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Abstract In current documented studies, it has been observed that wavelength converters utilizing AlGaAsOI waveguides exhibit suboptimal on-chip wavelength conversion efficiency from the C-band to the 2 μm band, generally falling below −20.0 dB. To address this issue, we present a novel wavelength conversion device assisted by a waveguide amplifier, incorporating both AlGaAs wavelength converter and erbium-ytterbium co-doped waveguide amplifier, thereby achieving a notable conversion efficiency exceeding 0 dB. The noteworthy enhancement in efficiency can be attributed to the specific dispersion design of the AlGaAs wavelength converter, which enables an upsurge in conversion efficiency to −15.54 dB under 100 mW of pump power. Furthermore, the integration of an erbium-ytterbium co-doped waveguide amplifier facilitates a loss compensation of over 15 dB. Avoiding the use of external optical amplifiers, this device enables efficient and high-bandwidth wavelength conversion, showing promising applications in various fields, such as optical communication, sensing, imaging, and beyond. Graphical Abstract

Abstract In recent years, contrastive language‐image pre‐training (CLIP) has gained popularity for processing 2D data. However, the application of cross‐modal transferable learning to 3D data remains a relatively unexplored area. In addition, high‐quality, labelled point cloud data for Mechanical, Electrical, and Plumbing (MEP) scenarios are in short supply. To address this issue, the authors introduce a novel object detection system that employs 3D point clouds and 2D camera images, as well as text descriptions as input, using image‐text matching knowledge to guide dense detection models for 3D point clouds in MEP environments. Specifically, the authors put forth the proposition of a language‐guided point cloud modelling (PCM) module, which leverages the shared image weights inherent in the CLIP backbone. This is done with the aim of generating pertinent category information for the target, thereby augmenting the efficacy of 3D point cloud target detection. After sufficient experiments, the proposed point cloud detection system with the PCM module is proven to have a comparable performance with current state‐of‐the‐art networks. The approach has 5.64% and 2.9% improvement in KITTI and SUN‐RGBD, respectively. In addition, the same good detection results are obtained in their proposed MEP scene dataset.

A length of polarization-correlation (LPC) based on speckle pattern of the non-uniform spatial polarization distribution is proposed and measured by using the classical measurement method of the Stokes polarization parameters for optical coherent detection. The LPC, which depends on the material of the scattering medium, is emphasized on the speckle scale. A gradually expanding window centered at the brightest spot of the speckle pattern, is designed to calculate the degree of polarization (DOP) of different speckle sizes. Moreover, the magnitude of LPC is equal to the speckle size that reaches a particular threshold on the DOP curve. It is experimentally demonstrated that the LPC is exploited to not only investigate the nature of the polarization changes between different speckle sizes, but also be combined with coherent efficiency. This study can provide new insights of speckle depolarization in optical coherent detection and open new opportunities for improving coherent efficiency.

Silicon-based optoelectronics (SBO), combining the advantages of both microelectronics and optoelectronics, has entered a period of rapid development. Applications based on SBO have expanded from traditional communication field to other fields such as sensing, computing, and artificial intelligence. Although the SBO technology started relatively late in China, it has developed rapidly in recent years due to continuous investment and improved industrial structure. This article first reviews the early activities, and then, summarizes the current status of SBO in China. It provides a comprehensive analysis of academic and industrial advancements in recent years and discusses future development directions and main challenges.

In microgravity, atoms can be prepared to a lower temperature and manipulated with a longer time. The Cold Atom Physics Research Rack (CAPR) in Chinese Space Station, which aims to prepare quantum degenerate gas for deep cooling and quantum simulation in microgravity, has been designed, realized, and validated. We built an integrated CAPR, consisting of a physical system, an all-fiber 780 nm laser system and a low phase noise 1064 nm fiber laser system, and an electrical driving and controlling system. With the CAPR, a 87Rb quantum degenerate gas with 1.2 × 105 atoms and a temperature below 30 nK was achieved on ground. In this article, we also show the robustness of the rack, based on the experimental results before and after the simulation of the vibration and impact during the launch.

