Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

Transponder-type laser interferometer prototype for spaceborne gravitational wave detectors.

Transponder-type laser interferometry is essential in spaceborne gravitational wave detection missions. This paper presents a transponder-type laser interferometer prototype for potential noise calibration of spaceborne gravitational wave detectors. Using a digital optical phase-locked loop, we successfully locked the phase of the slave laser to the master laser (∼200p W). Once the link between the master laser and the slave laser is established, the two satellites (essentially two lasers) form a transponder-type laser interferometer. We carefully analyze the measurement stability and noise characteristics of the interferometer, and the results show that the Allan deviation of the zero drift can reach 243.2 pm at t=0.429s, while the noise spectral density has a typical 1/f line shape with a floor of 21p m/H z 1/2 at 1 Hz. The coherence analysis shows that the temperature drift is an important factor limiting the performance of the interferometer below 2 mHz, while the frequency noise of the master laser is not dominant in the experiment. Transponder-type laser interferometers have a wide range of applications in intersatellite communication and measurement. Our design can serve as a valuable reference for gravitational wave detection missions such as LISA.

Successful treatment of infantile refractory bullous pemphigoid with baricitinib.

Infantile bullous pemphigoid (BP) is a rare autoantibody-mediated skin disorder. We report the effective treatment of a 6-month-old infant with BP using baricitinib, a Janus kinase (JAK) inhibitor, after failure with steroids and intravenous immunoglobulin. The patient achieved full remission and discontinued all medications without any relapses. To our knowledge, this is the first case of baricitinib used in an infant with BP.

A Novel Biosensor for the Detection of Glucose Concentration Using the Dual-Peak Long Period Grating in the Near- to Mid-Infrared.

In this article, we demonstrate an improved efficient fibre sensor with a high sensitivity to measure glucose concentrations in the physiological range of human beings, operating in a broad spectral bandwidth from the near- to mid-infrared. The sensor consists of a dual-peak long period grating (DPLPG) with a period of 150 µm inscribed in an optical fibre with a diameter of 80 µm. The investigation of sensing for refractive index results in a sensitivity of ~-885.7 nm/refractive index unit (RIU) and ~2008.6 nm/RIU in the range of 1.30-1.44. The glucose measurement is achieved by the immobilisation of a layer of enzyme of glucose oxidase (GOD) onto the fibre surface for the selective enhancement of sensitivity for glucose. The sensor can measure glucose concentrations with a maximum sensitivity of -36.25 nm/(mg/mL) in the range of 0.1-3.0 mg/mL. To the best of our knowledge, this is the highest sensitivity ever achieved for a measurement of glucose with a long period grating-based sensor, indicating its potential for many applications including pharmaceutical, biomedical and food industries.

Ultrasensitive Screening of Endocrine-Disrupting Chemicals Using a Surface Plasmon Resonance Biosensor with Polarization-Compensated Laser Heterodyne Feedback.

Developing an ultrasensitive and reliable device for continuous monitoring of various endocrine-disrupting chemicals (EDCs) is in high demand, yet it remains a significant challenge. Traditional label-free surface plasmon resonance (SPR) sensing relies on the interaction of the surface plasmon wave and the sensing liquid via intensity modulation, endowed with simple structure and easy-to-miniaturization, however suffering from inferior sensitivity and stability. Here, we propose a novel optical structure in which the frequency-shifted light of different polarization returned to the laser cavity to stimulate laser heterodyne feedback interferometry (LHFI), hence amplifying the reflectivity change caused by the refractive index (RI) variations on the gold-coated SPR chip surface, and the s-polarized light could be further used as a reference to compensate for the noise of the LHFI-amplified SPR system, resulting in nearly three orders of magnitude enhancement of the RI sensing resolution (5.9 × 10-8 RIU) compared to the original SPR system (2.0 × 10-5 RIU). To further boost intense signal enhancement, custom-designed gold nanorods (AuNRs), which were optimized by the finite-difference time-domain (FDTD) simulation, were used to generate localized surface plasmon resonance (LSPR). By exploiting the estrogen receptor as the recognition material, estrogenic active chemicals were detected with a 17ß-estradiol/L detection limit of 0.004 ng, which is nearly 180-fold lower than that of the system without introducing AuNRs. The developed SPR biosensor is expected to be capable of screening various EDCs with universality by using several nuclear receptors, such as the androgen receptor and thyroid receptor, and will substantially accelerate the assessment of global EDCs.

