Search

The longitudinal relaxation time (T 1 ) of noble gas nuclear spins is a critical parameter for evaluating the performance of an atomic comagnetometer, significantly influencing the signal-to-noise ratio of the system. Traditional measurement techniques, such as the free induction decay method combined with the spin growth technique (FIDSG), are time-consuming for gases with extended T 1 durations, such as 21 Ne, and are prone to substantial environmental variability. Here, we propose the transverse low-frequency square-wave magnetic field modulation (LSMM) method for the rapid measurement of T 1 . The experiment indicates that the LSMM significantly condenses the measurement time to 19.2% of the original, thereby diminishing the robustness demands of the system. Although a minor discrepancy of up to 3 min (or 1.3%) exists between LSMM and FIDSG results, the LSMM method provides strong support for calibrating the performance of comagnetometer cells and conducting various nuclear spin polarization experiments, thereby improving efficiency and reducing energy loss.

We report a method to enhance the sensitivity of coherent population trapping (CPT) magnetometers using a combination of left-handed and right-handed circularly polarized light phase-delay detection and a differential detection scheme. The approach can achieve a four third-fold enhancement of the CPT dispersion signal slope and a three-fold reduction in noises. The proposed method experimentally exhibits a four third-fold magnetic field resolution enhancement in CPT open-loop measurements, and the differential method could achieve a sensitivity of 1  p T / H z at 10 Hz and a sensitivity of 0.4  p T / H z at 50-100 Hz in the CPT closed-loop measurement, which is a four-fold sensitivity enhancement compared to the single-transmitted CPT magnetometer.

The coupling of electron spin and nuclear spin through spin-exchange collisions compensates for external magnetic field interference in the spin-exchange relaxation-free (SERF) comagnetometer. However, the compensation ability for magnetic field interference along the detection axis is limited due to the presence of nuclear spin relaxation. This paper aims to enhance the self-compensation capability of the system by optimizing the pressure of the noble gas during cell filling. Models are established to describe the relationships between the nuclear spin polarization, the polarizing magnetic field of nuclei, the magnetic field suppression factors, and the pressure of the noble gas in the K-Rb- 21 Ne atomic ensemble. Experiments are conducted using five cells with different pressure. The results indicate that in the positive pressure area, the nuclear spin polarization decreases while the equivalent magnetic field experienced by the noble gas increases with increasing pressure. The magnetic field suppression factor for transverse fields increases as the pressure increases, leading to a decrease in the ability to suppress low-frequency magnetic field interference. Moreover, at the cell temperature of 180°C and a transverse residual field gradient of 4.012 nT/cm, the system exhibits its strongest capability to suppress transverse magnetic field interference when the pressure of 21 Ne is around 0.7 atm.

The single-beam comagnetometer working in the spin-exchange relaxation-free (SERF) state is being developed into a miniaturized atomic sensor with extremely high precision in rotation measurement. In this paper, we propose a reflective configuration for the single-beam SERF comagnetometer. The laser light simultaneously used for optical pumping and signal extraction is designed to pass through the atomic ensemble twice. In the optical system, we propose a structure composed of a polarizing beam splitter and a quarter-wave plate. With this, the reflected light beam can be separated entirely from the forward propagating one and realize a complete light collection with a photodiode, making the least light power loss. In our reflective scheme, the length of interaction between light and atoms is extended, and because the power of the DC light component is attenuated, the photodiode can work in a more sensitive range and has a better photoelectric conversion coefficient. Compared with the single-pass scheme, our reflective configuration has a stronger output signal and performs better signal-to-noise ratio and rotation sensitivity. Our work has an important impact on developing miniaturized atomic sensors for rotation measurement in the future.

The high-precision and portable nonlinear magneto-optical rotation (NMOR) atomic magnetometer has significant potential in the direction of magnetic field measurement under a geomagnetic environment. Here, we propose a single-beam NMOR atomic magnetometer with amplitude modulation based on a fiberized electro-optic modulator (EOM) for the first time, to the best of our knowledge, which provides a feasible scheme for the integrated design. A theoretical model of the system response signal as a function of the modulation amplitude is established by a Jones matrix. Based on the theoretical model, the influence mechanism of the modulation amplitude on the system response signal is further analyzed and the optimal modulation parameters can be determined. Finally, a sensitivity of 42.67 fT/Hz 1/2 at 50-µT magnetic field is achieved. The proposed scheme is also applicable to other magnetometers under a geomagnetic environment.

