thin film lithium niobate (LN) electro-optic modulators with low cost are in demand. Based on photolithography and wet etching, we experi

High-performance thin film lithium niobate (LN) electro-optic modulators with low cost are in demand. Based on photolithography and wet etching, we experimentally demonstrate a thin film LN Mach–Zehnder modulator with a 3 dB bandwidth exceeding 110 GHz, which shows the potential of boosting the throughput and reducing cost. The fabricated modulator also exhibits a comparable low half-wave voltage-length product of $∼2.37 V·cm$, a high extinction ratio of $>23 dB$, and the propagation loss of optical waveguides of $∼0.2 dB/cm$. Besides, six-level pulse amplitude modulation up to $250 Gb/s$ is successfully achieved.show less

• Nov.28，2021
• Chinese Optics Letters,Vol. 20, Issue 2
• 022502 (2022)
Spectrally U-shaped profile of beam propagation factor in all-solid photonic bandgap fiber

We found the beam quality factor M2 of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap (PBG) of an all-solid

We found the beam quality factor M2 of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap (PBG) of an all-solid PBG fiber (AS-PBGF) for the first time, to the best of our knowledge, and our simulation results also match well with the phenomenon. The normal band that is near the high-frequency edge of the third PBG integrates the lowest M2 and single-mode operation simultaneously, while the other two edge regions suffer from anomalous variation of M2 versus wavelength. The general applicability of this finding can be further extended to other PBGs and also other representative structures in the AS-PBGF field.show less

• Nov.28，2021
• Chinese Optics Letters,Vol. 20, Issue 1
• 010602 (2022)
Enhancement of pre-pulse and picosecond pedestal contrast of the petawatt J-KAREN-P laser

We have experimentally improved the temporal contrast of the petawatt J-KAREN-P laser facility. We have investigated how the generation of pre-pulses by p

We have experimentally improved the temporal contrast of the petawatt J-KAREN-P laser facility. We have investigated how the generation of pre-pulses by post-pulses changes due to the temporal overlap between the stretched pulse and the post-pulse in a chirped-pulse amplification system. We have shown that the time at which the pre-pulse is generated by the post-pulse and its shape are related to the time difference between the stretched main pulse and the post-pulse. With this investigation, we have found and identified the origins of the pre-pulses and have demonstrated the removal of most pre-pulses by eliminating the post-pulse with wedged optics. We have also demonstrated the impact of stretcher optics on the picosecond pedestal. We have realized orders of magnitude enhancement of the pedestal by improving the optical quality of a key component in the stretcher.show less

• Nov.28，2021
• High Power Laser Science and Engineering,Vol. 9, Issue 4
• 04000e62 (2021)

We report on experimental observation of non-laminar proton acceleration modulated by strong magnetic field in laser irradiating micron-meter Aluminum targets. The results illustrate co

We report on experimental observation of non-laminar proton acceleration modulated by strong magnetic field in laser irradiating micron-meter Aluminum targets. The results illustrate coexistence of ring-like and filamentation structures. We implement the knife edge method into the radiochromic film detector to map the accelerated beams, measuring source size of 30 ~ 110 μm for proton of > 5MeV. The diagnosis reveals that the ring-like profile originates from low energy protons far off the axis while the filamentation is from the near-axis high energy protons, exhibiting non-laminar features. Particle-in-cell simulations reproduced the experimental results, showing that the short-term magnetic turbulence via Weibel instability and the long-term quasi-static annular magnetic field by the streaming electric current account for the measured beam profile. Our work provides direct mapping of laser-driven proton sources in the space-energy domain and reveals the non-laminar beam evolution at featured time scales.show less

• Nov.28，2021
• High Power Laser Science and Engineering

We report on compact and robust supercontinuum generation and post-compression using transmission of light through multiple thin solid plates at the SwissFEL x-ray free-electron laser f

We report on compact and robust supercontinuum generation and post-compression using transmission of light through multiple thin solid plates at the SwissFEL x-ray free-electron laser facility. A single stage consisting of three thin plates followed by a chirped mirror compressor achieves compression of initially 30 fs pulses with 800 nm center wavelength to sub-10 fs duration. We also demonstrate a two-stage implementation to compress the pulses further to sub-5 fs duration. With the two-stage setup, the generated supercontinuum includes wavelengths ranging from 500 nm to 1100 nm. The multi-plate setup is compact, robust, and stable which makes it ideal for applications at free-electron laser facilities such as pump-probe experiments and laser-arrival timing tools.show less

• Nov.28，2021
• High Power Laser Science and Engineering

We demonstrate the stabilization of optical frequency combs (OFCs) using a segment of fiber delay line as reference. An Er-doped fiber mode-locked laser is phase locked to a kilometer-l

We demonstrate the stabilization of optical frequency combs (OFCs) using a segment of fiber delay line as reference. An Er-doped fiber mode-locked laser is phase locked to a kilometer-long fiber delay line using three different schemes. The short-term stability of the comb modes in the OFC stabilized by these schemes are obviously enhanced, down to 10<sup>-12</sup> level at millisecond average time. Among these three schemes, phase locking two bunches of comb modes in the OFC to the same fiber delay line exhibits the lowest residual phase noise. Fiber-delay-line-referenced optical frequency combs can provide reliable laser sources in precise metrology owing to its advances of low-cost, compactness and highly-integration.show less

• Nov.28，2021
• Chinese Optics Letters,Vol. 20, Issue 2
• (2022)

Kalman filtering (KF) has good potential in fast rotation of state of polarization (RSOP) tracking. Different measurement equations cause the diverse RSOP tracking performances. We comp

Kalman filtering (KF) has good potential in fast rotation of state of polarization (RSOP) tracking. Different measurement equations cause the diverse RSOP tracking performances. We compare the conventional KF (CKF) and the modified KF (MKF)that have different measurement equations. Semi-theoretical analysis indicates the lower conditional variances of measurement residual and process noise of MKF. Compared with CKF, the MKF has > 3-dB optical signal-to-noise ratio (OSNR) improvement at the 10-MHz scrambling rate in simulation. For MKF, more significant tracking speed improvement exists in lower OSNR. MKF can be smoothly combined with adaptive algorithm, which outperforms adaptive CKF throughout the simulations.show less

• Nov.28，2021
• Chinese Optics Letters,Vol. 20, Issue 2
• (2022)
Guilin, ChinaAugust 25-27, 2021
The image on the cover for Chinese Optics Letters Volume 19, Issue 11, summarizes the PAI techniques, imaging systems, and their biomedical applications in microrobots tracking in vitro and in vivo. From a robotic tracking perspective, some insight into the future of PAI technology in clinical applications is also provided.The image is based on original research by Dengfeng Li et al. presented in their paper "Review of photoacoustic imaging for microrobots tracking in vivo [Invited]", Chinese Optics Letters 19 (11), 111701 (2021).
• Journal
• 19th Nov，2021
The image on the cover for Photonics Research Volume 9, Issue 11, proposes a device that could be used for both display and visible light communication (VLC) applications. The semipolar blue &mu;LED array fabricated in this study shows a negligible wavelength shift, indicating a significant reduction in the quantum confined Stark effect. The image is based on original research by Tingzhu Wu et al. presented in their paper "Highly stable full-color display device with VLC application potential using semipolar &mu;LEDs and all-inorganic encapsulated perovskite nanocrystal", Photonics Research 9 (11), 11002132 (2021).
• Journal
• 19th Nov，2021