An Ultrasensitive and Universal Surface Plasmonic Biosensor for Detection of Micropollutants in Aquatic Environments.

Simple yet ultrasensitive and accurate quantification of a variety of analytical targets by virtue of a universal sensing device holds promise to revolutionize environmental monitoring, medical diagnostics, and food safety. Here, we propose a novel optical surface plasmon resonance (SPR) system in which the frequency-shifted light of different polarizations returned the laser cavity to stimulate laser heterodyne feedback interferometry (LHFI), hence amplifying the reflectivity change caused by the refractive index (RI) variations on the gold-coated SPR chip surface. In addition, the s-polarized light was further used as the reference to compensate the noise of the LHFI-amplified SPR system, resulting in nearly 3 orders of magnitude enhancement of RI resolution (5.9 × 10-8 RIU) over the original SPR system (2.0 × 10-5 RIU). By exploiting nucleic acids, antibodies, and receptors as recognition materials, a variety of micropollutants were detected with ultralow detection limits, ranging from a toxic metal ion (Hg2+, 70 ng/L) to a group of commonly occurring biotoxin (microcystins, 3.9 ng microcystin-LR/L) and a class of environmental endocrine disruptors (estrogens, 0.7 ng 17ß-estradiol/L). This sensing platform exhibits several distinct characteristics, including dual improvement of sensitivity and stability and common-path optical construction without needing optical alignment, demonstrating a promising avenue toward environmental monitoring.

Method for a deflection-type refractometer measuring the fringe shift by using linear Fresnel zone plates.

This study describes the design and performance of a deflection-type refractometer based on measuring the fringe shift from the Fresnel diffraction pattern to solve some major limitations of conventional differential refractometers, such as measurement range, resolution, zero balancing, and monitoring analysis. The refractometer apparatus comprises a coherent light source, linear Fresnel zone plate, measuring cell, and image capture device mounted on a movable platform. The distance measurement unit is configured to detect fringe deflection due to the difference in refractive index between the sample and the reference. To achieve this, distance measurements with an accuracy of a few nanometers by using the local frequency method and fringe shift measurement method are quite feasible. The uncertainty in this technique is determined by the smallest change in the longitudinal displacement of the image for which the CCD camera can detect a change in pixel position. The refractive index is obtained with a highly extended measurement range of at least ±0.4R I U and precision of the order of 2×10-4 R I U. A numerical comparison between computer simulation of the diffraction patterns that occur when the linear Fresnel zone plate is illuminated by a plane light traveling parallel to the z axis.

High-precision digital optical phase locking for 10-12 W order weak light for a spaceborne gravitational wave interferometer.

We developed a digital optical phase-locking loop (DOPLL) for weak light phase locking in spaceborne gravitational wave interferometers (SGWIs). Using the system, we successfully locked the phase of the slave laser to the master laser with the power of only several picowatts, much smaller than the LISA requirement (100 pW). The system does not introduce steady-state errors, and the Bode diagram shows its stability. The out-loop phase noise floor (2.3×10-4 and 5.2×10-4 r a d/H z 1/2) is very close to the shot noise limit. The Allan standard deviation of the heterodyne signal reaches 3.1×10-17 at 1000 s. With the previous automatic locking program designed by other researchers, the results demonstrate that DOPLLs have bright application prospects and can be applied in the transducer of the SGWI.

Improved opposition-based self-adaptive differential evolution algorithm for vibrational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering thermometry.

We propose an improved opposition-based self-adaptive differential evolution (IOSaDE) algorithm for multi-parameter optimization in vibrational hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (CARS) thermometry. This new algorithm self-adaptively combines the advantages of three mutation schemes and introduces two opposite population stages to avoid premature convergence. The probability of choosing each mutation scheme will be updated based on its previous performance after the first learning period. The IOSaDE method is compared with nine other traditional differential evolution (DE) methods in simulated spectra with different simulation parameters and experimental spectra at different probe time delays. In simulated spectra, both the average and standard deviation values of the final residuals from 20 consecutive trials using IOSaDE are more than two orders of magnitude smaller than those using other methods. Meanwhile, the fitting temperatures in simulated spectra using IOSaDE are all consistent with the target temperatures. In experimental spectra, the standard deviations of the fitting temperatures from 20 consecutive trials decrease more than four times by using IOSaDE, and the errors of the fitting temperatures also decrease more than 18%. The performance of the IOSaDE algorithm shows the ability to achieve accurate and stable temperature measurement in CARS thermometry and indicates the potential in applications where multiple parameters need to be considered.