Abstract Aerosols and clouds greatly affect the Earth’s radiation budget and global climate. Light detection and ranging (lidar) has been recognized as a promising active remote sensing technique for the vertical observations of aerosols and clouds. China launched its first space-borne aerosol-cloud high-spectral-resolution lidar (ACHSRL) on April 16, 2022, which is capable for high accuracy profiling of aerosols and clouds around the globe. This study presents a retrieval algorithm for aerosol and cloud optical properties from ACHSRL which were compared with the end-to-end Monte-Carlo simulations and validated with the data from an airborne flight with the ACHSRL prototype (A2P) instrument. Using imaging denoising, threshold discrimination, and iterative reconstruction methods, this algorithm was developed for calibration, feature detection, and extinction coefficient (EC) retrievals. The simulation results show that 95.4% of the backscatter coefficient (BSC) have an error less than 12% while 95.4% of EC have an error less than 24%. Cirrus and marine and urban aerosols were identified based on the airborne measurements over different surface types. Then, comparisons were made with U.S. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) profiles, Moderate-resolution Imaging Spectroradiometer (MODIS), and the ground-based sun photometers. High correlations (R > 0.79) were found between BSC (EC) profiles of A2P and CALIOP over forest and town cover, while the correlation coefficients are 0.57 for BSC and 0.58 for EC over ocean cover; the aerosol optical depth retrievals have correlation coefficient of 0.71 with MODIS data and show spatial variations consistent with those from the sun photometers. The algorithm developed for ACHSRL in this study can be directly employed for future space-borne high-spectral-resolution lidar (HSRL) and its data products will also supplement CALIOP data coverage for global observations of aerosol and cloud properties.

Abstract Background Bronchial rupture in children is a rare but dangerous complication after chest trauma and is associated with increased mortality. Veno-venous (V-V) extracorporeal membrane oxygenation (ECMO) is reported as one of the treatments for this life-threatening complication. Case presentation A 4-year-old boy with bronchial rupture and traumatic wet lung complicated by cardiac arrest after chest trauma was admitted to an adult ECMO centre. He experienced two cardiac arrests, one before and one during the operation. The total duration of cardiac arrest was 30 min. V-V ECMO was initiated because of severe hypoxia and hypercapnia during the operation. ECMO was performed for 6 days, and mechanical ventilation lasted 11 days. On the 31st day after surgery, he had recovered completely and was discharged without neurological deficit. Conclusion V-V ECMO can be considered for supportive care in children with severe acute respiratory failure after bronchial rupture. In an emergency, V-V ECMO can be carried out effectively in a qualified and experienced adult ECMO centre. However, the application of ECMO in children is different from that in adults and requires more refined management.

A continuous-wave (CW) single-longitudinal-mode (SLM) Raman laser at 1240 nm with power of up to 20.6 W was demonstrated in a free-running diamond Raman oscillator without any axial-mode selection elements. The SLM operation was achieved due to the spatial-hole-burning free nature of Raman gain and was maintained at the highest available pump power by suppressing the parasitic stimulated Brillouin scattering (SBS). A folded-cavity design was employed for reducing the perturbing effect of resonances at the pump frequency. At a pump power of 69 W, the maximum Stokes output reached 20.6 W, corresponding to a 30% optical-to-optical conversion efficiency from 1064 to 1240 nm. The result shows that parasitic SBS is the main physical process disturbing the SLM operation of Raman oscillator at higher power. In addition, for the first time, the spectral linewidth of a CW SLM diamond Raman laser was resolved using the long-delayed self-heterodyne interferometric method, which is 105 kHz at 20 W.

Measuring the characteristics of seawater constituent is in great demand for studies of marine ecosystems and biogeochemistry. However, existing techniques based on remote sensing or in situ samplings present various tradeoffs with regard to the diversity, synchronism, temporal-spatial resolution, and depth-resolved capacity of their data products. Here, we demonstrate a novel oceanic triple-field-of-view (FOV) high-spectral-resolution lidar (HSRL) with an iterative retrieval approach. This technique provides, for the first time, comprehensive, continuous, and vertical measurements of seawater absorption coefficient, scattering coefficient, and slope of particle size distribution, which are validated by simulations and field experiments. Furthermore, it depicts valuable application potentials in the accuracy improvement of seawater classification and the continuous estimation of depth-resolved particulate organic carbon export. The triple-FOV HSRL with high performance could greatly increase the knowledge of seawater constituents and promote the understanding of marine ecosystems and biogeochemistry.

The phase summation effect in sum-frequency mixing process is utilized to avoid a nonlinearity obstacle in the power scaling of single-frequency visible or ultraviolet lasers. Two single-frequency fundamental lasers are spectrally broadened by phase modulation to suppress stimulated Brillouin scattering in fiber amplifier and achieve higher power. After sum-frequency mixing in a nonlinear optical crystal, the upconverted laser returns to single frequency due to phase summation, when the phase modulations on two fundamental lasers have a similar amplitude but opposite sign. The method was experimentally proved in a Raman fiber amplifier-based laser system, which generated a power-scalable sideband-free single-frequency 590 nm laser. The proposal manifests the importance of phase operation in wave-mixing processes for precision laser technology.