The cell temperature working point optimization of the spin-exchange relaxation-free (SERF) co-magnetometer is studied theoretically and experimentally in this article. Based on the steady-state solution of the Bloch equations, the steady-state response model of the K-Rb- 21 Ne SERF co-magnetometer output signal with cell temperature is established in this paper. And combined with the model, a method to find the optimal working point of the cell temperature that incorporates the pump laser intensity is proposed. The scale factor of the co-magnetometer under different pump laser intensities and cell temperatures is obtained experimentally, and the long-term stability of the co-magnetometer at the different cell temperatures with corresponding pump laser intensities is measured. The results show that the bias instability of the co-magnetometer is reduced from 0.0311 deg/h to 0.0169 deg/h by obtaining the optimal working point of the cell temperature, which verifies the validity and accuracy of the theoretical derivation and the proposed method.

The magnetic field gradient affects the improvement of sensitivity and magnetic field suppression ability of the spin-exchange relaxation-free co-magnetometer. This paper proposes a response model of a co-magnetometer considering magnetic field gradient based on state-space method. The effects of transverse and longitudinal magnetic field gradients on the system's scale factor, bandwidth and magnetic field response are analyzed. The analysis shows that transverse gradient affects the whole frequency band of system response, including steady-state and dynamic performance, while longitudinal gradient only affects steady-state response. With the increase of the gradient, the effect becomes more significant. The test results are in agreement with the theory, proving the accuracy of the theoretical analysis. The rotational sensitivity at 1 Hz decreases from 6.51 ×10 -6 °/s/Hz 1/2 to 5.05×10 -5 °/s/Hz 1/2 in the presence of a magnetic field gradient of -40 nT/cm, so the effect of the magnetic field gradient is critical. This work provides an accurate model for evaluating the effects of magnetic field gradients and provides a method for suppressing gradients using gradient coils, which are important for improving the sensitivity and accuracy of co-magnetometers.

A new method for the detection of atomic spin precession based on the Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated. Different from the conventional polarization detection methods which obtain the atomic spin precession signal by measuring the change of the probe laser power, the proposed method uses the laser modulated by an electro-optic phase modulator (EOM) as the source of the interferometer, and obtains the atomic spin precession signal by measuring the phase difference between the two arms of the MZI. The output of interferometer is independent of the probe laser power, which avoids the system error caused by the fluctuation of the probe laser power, and the long-term stability of the system is effectively improved. At the same time, the method adopts high-frequency electro-optic modulation, which can effectively suppress low-frequency noise, such as 1/f noise, and can significantly improve the detection sensitivity. The rotation sensitivity and long-term stability of the atomic comagnetometer were tested using the MZI detection method and a typical detection method, respectively. The comparison results show that the proposed method has the highest low frequency sensitivity and the potential to improve the long-term stability of the system.

Rb optically pumped magnetometer (OPM) based on electron paramagnetic resonance (EPR) show advantages to measure the nuclear magnetization and have succeeded in fundamental physics and rotation sensing, etc. The magnetometry sensitivity is a key performance of these Rb OPMs which should be improved. In this study, a high sensitivity Rb OPM is demonstrated theoretically and experimentally. To improve the sensitivity, acousto-optic modulation based on balanced detection is applied to suppress the probe noises. Compared with the conventional optical rotation detection for this OPM configuration, the probe noise shows a significant suppression especially in low frequencies. Eventually, a simultaneous dual-axis transverse measurement with 30 fT/Hz 1/2 sensitivity is achieved in a 200 Hz bandwidth and a 250nT linear working range. In addition, we utilize a closed-loop feedback to improve the stability and enlarge the transverse measurement range to 10µT order of magnitude while maintain the open-loop performances. A quasi-static magnetic field measurement can also be achieved in the longitudinal direction in the closed-loop mode. This OPM can serve for the nuclear magnetization measurement with a high sensitivity especially in environments with a large magnitude of the external magnetic field.

In this paper, the effect of longitudinal electron spin polarization under the combined action of alkali metal density ratio and pump laser power density on the hybrid optically pumped co-magnetometer operated in the spin-exchange relaxation-free (SERF) regime is studied. The AC response model of rotation velocity and magnetic noise of the SERF co-magnetometer system is proposed, and the factors of frequency and system bandwidth are considered. Based on the proposed response model, the error equation of the system is obtained, and the relationship between alkali metal density ratio and pump laser power density and the system noise response is theoretically analyzed and experimentally tested. The results show that when the product of pumping rate and alkali metal density ratio is greater than the electron spin relaxation rate, there is a longitudinal electron spin polarization point that minimizes the system error. In addition, the range of minimum error calculated results obtained by changing the pumping rate for the cells with different alkali metal density ratios is within 5% of the average value, that is, their minimum error potential is roughly the same within a certain range. Under the experimental conditions in this paper, due to the limitation of the electron spin relaxation rate and the operating capacity of the pump laser, the optimal alkali metal density ratio range is about 1/100-1/300.

