Time sequence variation of incoherent and coherent random laser based on positive replica of abalone shell.

Besides the scattering structures, the energy transfer (ET) process in the gain medium plays a significant role in the competition between coherent (comprising strongly coherent components) and incoherent (consisting of weakly coherent or "hidden" coherent components) modes of random lasers. In this study, bichromatic emission random lasers were successfully created using polydimethylsiloxane (PDMS) replicas with grooved structures that imitate the inner surface of abalone shells as scattering substrates. The influence mechanism of the ET process from the monomer to dimer in the Rhodamine 640 dye on the competition of random laser modes was thoroughly investigated from both spectral and temporal dimensions. It was confirmed that the ET process can reduce the gain of monomers while amplifying the gain of dimers. By considering the dominant high-efficiency ET processes, an energy transfer factor associated with the pump energy density was determined. Notably, for the first time, it was validated that the statistical distribution characteristics of the time sequence variations in the coherent random laser generated by dimers closely resemble a normal distribution. This finding demonstrates the feasibility of producing high-quality random number sequences.

Pretreatment of membrane dye wastewater by CoFe-LDH-activated peroxymonosulfate: Performance, degradation pathway, and mechanism.

When a membrane is used to treat dye wastewater, dye molecules are continually concentrated at the membrane surface over time, resulting in a dramatic decrease in membrane flux. Aside from routine membrane cleaning, the pretreatment of dye wastewater to degrade organic pollutants into tiny molecules is a facile solution to the problem. In this study, the use of layered double hydroxide (LDH) to activate peroxymonosulfate (PMS) for efficient degradation of organic pollutant has been thoroughly investigated. We utilized a simple two-drop co-precipitation process to prepare CoFe-LDH. The transition metal components in CoFe-LDH effectively activate PMS to create oxidative free radicals, and the layered structure of LDH increases the number of active sites, and thereby considerably enhancing the reaction rate. It was found that the reaction process produced non-free and free radicals, including singlet oxygen (1O2), sulfate radicals (SO4•-), and hydroxyl radicals (•OH), with 1O2 being the dominant reactive species. Under the optimal conditions (pH 6.7, PMS dosage 0.2 g/L, catalyst loading 0.1 g/L), the degradation of Acid Red 27 dye in the CoFe-LDH/PMS system reached 96.7% within 15 min at an initial concentration of 200 mg/L. The CoFe-LDH/PMS system also exhibited strong resistance to inorganic ions and pH during the degradation of organic pollutants. This study presents a novel strategy for the synergistic treatment of dye wastewater with free and non-free radicals produced by LDH-activated PMS in a natural environment.

Electrocatalytic Degradation of Levofloxacin, a Typical Antibiotic in Hospital Wastewater.

Presently, in the context of the novel coronavirus pneumonia epidemic, several antibiotics are overused in hospitals, causing heavy pressure on the hospital's wastewater treatment process. Therefore, developing stable, safe, and efficient hospital wastewater treatment equipment is crucial. Herein, a bench-scale electrooxidation equipment for hospital wastewater was used to evaluate the removal effect of the main antibiotic levofloxacin (LVX) in hospital wastewater using response surface methodology (RSM). During the degradation process, the influence of the following five factors on total organic carbon (TOC) removal was discussed and the best reaction condition was obtained: current density, initial pH, flow rate, chloride ion concentration, and reaction time of 39.6 A/m2, 6.5, 50 mL/min, 4‱, and 120 min, respectively. The TOC removal could reach 41% after a reaction time of 120 min, which was consistent with the result predicted by the response surface (40.48%). Moreover, the morphology and properties of the electrode were analyzed. The degradation pathway of LVX was analyzed using high-performance liquid chromatography-mass spectrometry (LC-MS). Subsequently, the bench-scale electrooxidation equipment was changed into onboard-scale electrooxidation equipment, and the onboard-scale equipment was promoted to several hospitals in Dalian.

Strain-insensitive temperature sensing with a dual polarization fiber grating laser.

