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Based on a low-noise cesium spectral lamp, a high-sensitivity self-oscillating cesium atomic magnetometer with a wide operating temperature range has been developed, solving problems with existing sensors such as a limited operating temperature range and difficult startup at low temperatures. The temperature feedback mechanism is used to make adjustments to any fluctuations in the cesium lamp's excitation source in real time, improving the magnetometer's stability and operating temperature range. Herein, the design and optimization of the cesium atomic magnetometer are presented, and a prototype of the magnetometer is described. The quantum limit sensitivity of the cesium atomic magnetometer is estimated by evaluating the intrinsic relaxation rate in the geomagnetic field. A test demonstrates that the cesium atomic magnetometer's sensitivity in the geomagnetic background is around 140   f T / H z at 1 Hz at room temperature, and the operating temperature range is from −50 °C to 70 °C, surpassing most of the commercial products of its kind in terms of sensitivity and operating temperature range. [ABSTRACT FROM AUTHOR]

Herein, we report the scheme of an optically pumped atomic clock based on a cold cesium atomic beam source. We propose the laser system and physical mechanism of this atomic clock, wherein the atomic beam travels in an upper parabolic trajectory, thereby eliminating the light shift effect. In the experiments, when the length of the free evolution region was 167 mm, the line width of the Ramsey fringe was 37 Hz. When the expected signal-to-noise ratio of the Ramsey fringe that can be achieved is 36,000, the expected short-term frequency stability is about 3.6 × 10–14/√τ, which is significantly higher than that of a conventional optically pumped cesium clock of similar volume.

The research of optically pumped cesium beam atomic clock (OPCB) at Peking University has lasted for decades. At present, the short-term frequency stability is 3×10−12/τ and the long-term (5-day) frequency stability can reach 7 × 10−15. The optimization methods of the short-term frequency stability are using laser induced beam spectrum to stabilize the laser frequency, using cyclic transition to detect the atomic state and using a cesium oven with a collimator to generate the cesium atomic beam. The methods of obtaining the good long-term frequency stability are controlling the microwave power based on the atomic transition probability, controlling the C-field intensity based on Zeeman frequency and controlling the laser power using fluorescence. The compact optically pumped cesium beam atomic clock of Peking University is expected to contribute to the field of timing, positioning, navigation and high speed digital communication.

Based on a low-noise cesium spectral lamp, a high-sensitivity self-oscillating cesium atomic magnetometer with a wide operating temperature range has been developed, solving problems with existing sensors such as a limited operating temperature range and difficult startup at low temperatures. The temperature feedback mechanism is used to make adjustments to any fluctuations in the cesium lamp’s excitation source in real time, improving the magnetometer’s stability and operating temperature range. Herein, the design and optimization of the cesium atomic magnetometer are presented, and a prototype of the magnetometer is described. The quantum limit sensitivity of the cesium atomic magnetometer is estimated by evaluating the intrinsic relaxation rate in the geomagnetic field. A test demonstrates that the cesium atomic magnetometer’s sensitivity in the geomagnetic background is around 140 fT/Hz at 1 Hz at room temperature, and the operating temperature range is from −50 °C to 70 °C, surpassing most of the commercial products of its kind in terms of sensitivity and operating temperature range.

In order to get a better tradeoff between the long lifetime and high performances of cesium beam atomic clocks, we proposed a design scheme of compact optically pumped cesium beam tube (OPCBT) based on hexapole magnetic focusing (HMF) system for the confinement of cesium. A practical optically pumped cesium beam tube without HMF system has been implemented and tested with high-stability laser by modulation transfer spectroscopy (MTS), and a signal-to-noise ratio (SNR) of 18,000 in 1 Hz bandwidth and Allan deviation of 2×10−12/τ were obtained. Based on this test, the simulation analysis results of the newly designed tube with HMF show that the predicted lifetime can reach over 20 years without degradation of the performances, and the expected frequency stability of the clock can be 6.5×10−13/τ with a lifetime of 10 years.