We have developed a single-beam spin-exchange relaxation-free comagnetometer using elliptically polarized light for dual-axis rotation measurement. The light beam propagating through the glass cell is simultaneously used for optical pumping and signal extraction. Combined with transverse magnetic field modulation, the rotation information can be collected through a balanced polarimeter module and a lock-in amplifier. Also, we propose a decoupling method by adjusting the phase shift of the reference signal, allowing the device to realize biaxial signal decoupling while still maintaining its self-compensation state. Compared to those without decoupling, our method improves the performance of our device in its signal-to-noise ratio and rotation sensitivity. The single-beam comagnetometer scheme and the decoupling method have a positive impact on the development of miniaturized atomic sensors for high-precision inertial measurement.

We investigate the magnetic pulse response of the optically pumped comagnetometer operated in the spin-exchange relaxation-free (SERF) regime. The pulse response model describing the evolution of the coupled spin ensemble of alkali metal and noble gas during and after the pulse is established for the first time. A three-beam comagnetometer is created with a circularly and two linearly polarized lasers to detect the responses in the three axes of the comagnetometer simultaneously and independently. The results indicate that the response to the small pulse excitation is dominated by the electron spins, while the response to the large pulse excitation and both responses after the pulse excitation consist of a fast and a slow oscillation, which are dominated by the electron spins and nuclear spins, respectively. We also observe novel dynamics of the coupled spin ensemble when the nuclear spins are tipped far away from equilibrium. The theory and method presented here can not only facilitate the investigation on the dynamics of the optically pumped coupled spin ensemble, but also shed light on the application of the pulse modulation technology in the SERF comagnetometer.

We present theoretically obtained photoelectron momentum distributions (PMDs) for the strong field ionization of argon in an elliptically polarized laser field at a central wavelength of 400 nm. Three different theoretical approaches, namely, a numerical solution of the time-dependent Schrödinger equation (TDSE), a nonadiabatic model, and a classical-trajectory Monte Carlo (CTMC) model are adopted in our calculations. From the TDSE calculations, it is found that the attoclock offset angle (most probable electron emission angles with respect to the minor axis of the laser's polarization ellipse) in the PMD increases with rising ATI order. While this result cannot be reproduced by the CTMC model, the nonadiabatic model achieves good agreement with the TDSE result. Analysis shows that the nonadiabatic corrections of the photoelectron initial momentum distribution (in both longitudinal and transverse directions with respect to the tunneling direction) and nonadiabatic correction of the tunneling exit are responsible for the ATI order-dependent angular shift.

The misalignment error of the pumping laser in the atomic comagnetometer (ACM) dramatically diminishes the efficiency of the optical pumping process (characterized by the polarization of the hybrid atomic spin ensembles containing electron spins and nuclear spins) and deteriorates the performance of the ACM (characterized by the Allan standard deviation). In this work, a steady-state response model considering the misalignment error of the pumping laser is established and an in-situ evaluation method for this error is proposed. Based on the evaluation method, the influence of this misalignment error on the pumping efficiency and the performance of the ACM is quantitatively analyzed. Furthermore, a pumping laser alignment method based on the second harmonic of a single-beam magnetometer is then proposed, whose effectiveness is verified by experiments. The experimental results show that compared to the original ACM with the severely misaligned pumping laser, the polarization of the hybrid atomic spin ensembles of the ACM with the pumping laser aligned by the proposed method is increased by about 19%, and the corresponding Allan variance at 100s is reduced by about 40%.

Aiming at lower startup power consumption, stronger thermal load adaptability, easier parameters adjustment, and higher parameter tuning efficiency for the temperature control system of a distributed Bragg reflector (DBR) semiconductor laser, this paper employs the double-loop control and intelligent parameter tuning methods. First, the thermal equivalent circuit model is established for the laser temperature control system, which has stronger thermal load adaptability than the traditional transfer function model. In order to improve the modeling speed and accuracy, a mean impact value (MIV) quantum particle swarm optimization (QPSO) intelligent algorithm is proposed to tune the model parameters. A double-loop temperature control system is set up on this basis. Then, the MIV-QPSO intelligent algorithm is used to tune the control parameters, which shortens the settling time, increases the tuning efficiency, and improves the temperature control effect. The feasibility and effectiveness of the proposed methods are verified through the MATLAB/Simulink simulation of the laser temperature control process.