In this paper, a strain-insensitive temperature sensor based on a dual polarization fiber grating laser is demonstrated. The laser is fabricated by inscribing two wavelength-matched Bragg gratings in an Er-doped fiber. It emits single-longitudinal-mode output in wavelength domain and generates a RF-domain signal as a beat note between the two polarization modes. A temperature sensor has been exploited by monitoring the beat frequency. The measured temperature sensitivity is -78.46 kHz/°C. Theoretical analysis suggests that the temperature response is a result of both the differences in thermo-optic coefficient and thermal expansion between the core and cladding. In contrast, the sensor is almost insensitive to applied axial strain. We found that the strain insensitivity is due to the compensation between the strain-induced birefringence change and the effect of the elongation/material index change. The proposed sensor can be applied for reliable and precise measurement of temperature independently, towards the applications in structural integrity, oil-well monitoring, aerospace engineering, and process control.

Multi-octave tunable RF signal generation based on a dual-polarization fiber grating laser.

A simple technique has been proposed and demonstrated to generate radio-frequency (RF) signal based on a fiber grating laser with multi-octave tunablity. The laser is fabricated by inscribing a wavelength-matched Bragg grating pair in a short section of low-birefringence Er/Yb co-doped fiber. A RF signal can be obtained by beating the two-polarization mode output with its frequency determined by the birefringence within the cavity. By slicing the laser cavity into two sections and then aligning them with a rotated angle, the output beat frequency can be continuously tuned in a multi-octave frequency range as shown in the experiment from 2.05 GHz down to 289 MHz, as a result of the induced change in optical length for each polarization mode. The present technique has the advantages including simple scheme and large tuning range, and the ability of tuning could be further improved by use of active fibers with higher birefringence.

Simultaneous strain and temperature fiber grating laser sensor based on radio-frequency measurement.

We propose and experimentally demonstrate a novel simultaneous strain and temperature fiber optic sensor. The sensing head is formed by two concatenated ultra-short distributed Bragg reflector lasers that operate in single longitude mode with two polarization modes. The total length of the sensing head is only 18 mm. The two lasers generate two polarization mode beat notes in the radio-frequency range which show different frequency response to strain and temperature. Simultaneous strain and temperature measurement can be achieved by radio-frequency measurement. This approach has distinctive advantages of ease of interrogation and avoidance of expensive wavelength detection.

193 nm excimer laser inscribed Bragg gratings in microfibers for refractive index sensing.

We demonstrate the inscription of fiber Bragg gratings by 193 nm ArF excimer laser in microfibers drawn from the standard single mode telecommunication fiber. Fiber Bragg gratings are directly inscribed in a series of microfibers with diameter ranged from tens of µm to 3.3 µm without hydrogen loading or other treatment to photosensitize the microfibers. Four reflection peaks are observed where three correspond to high order mode resonances. The resonance wavelength depends on the fiber diameter and it sharply blueshifts as the diameter is decreased below 10 µm. The gratings are characterized for their response to ambient refractive index. The higher order mode resonance exhibits higher sensitivity to refractive index.

Beat frequency trimming of dual-polarization fiber grating lasers for multiplexed sensor applications.

We demonstrated a method to trim the beat frequency of dual-polarization fiber grating lasers by side-exposing the laser cavity to UV beam. The UV-side-illumination induces an additional birefringence of the cavity fiber and therefore permanently changes the beat frequency of the laser. The beat frequency can be trimmed up or trimmed down, depending on the UV incident direction relative to the intrinsic polarization axis of the active fiber. A trimming range as much as ~700MHz has been achieved. This method allows us to actively control the beat frequency of dual-polarization fiber grating lasers. A 6-channel RF-frequency division multiplexed polarimetric fiber grating laser array has been demonstrated.

Dual polarization fiber grating laser hydrophone.

A novel fiber optic hydrophone based on the integration of a dual polarization fiber grating laser and an elastic diaphragm is proposed and experimentally demonstrated. The diaphragm transforms the acoustic pressure into transversal force acting on the laser cavity which changes the fiber birefringence and therefore the beat frequency between the two polarization lines. The proposed hydrophone has advantages of ease of interrogation, absolute frequency encoding, and capability to multiplex a number of sensors on a single fiber by use of frequency division multiplexing technique.