We report here an optically pumped deep UV edge emitting laser with AlGaN multiple quantum wells (MQWs) active region grown on AlN substrate by low pressure organometallic vapor phase epitaxy (LP-OMVPE) in a high-temperature reactor. The 21 period Al0.53Ga0.47N/Al0.7Ga0.3N MQWs laser structure was optically pumped using 193 nm deep UV excimer laser source. A laser peak was achieved from the cleaved facets at 280.3 nm with linewidth of 0.08 nm at room temperature with threshold power density of 320 kW/cm2. The emission is completely TE polarized and the side mode suppression ratio (SMSR) is measured to be around 14 dB at 450 kW/cm2.

Abstract We reported the selective area growth (SAG) of semipolar { 11 2 ̅ 2 } InGaN/GaN multiple quantum wells (MQWs) laser diodes (LDs) on the patterned GaN/AlN/Si (111) templates. For GaN (0001) on Si (111), the natural cleavage planes of GaN { 1 1 ̅ 00 } and Si { 11 2 ̅ } are aligned. In this work, the templates were patterned with stripe windows oriented along GaN [ 1 1 ̅ 00 ] direction. Utilizing a two-step SAG method, the semipolar GaN-based laser structures were successfully deposited on the inclined { 11 2 ̅ 2 } facets of the laser stripes. STEM measurements indicated the upper areas of inclined { 11 2 ̅ 2 } facets are nearly defect free due to the bending effect of TDs. The cavity facets were produced by cleaving method. Stimulated emission was achieved under optical pumping at room temperature, showing a threshold pump power density of 1.85 MW/cm2, which was attributed to the low defect and small internal field on the upper areas of semipolar { 11 2 ̅ 2 } facets selectively grown on the Si (111) substrates. [ABSTRACT FROM AUTHOR]

Based on our four-level rate equations model, we analyze through numerical simulations the dynamics of the electron density, population inversion and terahertz intensity present within the cavity of a mid-infrared optically pumped electrically driven THz quantum cascade laser. We find in particular that the mid-infrared pump intensity influences significantly the dynamical behavior of the present device. Moreover, compared to its homologue, the conventional electrically injected THz quantum cascade laser, this system presents much faster dynamics. In addition, within the premises of our model, we derive in the most general case the equation that allows for the determination of the turn-on delay time t th . [ABSTRACT FROM AUTHOR]

A four level rate equations model for a terahertz optically pumped electrically driven quantum cascade laser is here introduced and used to model the system both analytically and numerically. In the steady state, both in the presence and absence of the terahertz optical field, we solve the resulting nonlinear system of equations and obtain closed form expressions for the levels occupation, population inversion as well as the mid-infrared pump threshold intensity in terms of the device parameters. We also derive, for the first time for this system, an analytical formula for the optical external efficiency and analyze the simultaneous effects of the cavity length and pump intensity on it. At moderate to high pump intensities, we find that the optical external efficiency scales roughly as the reciprocal of the cavity length. [ABSTRACT FROM AUTHOR]

An improved one-step leapfrog alternating-direction-implicit finite-difference time-domain (ADI-FDTD) method is proposed to study surface plasmon polaritons (SPPs) in optically pumped and electrostatic applied curved graphene structures, with their intraband and interband surface conductivities modeled with the vector fitting technique. Such a method can quickly capture the broadband characteristics of SPPs propagating along monolayer, bilayer and trilayer graphene sheets of arbitrary shapes. Numerical stability and accuracy are validated through characterizing field distributions of the SPPs supported in the 180°-curved and spiral graphene sheet waveguides and higher computational efficiency are achieved in comparison with the conventional FDTD method. [ABSTRACT FROM AUTHOR]

Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented [ABSTRACT FROM PUBLISHER]