This paper investigates the laser polarization error in the optical rotation detection system (ORDS) of an atomic comagnetometer (ACM), which will seriously degrade the long-term performance of the ORDS. We first establish an optical transmission model of the ORDS by using Jones matrix concerning the optical imperfection of polarizers. Then, we analyze the polarization error based on this model and propose a novel error suppression method. Finally, we experimentally test the long-term performance of the ORDS and the ACM before and after the polarization error suppression to verify the effectiveness of the proposed method. The experimental results show that the long-term performance of the ORDS and the ACM can be improved by approximately 3.4 times with the proposed polarization error suppression method.

The elimination of relaxation resulting from spin-exchange (SE) interaction is crucial for ultrasensitive atomic comagnetometers. In this study, we demonstrate the SE relaxation is only partially suppressed and significantly broadens the magnetic linewidth in the K-Rb- 21 Ne comagnetometer. The SE relaxation arises from the compensation magnetic field when operating in the self-compensation regime. We propose a new method to measure the SE relaxation in the self-compensation regime where the alkali-metal and noble-gas spin ensembles are coupled. In the presence of SE relaxation, we find the optimal alkali-metal polarization for maximizing the sensitivity is shifted from the typical value. Under various conditions, we present a detailed study of the SE relaxation and the scale factor as a function of alkali-metal polarization, which are further verified by the theoretical models. The reduction of SE relaxation and improvement of scale factor by using 87 Rb atoms is also studied.

We demonstrate a new method to determine the nuclear magnetic field of the spin-exchange optically pumped noble gas in a self-compensated atomic comagnetometer based on the steady-state AC response. The result shows that it has higher resolution and precision than a previous method based on the transient process. Furthermore, a convergence frequency is observed in the low-frequency region and its parameter dependence is studied simulatively, which may inspire further research into its relationship with the strong suppression mechanism of the self-compensation ability for the low-frequency magnetic field. We also prove that this method can be developed for suppression of residual main magnetic field to improve the systematic stability of the comagnetometer.

A novel method to control the light intensity stability and modulate the probe light polarization using a liquid crystal variable retarder (LCVR) to detect atomic spin precession simultaneously in a K-Rb- 21 Ne gyroscope is reported. A sinusoidal driving voltage is applied to drive the LCVR and is skillfully used to produce a high-frequency modulation for the probe light. The modulation helps to avoid electronic detection noise appearing at low frequencies and allows for phase-sensitive detection. The coefficient of rate ramp can be reduced from 1.31 (deg/h)/h to 0.05 (deg/h)/h (Allan deviation), and the bias instability of about 0.08 deg/h at the averaging time of 200 s is achieved. Therefore, the long-term stability of the angular velocity measurement can be improved and other optical modulators can be replaced to facilitate the miniaturization of the gyroscope by using this intensity modulation detection method. This optical rotation detection method also can be applied to other miniaturized atomic sensors, such as atomic magnetometers.

We investigate the effects of pump laser power density on the hybrid optically pumped comagnetometer operated in the spin-exchange relaxation-free (SERF) regime. The analytic steady-state output model for the comagnetometer considering two alkali metal species and one nuclear species is presented for the first time. And the effects of pump laser power density on the rotation sensitivity, suppression of low-frequency magnetic noise and long-term stability of the comagnetometer are studied experimentally. The results indicate that when the product of pumping rate and density ratio of pumped atom to probed atom is equal to the spin relaxation rate of the probed atom, the maximum response and highest sensitivity of the comagnetometer are achieved. However, the suppression of low-frequency magnetic noise and long-term stability improve with the increasing of pump laser power density due to the increasing of nuclear spin polarization. Our focus is to optimize the performance of the comagnetometer for rotation sensing, but the theory and method presented here are relevant to all applications of the hybrid optical pumping technique.