Compared with Yb, Nd has potential in 1120 nm fiber lasers, with the characteristics of larger emission cross section and four-level structure. In this work, Nd-doped fiber (NDF) oscillator and Nd-Raman fiber (NRF) oscillator were built using single-mode 5/125 NDF to study the lasing characteristics at 1120 nm, especially the suppression of amplified spontaneous emission at 1060 nm. Limited by the parasitic oscillation at 1060 nm, the NDF oscillator achieved 5 W output at 1120 nm. The NRF oscillator removed the limitation due to the Raman shift from 1064 nm to 1120 nm and obtained an output of 7.7 W at 1120 nm with a spectral peak-to-peak contrast of 36 dB. This work provides experimental basis for the application of NDF in 1.1 μm.

The efficacy of underwater laser detection is considerably impacted by the intense attenuation of light resulting from the scattering and absorption effects of water. In this study, we present the simulation and design of the underwater Lidar system that integrates the paraxial multi-channel detection strategy to enhance the dynamic range in subsea environments. To evaluate the performance of the system with multiple detection channels, we introduce a multi-channel underwater Lidar simulation (MULS) method based on the radiative transfer Lidar equations. Experimental validations were conducted under varied water conditions to assess the performance of the prototype and validate the simulation results. The measured range accuracy of each channel in the prototype is better than 0.1085 m, and the simulated and measured waveforms exhibit strong correlations, verifying the reliability and validity of the simulation method. The effects of transceiver configuration and the maximum detectable range of different detection methods were also discussed. Preliminary results indicate that the paraxial multi-channel design effectively suppresses near-field backscattering and substantially enhances the maximum detectable range. The findings presented in this study may provide valuable insights for the design and optimization of future underwater laser detection systems.

High-power ns-pulsed lasers have been widely used in many significant applications, including laser radar, remote-sensing, biomedicine, industrial process, and military defense. Stimulated Raman scattering (SRS) provides an efficient method for extending the wavelengths of laser radiation. Due to the excellent thermal conductivity, high damage threshold, and high gain coefficient, diamond crystal is considered the most potential SRS material to address laser output in specific wavelength regions with high power, high beam quality, and high conversion efficiency. This paper reviews the advances of ns-pulsed crystalline Raman lasers and particularly emphasizes the progress of ns-pulsed diamond Raman lasers (DRLs) in the past decade. DRL has demonstrated a maximum peak power of 1.2 MW at 1.240 μm with a pulse duration of 8 ns. It can also generate high-energy ns pulses featuring Fourier-limited spectral linewidth. The superior optical characteristics and the mature technology of synthetic diamond crystal will make DRL a promising technique to achieve higher performance ns laser pulses.

The Cold Atom Physics Rack (CAPR) of Chinese space station will be launched at the end of 2022. The important goal of CAPR is to achieve BEC at 100 pk. In order to obtain ultracold atoms in microgravity of space station, we propose a two-stage cooling scheme using all-optical trap with different waist beams. The cold atom cloud obtained by this scheme is composed of condensate and thermal atoms around condensate. The design of our two-stage cooling scheme will effectively reduce the temperature of the thermal atom cloud and the effective temperature generated by the interaction energy of the condensate. The atomic temperature of 5 nk is obtained from the ground test experiment, and the corresponding temperature under the microgravity condition of the space station is theoretically predicted to be less than 100 pk. Taking the advantages of ultracold temperature and long-time detection, many scientific experiments will be arranged. In this paper, the ground test experiments based on ground principle prototype and pre-prototype for CAPR are also introduced.

A tunable and narrow-bandwidth Q-switched ytterbium-doped fiber (YDF) laser is investigated in this paper. The non-pumped YDF acts as a saturable absorber and, together with a Sagnac loop mirror, provides a dynamic spectral-filtering grating to achieve a narrow-linewidth Q-switched output. By adjusting an etalon-based tunable fiber filter, a tunable wavelength from 1027 nm to 1033 nm is obtained. When the pump power is 1.75 W, the Q-switched laser pulses with a pulse energy of 10.45 nJ, and a repetition frequency of 11.98 kHz and spectral linewidth of 112 MHz are obtained. This work paves the way for the generation narrow-linewidth Q-switched lasers with tunable wavelengths in conventional ytterbium, erbium, and thulium fiber bands to address critical applications such as coherent detection, biomedicine, and nonlinear frequency conversion.