Thermal index changes due to nonradiative relaxation in optically pumped Co2+-doped and Vn+ doped fibers are studied experimentally by an interferometric method. In both dopants these effects are shown to be very strong and to mask any residual resonantly enhanced nonlinearity. The measured magnitude and time constants of thermal effects are well explained by a new theoretical model, which confirms its validity and usefulness. These measurements also demonstrate a new and simple method to differentiate between nonlinear and thermal phase shifts in doped fibers based on the dependence of the phase change on the pump pulsewidth. This study provides new information on the spectroscopy of these two dopants, including the percentage of absorbed power they transform into heat (~38% for Co2+ and 56% for Vn+), and the likely presence of clusters in Co2+-doped silica even at very low concentrations (8 wt ppm CoO) [ABSTRACT FROM PUBLISHER]

Abstract: A high beam quality 978nm vertical external cavity surface emitting lasers pumped by circular beam spot is presented. The VECSEL wafer contains 13 resonant periodic gains, which consisted of strain quantum-wells compensated symmetrically, and double-band mirror. 740mW 978nm and near-diffraction limit (M 2 =1.05) circular symmetry laser beam is obtained when pumped power is 3.9W, optical conversion efficiency is 18.97% and slope efficiency is 35.2%. [Copyright &y& Elsevier]

Quantum-dot vertical-external-cavity surface-emitting lasers (QD VECSELs) are of interest due to their large inhomogeneous gain spectrum and the potential for temperature insensitivity and low threshold. We report a QD VECSEL which is wetting-layer-pumped using a 915-nm diode laser, reducing the quantum defect compared to barrier pumping. A slope efficiency of 56% relative to absorbed pump power was measured from an unprocessed sample with a heat-sink temperature of -30 °C, 1.75 × higher than when barrier pumped using an 830-nm pump diode. [ABSTRACT FROM PUBLISHER]

An optically pumped long-wavelength vertical-cavity surface-emitting laser (VCSEL) with resonant optical pumping has been proposed. The proposed structure enables the dual-resonance of pump light (1300 nm band) and output light (1550 nm band) at the same time. It is shown that high pumping efficiency of ∼90% can be obtained by adjusting the top mirror reflectivity and the cavity length. This dual-resonance VCSEL (DR-VCSEL) may have great advantages of high efficiency pumping, low power consumption and can be fabricated by using conventional VCSEL fabrication techniques with reasonable fabrication tolerances. [ABSTRACT FROM AUTHOR]

We demonstrate all-optical switching in a laterally coupled GaAs-AlGaAs microring resonator by carriers injections. The ring waveguide is optically pumped just above its bandgap energy, which results in a temporal tuning of the microring resonant wavelengths by the refractive index change due to the induced carriers. A switching window of 20 ps could be obtained and is only limited by the carrier recombination time. A switching energy of a few tens of picojoules per pulse is used and has resulted in a 1.2-nm wavelength shift of the microring resonance. [ABSTRACT FROM PUBLISHER]

Room-temperature operation of two-dimensional photonic crystal lasers optically pumped by a vertical-cavity surface-emitting laser emitting at 860 nm is reported. The photonic crystal membrane is surrounded by air on both sides and consists of four compressively strained quantum wells as the active region. The incident threshold pump power of an approximately 2.6-μm-diameter hexagonal defect cavity laser operating at 1.6 μm is 2.4 mW [ABSTRACT FROM PUBLISHER]

The modulation/switching properties of a vertical-cavity semiconductor optical amplifier operating at 1.3 μm wavelength are investigated. The device was optically pumped and operated in reflection mode. A 150-mV (100 mA) modulation of the drive to the pump source produced a 7-dB modulation of the pump power, which produced a 35-dB modulation in the output signal. The maximum extinction ratio was 35 dB, and limited by device heating. Frequency response measurements revealed a modulation bandwidth of 1.8 GHz when the amplifier was saturated. This enabled 2.5-Gb/s modulation of a -10 dBm input signal with 5.5-dB fiber-to-fiber gain [ABSTRACT FROM PUBLISHER]

Vertical cavity lasers operating at a wavelength of 1547 nm were optically pumped by a 980-nm diode laser. Continuous-wave fiber-coupled output powers of 2 mW at room temperature and 140 nW at 105°C were observed. Fiber optic transmission over 25 km at 6 Gbit/s with a power penalty of 0.3 dB was demonstrated [ABSTRACT FROM PUBLISHER]