We investigate a new method that enables the direct measurement of the density ratio of a K-Rb hybrid vapor cell, using the spin-exchange collision mixing of the K and Rb light shifts. The densities for each alkali metals can be further determined using Raoult's law. The mixture of the light shifts in both magnetometers and comagnetometers is formulated using Bloch equations and explained by considering the fast spin-exchange interaction. The relationship between the density ratio and the mixed light shifts is both formulated and simulated. The method was performed on several K-Rb magnetometer- and K-Rb- 21 Ne comagnetometer-cells at different temperatures, pump light powers, and mole fractions of K. The method was further verified by the conventional laser-absorption-spectroscopy method. The new approach has the advantage to measure the density ratio of the optically-thick hybrid alkali atoms, while requiring no additional magnetic field necessary for conventional magnetic-field induced Faraday-rotation techniques. It also has the advantage of in-situ measuring the density ratio under exactly the normal operation of the devices, which means that the errors caused by the heating-effect of the strong pump light and the temperature drift during long-term operation can be real-time monitored.

The number density of alkali metal vapors and their ratio within hybrid cells is of great significance for the optimal rotation sensitivity of alkali metal-noble gas comagnetometers. To measure the number density of optically thick Rb vapor accurately within a hybrid cell containing optically thin K vapor and optically thick Rb vapor, a novel method combining alkali metal absorption spectroscopy and Raoult's law is proposed in this paper. The relative error between experimental results and results calculated by empirical formula is within ±5% from 365 to 450 K, and the measurement accuracy is improved more than 10 times compared to previous study. This novel method could be applied to check the number density ratio of alkali metal within hybrid cells more precisely.

A dual-axis atomic comagnetometer can sense the angular rotation of two measurement axes simultaneously and independently. However, there is a cross-talk coupling effect between the two axes because of the residual magnetic field and the light shift arising from the pumping laser. Here, we propose a scheme to eliminate the rotation coupling of dual-axis K-Rb-N21e atomic comagnetometers. The residual magnetic field can be effectively removed by controlling the comagnetometer at the magnetic compensation point and the magnetic shielding layer. The light shift could be eliminated by using the K atom light shift to counteract the Rb atom light shift, in which the light shift of K atoms was optimized to the decoupling point by finely adjusting the pumping laser wavelength of the K D1 line. The feasibility and efficiency of this decoupling scheme have been experimentally verified. The output response of the coupling axis is reduced by two orders of magnitude compared to the sensitive axis. This scheme can also be applied to any atomic comagnetometer with hybrid optical pumping that experiences cross-talk coupling.

Optical rotation of linearly polarized light is used to measure atom spin precession in an atomic spin gyroscope (ASG). However, the common-mode noise in the polarization measurement seriously affects the performance of the sensitive ASG. Here we propose an optical differential detection method based on the photoelastic polarization modulation, which could effectively eliminate the light power fluctuation of the laser source and optical elements, while removing the polarization noise and the residual birefringence. The feasibility and efficiency of this method have been verified experimentally. The rotation sensitivity of the ASG is an order of magnitude better, and the long-time stability is significantly improved. In addition, this method is easier to implement because noise sources do not need to be strictly distinguished.

A method for simultaneously calibrating the peak retardation and static retardation of a photoelastic modulator (PEM) is proposed. By optimizing the polarization modulation system, the normalized fundamental frequency components of the modulation signals are obtained to calculate the peak retardation and static retardation of the PEM. The calibration result is immune to fluctuations of the incident light intensity and can be used to correct the deviation of the photoelastic modulation detection results. In our experiments, the average deviation between measured peak retardations and corresponding set values is 0.0339 rad. The standard deviation between the measured static retardations and the average measured value is 0.0003 rad. The calibration method has a high sensitivity, since the large gradient of the first-order Bessel function when the peak retardation is less than 1 rad. The experimental results are consistent with the theoretical analysis.

We demonstrate a novel method of measuring magnetic field based on the transient signal of the K-Rb- 21 Ne co-magnetometer operating in nuclear spin magnetization self-compensation magnetic field regime. The operation condition for self-compensation magnetic field by nuclear spin magnetization of 21 Ne in steady state is presented. We characterize the dynamics of the coupled spin ensembles by a set of Bloch equations, and formulate the expression of transient output signal. After verifying the stability of this method, the measurement range and error are studied. This method is also verified to be valid in various temperature and pumping light power density.

We conceive an improved procedure to determine the laser intensity with the momentum distributions from nonadiabatic tunneling ionization of atoms in the close-to-circularly polarized laser fields. The measurements for several noble gas atoms are in accordance with the semiclassical calculations, where the nonadiabatic effect and the influence of Coulomb potential are included. Furthermore, the high-order above-threshold ionization spectrum in linearly polarized laser fields for Ar is measured and compared with the numerical calculation of the time-dependent Schrödinger equation in the single-active-electron approximation to test the accuracy of the calibrated laser intensity.