A thermal model concerning resonantly pumped high power Tm-doped fiber amplifiers is established with temperature dependent parameters taken into consideration. With this model, performance of resonantly pumped Tm-doped fiber amplifiers at 1 kW output is investigated. Comparisons with the traditional 793 nm LD pump scheme shows that, resonant pumping, especially the 1.9 μm pump, is more favorable for high power Tm-doped fiber systems, featuring high operation efficiency with low heat load, limited temperature rise, controllable beam compression and a relatively small laser intensity at the output end. Besides, the power scalability of resonantly pumped Tm-doped fiber systems with 25/250 double-clad fiber is also explored numerically with various thermal effects, optical damage and nonlinear effects taken in account. Simulations show that, for 1 GHz narrow linewidth output, outer cladding damage and stimulated Brillouin scattering are the two primary limiting factors for power scaling. And, the maximal output of a Tm-doped fiber amplifier could reach 5.1 kW and 6.8 kW for 1.6 μm pump and 1.9 μm pump, respectively. For systems with broad spectrum, output approaching 10 kW can be expected.

The laser heterodyne radiometer (LHR) has the advantages of miniaturization, low cost, and high spectral-resolution as a ground-verification instrument for satellite observation of atmospheric trace-gas concentration. To verify the accuracy of LHR measurements, a new performance evaluation method is presented here, based on an ASE source and a CO2 absorption cell in the laboratory. Preliminary simulation analysis based on the system parameters of LHR is carried out for the performance analysis and data processing of this new combined test system. According to the simulation results, at wavelength deviation of fewer than 30 MHz, the retrieval error, which increases with bandwidth, can obtain an accuracy of 1 ppm within the bandwidth range of the photodetector (1.2 GHz) when this instrument line shape (ILS) is calibrated. Meanwhile, when the filter bandwidth is less than 200 MHz, the maximum error without ILS correction does not exceed 0.07 ppm. Moreover, with an ideal 60 MHz bandpass filter without ILS correction, LHR’s signal-to-noise ratio (SNR) should be greater than 20 to achieve retrieval results of less than 1 ppm. When the SNR is 100, the retrieval error is 0.206 and 0.265 ppm, corresponding to whether the system uncertainties (temperature and pressure) are considered. Considering all the error terms, the retrieval error (geometrically added) is 0.528 ppm at a spectral resolution of 0.004 cm−1, which meets the measurement accuracy requirement of 1 ppm. In the experiment, the retrieval and analysis of the heterodyne signals are performed for different XCO2 with [400 ppm, 420 ppm] in the absorption cell. Experimental results match well with the simulation, and confirm the accuracy of LHR with an error of less than 1 ppm with an SNR of 100. The LHR will be used to measure atmospheric-CO2 column concentrations in the future, and could be effective validation instruments on the ground for spaceborne CO2-sounding sensors.

Accurate monitoring of atmospheric carbon dioxide (CO2) is of great significance for studying the carbon cycle. Compared to ground observational sites, airborne observations cover a wider area, which help in effectively monitoring the distribution of CO2 sources and sinks. In this study, an airborne campaign was carried out in June and July 2021 to measure the atmospheric CO2 concentration over a desert site, Dunhuang, located in western China. The dry-air column-averaged CO2 mole fraction (XCO2) inversion results obtained from the Atmospheric Carbon Dioxide Lidar (ACDL) system were compared with the Orbiting Carbon Observatory 2 (OCO-2) retrievals, portable Fourier Transform Spectrometer (EM27/SUN) measurement results, and with the XCO2 estimates derived using the airborne Ultraportable Greenhouse Gas Analyzer (UGGA) and the Copernicus Atmosphere Monitoring Service (CAMS) model measurements. Moreover, the vertical CO2 profiles obtained from the OCO-2 and the CAMS datasets were also compared with the airborne UGGA measurements. OCO-2 and CAMS CO2 measurements showed a vertical distribution pattern similar to that of the aircraft-based measurements of atmospheric CO2. In addition, the relationship of atmospheric CO2 with the aerosol optical depth (AOD) was also determined and the results showed a strong and positive correlation between the two variables.