Transcranial Doppler Ultrasound for Monitoring the Cerebral Hemodynamic Changes and Prognosticating Outcomes in Venoarterial Extracorporeal Membrane-Oxygenated Patients.

Objective: Patients receiving venoarterial extracorporeal membrane oxygenation (VA-ECMO) support may have cerebral hemodynamic changes whose impact on patient outcome are not fully elucidated. This study aims to evaluate the correlation between cerebral hemodynamic changes and prognostic outcome in patients during VA-ECMO. Methods: Transcranial Doppler (TCD) ultrasound examination was performed to attain the systolic velocity (Vs), diastolic velocity (Vd), mean velocity (Vm), and pulsatility index (PI) of patients undergoing VA-ECMO. Cardiac ultrasound was also performed to assess the correlation between the left ventricular outflow tract velocity time integral (LVOT VTI), left ventricular ejection fraction (LVEF), and middle cerebral artery (MCA) with the systolic peak. Moreover, we assessed the predictive value of LVOT VTI and LVEF in patients with the systolic peak. Patients were divided into survival and death groups according to the 28-day survival period. Clinical data were compared between the two groups to investigate the effects of cerebral hemodynamic changes on the prognosis of VA-ECMO patients. Results: We found that the patient's LVOT VTI and LVEF had high predictive values for the systolic peak of the right middle cerebral artery. The initial LVEF, Vs, Vd and PI, and lactate level as well as the MODS incidence rate difference were significantly different between the survival and death groups. In addition, the results showed that the initial Vs value was an independent risk factor for the prognosis of patients undergoing VA-ECMO. Conclusions: Cerebral hemodynamic changes may occur in patients supported by VA-ECMO. In addition, a poor cerebral arterial pulsatile blood flow was closely correlated with an unfavorable outcome in these patients.

All-fiber laser feedback interferometry with 300 m transmission distance.

A novel, to the best of our knowledge, interferometry based on the laser feedback technique with long transmission distance is proposed. The system has the advantages of high sensitivity for uncooperative targets and a simple structure. Also, the quasi-common path orthogonally polarized light compensation method is designed to compensate for the drift in long-distance transmission and achieves more than 200 times reduction experimentally. Using a copper block as a target, the displacement resolution of 20 nm is demonstrated experimentally with 300 m transmission distance. The sub-microwatt power consumption of the measurement beam indicates the high sensitivity of the interferometry. The performance, in terms of linearity, is also evaluated. Although a lot needs to be improved, the proposed method is promising for further development toward practical applications, like sensors in remote, nuclear radiative, or other harsh conditions.

Analysis of phase response of fiber Fabry-Pérot cavity microphones.

In this paper, the phase response of fiber Fabry-Pérot cavity-based fiber optic microphones (FFPC-FOMs) is discussed through an analysis of the results of simulation and experiments. The phase difference of FFPC-FOMs mainly originates from two aspects: different phase lags of the mechanical-acoustic systems and different quadrature working points (Q*) on interference curves. The former is analyzed by an impedance-type analogous circuit, and the simulation results reveal that the change in cavity length and resonance frequency in a large range have an insignificant influence on the phase difference. The latter shows a unique effect on the phase difference and causes the phase of FFPC-FOMs to be either in or out of phase. The phase differences of four samples of FFPC-FOMs with different cavity lengths and resonance frequencies are measured in the frequency range 50 Hz-4 kHz. Experimental results of the phase difference are well consistent with simulation results. All samples of FFPC-FOMs can be divided into two groups: one is near 0° and the other is near 180°. In addition, the FFPC-FOMs in each group have good phase consistency for the array applications.

Ultrasound-modulated laser feedback tomography in the reflective mode.

A novel method of ultrasound-modulated optical tomography (UOT) detection based on the laser feedback technology is proposed in this Letter. The system has advantages such as a simple structure, high sensitivity, and reflective configuration. Effective penetration depths of up to 9 cm and 5 cm in phantom and biological tissues, respectively, have been demonstrated experimentally. The detection capability is comparable with the state of the art in the transmission mode but with a much lower photon consumption. Although a lot remains to be improved, the proposed method is promising for further development toward practical applications.

Ultrasound modulated laser confocal feedback imaging inside turbid media.

Ultrasound modulated laser confocal feedback technology is proposed in the imaging inside turbid media. By selecting the detectable signal photons and rejecting the background noise photons in the frequency domain based on the ultrasound modulation, the signal-to-noise ratio (SNR) can be much improved, especially in the turbid media, compared with the traditional imaging without ultrasound modulation. This is a promising method to reach both a larger penetration depth and a better SNR than other optical methods.