Filamentation dynamics in fused silica are investigated using an Airy pattern and a Gaussian laser beam. The angle-resolved conical emission spectra are measured and compared with the predictions of several models. Our experimental observations are consistent with the X-waves model in both cases. This indicates that both laser beams spontaneously evolve into nonlinear X-waves and suggests a universal evolution of filaments in fused silica, regardless of the initial laser beam profile.

We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

We demonstrate a method for self-compensation of scale factor changes of an interferometric fiber-optic current sensor caused by source wavelength shifts, e.g., due to changes in source temperature or drive current. An adequately tailored fiber-optic retarder in the optical circuit introduces wavelength-dependent mixing of the orthogonal polarization modes of the sensor. The resulting change in scale factor balances the variation of the Faraday effect with wavelength. The wavelength dependence of the sensor is suppressed by more than an order of magnitude to <0.2% over wavelength spans of at least 10 nm around 1305 nm. The retarder is designed as an athermal device for operation between -40°C and 80°C.

A BOTDA sensing scheme combined frequency sweeping and slope-assisted techniques is proposed and experimentally demonstrated for simultaneously temperature and strain-induced vibration sensing. In this scheme, during sweeping Brillouin gain spectrum (BGS) for temperature measurement, we simultaneously perform FFT to the time-domain traces whose probe-pump frequency difference (PPFD) is within the FWHM of the BGS at each position of fiber, and the location and the frequency of the strain-induced vibration event can be acquired based on SA-BOTDA technique. In this way, the vibration can be continuously measured at each selected working frequency point during the BGS scanning process and multiple measurements of vibration event can be completed in one whole BGS scanning process. Meanwhile, double sidebands probe method is employed to reduce the nonlocal effects. In our experiment, a temperature event and two vibration events with the frequency of 7.00Hz or 10.00Hz are simultaneously measured near the end of 10.6km long sensing fiber in a traditional BOTDA system. The system shows 1.2°C temperature accuracy and 0.67Hz frequency resolution, as well as a 3m spatial resolution. The proposed method may find some potential applications where both the strain-induced vibration frequency and temperature are the diagnostic objects.

We propose a far off-resonance laser frequency stabilization method by using multipass cells in Rb Faraday rotation spectroscopy. Based on the detuning equation, if multipass cells with several meters optical path length are used in the conventional Faraday spectroscopy, the detuning of the lock point can be extended much further from the alkali metal resonance. A plate beam splitter was used to generate two different Faraday signals at the same time. The transmitted optical path length was L=50  mm and the reflected optical path length was 2L=100  mm. When the optical path length doubled, the detuning of the lock points moved further away from the atomic resonance. The temperature dependence of the detuning of the lock point was also analyzed. A temperature-insensitive lock point was found near resonance when the cell temperature was between 110°C and 130°C. We achieved an rms fluctuation of 0.9 MHz/23 h at a detuning of 0.5 GHz. A frequency drift of 16 MHz/h at a detuning of -5.6  GHz and 4 MHz/h at a detuning of -5.2  GHz were also obtained for the transmitted and reflected light Faraday signal.

The objectives of this study are to validate the applicability of a three-band algorithm in determining chlorophyll-a in eutrophic coastal waters, and to improve the model using improved three-band algorithm. Evaluated using two independent data sets collected from the West Florida Shelf, the variation three-band model was found to have a superior performance to both the three-band and modified three-band model. Using the variation three-band algorithm decreased 18% and 56% uncertainty, respectively, from the three-band and modified three-band algorithms. The significantly reduced uncertainty in chlorophyll-a estimations is attributed to effective removal of absorption of gelbstoff and suspended solids and backscattering of water molecules.

A simple semi-analytical model (SAB) was developed for computing a(560) and b(b)(550) from HJ-1A/CCD images. By comparison with field measurements, the SAB model produces 5.3-23.5% uncertainty for a(560) and b(b)(550) retrievals. The a(560) and b(b)(550) are also retrieved from satellite images. The match-up analysis results indicate that a(560) and b(b)(550) may be derived from the HJ-1A/CCD images with respective uncertainties of 29.84 and 21.35%. These findings imply that, provided that an atmospheric correction scheme for the green bands is available, the extensive database of HJ-1A/CCD imagery may be used for the quantitative monitoring of optical properties in coastal waters.