Attenuation of the laser beam in underwater transmission and detection due to absorption and scattering results in a rapid reduction in energy and blurring of the image. By combining the bidirectional reflectivity distribution function (BRDF) with the Monte Carlo (MC) method, a full-link underwater imaging process model was established which comprehensively investigated the influence of water quality, transmission distance and target characteristics on imaging performance. In order to describe the transmission process of the light more accurately, by adding particles with both absorption and scattering functions in the medium, the Mie scattering theory was employed to simulate the real channel. Moreover, while setting the gate width, the pre-calibrated detector response curve was employed to build a corresponding relationship between the image grayscale and the detector collection energy, aiming to simulate the working mode of the detector in the experiment. In various imaging scenarios, the maximum relative errors between the simulated images and experimental results were within 30%, which proved the correctness of the imaging simulation model and the feasibility of the imaging MC (IMC) method to evaluate the quality of whole imaging process.

Over the last two decades, Geiger-mode lidar (GML) systems have been developing rapidly in defense and commercial applications, demonstrating high point density and great collection efficiency. We presented a circular scanning GML system simulation model for performance prediction and developed a GML system for civilian mapping. The lidar system used an eye-safe fiber laser at 1545 nm coupled with a 64 × 64 pixels photon-counting detector array. A real-time data compression algorithm was implanted to reduce half of the data transmission rate and storage space compared to the uncompressing situation. The GML system can operate at aircraft above-ground levels (AGLs) between 0.35 km and 3 km, and at speeds in excess of 220 km/h. The initial flight tests indicate that the GML system can operate day and night with an area coverage of 366 km2/h. The standard deviations of the relative altimetric accuracy and the relative planimetric accuracy are 0.131 m and 0.152 m, respectively. The findings presented in this article guide the implementation of designing an airborne GML system and the data compression method.

In this paper, we present a high-energy, narrow pulse-width, long-wave infrared laser based on a ZnGeP2 (ZGP) optical parametric oscillator (OPO). The pump source is a 2.1 μm three -stage Ho:YAG master oscillator power-amplifier (MOPA). At a repetition frequency of 1 kHz, the Ho:YAG MOPA system outputs the maximal average power of 52.1 W, which corresponds to the shortest pulse width of 14.40 ns. By using the Ho:YAG MOPA system as the pump source, the maximal average output powers of 3.15 W at 8.2 μm and 11.4 W at 2.8 μm were achieved in a ZGP OPO. The peak wavelength and linewidth (FWHM) of the long-wave infrared laser were 8156 nm and 270 nm, respectively. At the maximal output level, the pulse width and beam quality factor M2 were measured to be 8.10 ns and 6.2, respectively.

The spaceborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system was found to be helpful in observing atmospheric CO2 and understanding the carbon cycle. The airborne experiments of a scale prototype of China’s planned spaceborne IPDA LIDAR was implemented in 2019. A problem with data inversion caused by the detector module nonlinearity was found. Through many experiments, the amplifier circuit board (ACB) of the detector module was proved to be the main factor causing the nonlinearity. Through amplifier circuit optimization, the original bandwidth of the ACB was changed to 1 MHz by using a fifth-order active filter. Compared with the original version, the linearity of optimized ACB is improved from 42.6% to 0.0747%. The optimized ACB was produced and its linearity was verified by experiments. In addition, the output waveform of the optimized ACB changes significantly, which will affect the random error (RE) of the optimized IPDA LIDAR system. Through the performance simulation, the RE of more than 90% of the global area is less than 0.728 ppm. Finally, the transfer model of the detector module was given, which will be helpful for the further optimization of the CO2 column-averaged dry-air mixing ratio (XCO2) inversion algorithm.

Abstract Intravascular photoacoustic-ultrasound (IVPA-US) imaging is an emerging hybrid modality for the detection of lipid-laden plaques, as it provides simultaneous morphological and lipid-specific chemical information of an artery wall. Real-time imaging and display at video-rate speed are critical for clinical utility of the IVPA-US imaging technology. Here, we demonstrate a portable IVPA-US system capable of imaging at up to 25 frames per second in real-time display mode. This unprecedented imaging speed was achieved by concurrent innovations in excitation laser source, rotary joint assembly, 1 mm IVPA-US catheter size, differentiated A-line strategy, and real-time image processing and display algorithms. Spatial resolution, chemical specificity, and capability for imaging highly dynamic objects were evaluated by phantoms to characterize system performance. An imaging speed of 16 frames per second was determined to be adequate to suppress motion artifacts from cardiac pulsation for in vivo applications. The translational capability of this system for the detection of lipid-laden plaques was validated by ex vivo imaging of an atherosclerotic human coronary artery at 16 frames per second, which showed strong correlation to gold-standard histopathology. Thus, this high-speed IVPA-US imaging system presents significant advances in the translational intravascular and other endoscopic applications.