Depth of focus extension by filtering in the frequency domain in laser frequency-shifted feedback imaging.

The depth of focus extension in optical imaging is of considerable interest. In this paper, a laser frequency-shifted feedback scanning imaging configuration is demonstrated whose depth of focus is greatly extended through numerical filtering. The transmission characteristics of the system are studied. The original image is acquired through a two-dimensional scanning point by point with the target placed on a defocused plane. Filtered in the frequency domain, images on any oriented plane can be refocused. The superior performances are presented by imaging a three-dimensional target, and the process of gradual refocusing is demonstrated. To obtain the maximum extension in the depth of defocus, a series of numerical experiments has been carried out, which reveals its depth of focus is capable of being extended to four times the length of the objective focus length. The fabulous performances can motivate three-dimensional surface profile measurement.

Spin Rate Effects in a Micromachined Electrostatically Suspended Gyroscope.

Spin rate of a high-speed spinning-rotor gyroscope will make a significant impact on angular rate sensor performances such as the scale factor, resolution, measurement range, and bias stability. This paper presents the spin rate effects on performance indicators of a microelectromechanical systems (MEMS) gyroscope where a free-spinning rotor is electrostatically suspended in an evacuated vacuum cavity and functions as a dual-axis angular rate sensor. Theoretical models of the scale factor and measurement range of such a spinning-rotor gyroscope are derived. The experimental results indicate that the measured scale factors at different settings of the spin rate match well with the theoretical predication. In order to separate the disturbance component of the rotation control loop on the gyroscope output, a testing strategy is proposed by operating the gyroscope at different spin rates. Experimental results on a prototype gyroscope show that the squared drive voltage generated by the rotation control loop is approximately proportional to the noise of the gyroscope output. It was further investigated that an improved performance of such spinning-rotor gyroscopes can be achieved by operating the gyroscope rotor at an optimal spin rate.

Laser diode side-pumped Nd:YVO4 microchip laser with film-etched microcavity mirrors.

Microchip lasers are applied as the light sources on various occasions with the end-pumping scheme. However, the vibration, the temperature drift, or the mechanical deformation of the pumping light in laser diodes in the end-pumping scheme will lead to instability in the microchip laser output, which causes errors and malfunctioning in the optic systems. In this paper, the side-pumping scheme is applied for improving the disturbance-resisting ability of the microchip laser. The transverse mode and the frequency purity of the laser output are tested. To ensure unicity in the frequency of the laser output, numerical simulations based on Fresnel-Kirchhoff diffraction theory are conducted on the parameters of the microchip laser cavity. Film-etching technique is applied to restrain the area of the film and form the microcavity mirrors. The laser output with microcavity mirrors is ensured to be in single frequency and with good beam quality, which is significant in the applications of microchip lasers as the light sources in optical systems.

Fiber self-mixing interferometer with orthogonally polarized light compensation.

A fiber heterodyne self-mixing interferometer with orthogonally polarized light compensation is achieved. This system can adapt to various complex scenes while still keeping ultra-high sensitivity and anti-disturbance capability. Ultra-high sensitivity microchip laser is used as the laser source and polarization maintaining(PM) fiber makes the light path easy to accommodate to complex spaces, such as remote or narrow and small space. Besides, orthogonally polarized light inside PM fiber can eliminate the measurement error on account of environment disturbance. At present, the displacement resolution could be less than 10nm, which shows a great potential in nano-metrology.

Common-path heterodyne self-mixing interferometry with polarization and frequency multiplexing.

A heterodyne Nd:YVO4 microchip laser self-mixing interferometry based on frequency and polarization multiplexing has been demonstrated. By using two orthogonally polarized lights to measure the measurement and reference target, the effect of the acousto-optic crystal thermal creep and air disturbance in interference light path is eliminated. In addition, the measurement error caused by the difference between two identical microchip lasers is compensated for by shifted frequency multiplexing technique. A rate equations model with multi-channel frequency-shifted feedback is established for interpreting the principle of the interferometry. Due to the ultrahigh sensitivity of the microchip laser, the target used in the experiment is a non-cooperative object which is different from the targets in conventional Michelson interferometers. Under typical room conditions, the short-term resolution is better than 2.5 nm, and the long-term zero drift is less than 60 nm within 7 h. The result shows that this self-mixing interferometry system is feasible and robust in the field of displacement measurement.