Among the various challenges that spaceborne radar observations of the ocean face, the following two issues are probably of a higher priority: inadequate dynamic resolution, and ineffective vertical penetration. It is therefore the vision of the National Laboratory for Marine Science and Technology of China that two highly anticipated breakthroughs in the coming decade are likely to be associated with radar interferometry and ocean lidar (OL) technology, which are expected to make a substantial contribution to a submesoscale-resolving and depth-resolving observation of the ocean. As an expanded follow-up of SWOT and an oceanic counterpart of CALIPSO, the planned “Guanlan” science mission comprises a dual-frequency (Ku and Ka) interferometric altimetry (IA), and a near-nadir pointing OL. Such an unprecedented combination of sensor systems has at least three prominent advantages. (i) The dual-frequency IA ensures a wider swath and a shorter repeat cycle which leads to a significantly improved temporal and spatial resolution up to days and kilometers. (ii) The first spaceborne active OL ensures a deeper penetration depth and an all-time detection which leads to a layered characterization of the optical properties of the subsurface ocean, while also serving as a near-nadir altimeter measuring vertical velocities associated with the divergence, and convergence of geostrophic eddy motions in the mixed layer. (iii) The simultaneous functioning of the IA/OL system allows for an enhanced correction of the contamination effects of the atmosphere and the air-sea interface, which in turn considerably reduces the error budgets of the two sensors. As a result, the integrated IA/OL payload is expected to resolve the ocean variability at submeso and sub-week scales with a centimeter-level accuracy, while also partially revealing marine life systems and ecosystems with a 10-m vertical interval in the euphotic layer, moving a significant step forward toward a “transparent ocean” down to the vicinity of the thermocline, both dynamically and bio-optically.

Ocean water column information profiles are essential for ocean research. Currently, water column profiles are typically obtained by ocean lidar instruments, including spaceborne, airborne and shipborne lidar, most of which are equipped with a 532 nm laser; however, blue wavelength penetrates more for open ocean detection. In this paper, we present a novel airborne dual-wavelength ocean lidar (DWOL), equipped with a 532 and 486 nm laser that can operate simultaneously. This instrument was designed to compare the performance of 486 and 532 nm lasers in a single detection area and to provide a reference for future spaceborne oceanic lidar (SBOL) design. Airborne and shipborne experiments were conducted in the South China Sea. Results show that—for a 500-frame accumulation—the 486 nm channel obtained volume profiles from a depth of approximately 100 m. In contrast, the vertical profiles obtained by the 532 nm channel only reached in a depth of 75 m, which was approximately 25% less than that of 486 m channel in the same detection area. Results from the inverse lidar attenuation coefficient α(z) for the DWOL show that the maximum value of α(z) ranged from 40 to 80 m, which was consistent with the chlorophyll-scattering layer (CSL) distribution measured by the shipborne instrument. Additionally, α486(z) decreased for depth beyond 80 m, indicating that the 486 nm laser can potentially penetrate the entire CSL.

To overcome the retrieval problems in complex water, dual working wavelengths are required instead of a single wavelength in oceanic lidar. The wavelength optimization method of detecting chlorophyll a and Colored Dissolved Organic Matter (CDOM) absorption coefficient with a dual-wavelength lidar is studied in this paper. The inversion methods of chlorophyll a and CDOM absorption are developed based on the water absorption characteristics, which then lead to the inversion error equations. The effects of the wavelength on the inversion errors are studied. For the case in which λ1 and λ2 are both random, the errors are relatively small when λ1 is chosen between 420 and 560 nm and λ2 is selected under 420 nm. For the case in which λ1 is fixed at 532 nm, the errors generally decrease with decreasing λ2, with minimums around 300 and 356–360 nm under different water conditions. The wavelength optimization method discussed in this paper and the penetration depth criterion will be beneficial to the design of the dual-wavelength lidar.

As one of the most influential greenhouse gases, carbon dioxide (CO2) has a profound impact on the global climate. The spaceborne integrated path differential absorption (IPDA) lidar will be a great sensor to obtain the columnar concentration of CO2 with high precision. This paper analyzes the performance of a spaceborne IPDA lidar, which is part of the Aerosol and Carbon Detection Lidar (ACDL) developed in China. The line-by-bine radiative transfer model was used to calculate the absorption spectra of CO2 and H2O. The laser transmission process was simulated and analyzed. The sources of random and systematic errors of IPDA lidar were quantitatively analyzed. The total systematic errors are 0.589 ppm. Monthly mean global distribution of relative random errors (RREs) was mapped based on the dataset in September 2016. Afterwards, the seasonal variations of the global distribution of RREs were studied. The global distribution of pseudo satellite measurements for a 16-day orbit repeat cycle showed relatively uniform distribution over the land of the northern hemisphere. The results demonstrated that 61.24% of the global RREs were smaller than 0.25%, or about 1 ppm, while 2.76% of the results were larger than 0.75%. The statistics reveal the future performance of the spaceborne IPDA lidar.

The demand for greenhouse gas measurement has increased dramatically due to global warming. A 1.57-μm airborne double-pulse integrated-path differential absorption (IPDA) light detection and ranging (LIDAR) system for CO2 concentration measurement was developed. The airborne field experiments of this IPDA LIDAR system were conducted at a flight altitude of approximately 7 km, and the weak echo signal of the ocean area was successfully received. The matched filter algorithm was applied to the retrieval of the weak signals, and the pulse integration method was used to improve the signal-to-noise ratio. The inversion results of the CO2 column-averaged dry-air mixing ratio (XCO2) by the scheme of averaging after log (AVD) and the scheme of averaging signals before log were compared. The AVD method was found more effective for the experiment. The long-term correlation between the changing trends of XCO2 retrieved by the IPDA LIDAR system and CO2 dry-air volume mixing ratio measured by the in-situ instrument reached 92%. In the steady stage of the open area (30 km away from the coast), which is almost unaffected by the residential areas, the mean value of XCO2 retrieved by the IPDA LIDAR system was 414.69 ppm, with the standard deviation being 1.02 ppm. Compared with the CO2 concentration measured by the in-situ instrument in the same period, bias was 1.30 ppm. The flight path passed across the ocean, residential, and mountainous areas, with the mean value of XCO2 of the three areas being 419.35, 429.29, and 422.52 ppm, respectively. The gradient of the residential and ocean areas was 9.94 ppm, with that of the residential and mountainous areas being 6.77 ppm. Obvious gradients were found in different regions.

A cloud structure construction algorithm adapted for the nighttime condition is proposed and evaluated. The algorithm expands the vertical information inferred from spaceborne radar and lidar via matching of infrared (IR) radiances and other properties at off-nadir locations with their counterparts that are collocated with active footprints. This nighttime spectral radiance matching (NSRM) method is tested using measurements from CloudSat/Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Moderate Resolution Imaging Spectroradiometer (MODIS). Cloud layer heights are estimated up to 400 km on both sides of the ground track and reconstructed with the dead zone setting for an approximate evaluation of the reliability. By mimicking off-nadir pixels with a dead zone around pixels along the ground track, reconstruction of nadir profiles shows that, at 200 km from the ground track, the cloud top height (CTH) and the cloud base height (CBH) reconstructed by the NSRM method are within 1.49 km and 1.81 km of the original measurements, respectively. The constructed cloud structure is utilized for cloud classification in the nighttime. The same method is applied to the daytime measurements for comparison with collocated MODIS classification based on the International Satellite Cloud Climatology Project (ISCCP) standard. The comparison of eight cloud types over the expanded distance shows good agreement in general.

The analytical model based on the quasi-single small-angle scattering approximation can efficiently simulate oceanic lidar signals with multiple scattering; thus, its accuracy is of particular interest to scientists. In this paper, the model is modified to include refraction at oblique incidence and is then compared with Monte Carlo (MC) simulations and experimental results. Under different conditions, the results calculated by the analytical model demonstrate good agreement with the MC simulation and experimental data. The coefficient of determination R2 considering the logarithm of signals and the root mean square of the relative difference δ are R2 = 0.998 and δ = 10% in comparison with the semi-analytic MC simulation and R2 = 0.952 and δ = 46% for the lidar experiment. Thus, the results demonstrate the validity of the analytical model in the simulation of oceanic lidar signals.

A narrow-linewidth 793-nm diode-pumped Tm3+ -doped double-clad silica fiber laser operated at 2 μm and actively Q-switched with an acousto-optic modulator is reported. Using a fiber Bragg grating as an output coupler, approximately 0.1-nm linewidth at 1996.8-nm pulses is derived at 80-kHz repetition rate. The maximum average output power is above 2 W for 11.6-W absorbed pump power. Less than 150-ns pulse is obtained at the repetition rate of 30 kHz. The laser is a promising seed laser for amplification in a master oscillator power amplifier system.

On April 16, 2022, China has successfully launched the world's first space-borne high spectral resolution lidar (HSRL), which is called the Aerosol Carbon Detection Lidar (ACDL) onboard the DQ-1 satellite. The ACDL is expected to precisely detect the three-dimensional distribution of aerosol and cloud globally with high spatial-temporal resolutions. To assess the performance of the newly launched satellite lidar, the ACDL retrieved observations were compared with groundbased lidar measurements of atmospheric aerosol and cloud over northwest China from May to July 2022 by the exploitation of the Belt and Road lidar network (BR-lidarnet) initiated by Lanzhou University of China, as well as CALIPSO lidar observations. A total of six cases at daytime and nighttime, including clear days, dust events, and cloudy conditions, were selected for further analysis. Moreover, profiles of total attenuated backscatter coefficient (TABC) and volume depolarization ratio (VDR) at 532 nm measured by the ACDL, CALIPSO lidar and ground-based lidar are compared in detail. Comparison between the 532 nm extinction coefficient and lidar ratio obtained from ACDL HSRL retrieval and the Raman retrieval results obtained from BR-lidarnet. The achieved results revealed that the ACDL observations were in good agreement with the ground-based lidar measurements during dust events with a relative deviation of about -10.5 ± 25.4 % for the TABC and -6.0 ± 38.5 % for the VDR. Additionally, the heights of cloud top and bottom from these two measurements were well matched and comparable. Compared with the observation of CALIPSO, it also shows high consistency. This study proves that the ACDL provides reliable observations of aerosol and cloud in the presence of various climatic conditions, which helps to further evaluate the impacts of aerosol on climate and environment as well as the ecosystem in the future. [ABSTRACT FROM AUTHOR]

The atmospheric environment monitoring satellite DQ-1 was launched in April 2022, which consists of a spaceborne High Spectral Resolution Lidar (HSRL) system. This new system enables the accurate measurements of global aerosol optical properties, which can be used in Geo-scientific community after the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) retirement. Developing a suitable retrieval algorithm and validating retrieved results are prominently needed. This research demonstrates a retrieval algorithm for aerosol optical properties using the DQ-1 HSRL system. This method has retrieved the aerosol depolarization ratio, backscatter coefficient, extinction coefficient, and optical depth. For validation purposes, we compared retrieved results with those obtained through CALIPSO. The results have shown a continuous profile alignment between the two datasets, with DQ-1 describing an improved signal-to-noise ratio of approximately 10 dB. Optical property profiles from NASA Micro Pulse Lidar NETwork (MPLNET) stations were selected for validation with the DQ-1 measurements, resulting in a relative error of 25%. Between June 2022 and December 2022, aerosol optical depth measurements using the DQ-1 satellite and the AErosol RObotic NETwork (AERONET) were correlated and yielded a value of R2 0.803. We use the DQ-1 dataset to initially investigate the transport processes of the Saharan dust and the South Atlantic volcanic ash. These validations and applications show that the DQ-1 HSRL system can accurately measure global aerosols and holds significant prospects for earth science applications. [ABSTRACT FROM AUTHOR]

The new-generation atmospheric environment monitoring satellite DQ-1, launched successfully in April 2022 carries the Aerosol and Carbon Detection Lidar (ACDL) which is capable of globally profiling the aerosols and clouds optical properties with high accuracy. The ACDL/DQ-1 is a high-spectral-resolution lidar (HSRL) with two-wavelength polarization detection, that can be utilized to derive the aerosol optical properties. The methods are specifically developed for the data processing and optical properties retrieval according to the specific characteristics of the ACDL system are introduced in detail in this paper. Considering the different signal characteristics and different background noise behaviours of each channel during daytime and nighttime, the procedures of data pre-processing, denoising process and quality control are applied to the original measurement signals. The aerosol and cloud optical properties products of the ACDL/DQ-1 including total depolarization ratio, backscatter coefficient, extinction coefficient, lidar ratio and colour ratio can be calculated by the retrieval algorithms presented in this paper. Two measurement cases with use of the ACDL/DQ-1 on 27th June 2022 and the global averaged aerosol optical depth (AOD) from 1st June to 4th August 2022 are provided and analysed, which demonstrated the measurement capability of the ACDL/DQ-1. [ABSTRACT FROM AUTHOR]