With the help of Stokes operator Ŝ2 squeezed state (also called polarization squeezed state (PSS)) of 795 nm light, rubidium-87 (87Rb) atomic magnetometer based on Faraday rotation (FR) has been implemented and characterized. The PSS of Stokes operator Ŝ2 of 795 nm light has been prepared by means of coherently combining the polarization coherent state (PCS) of a linearly p-polarized bright 795 nm light beam and a linearly s-polarized squeezed vacuum state (SVS) generated by a 397.5 nm ultraviolet laser pumped sub-threshold optical parametric oscillator (OPO) with a PPKTP bulk crystal inside the OPO cavity. PSS with a squeezing level of −3.7 ± 0.3 dB has been achieved around the analysis frequency of 10 kHz. At different transitions of D1 line, various frequency detuning, and reasonable atomic vapor cell’s temperature, FR has been measured and compared. To decrease absorption (scattering) losses and the back-action from atomic spin noise to the probe beam’s polarization noise for maintaining the quantum properties of PSS of Stokes operator Ŝ2 of 795 nm light, we had to run our magnetometer with 87Rb vapor cell’s temperature below 60 °C, at which the PSS was almost destroyed. The sensitivities of magnetic field measurement were characterized via measuring signal-to-noise ratio of the alternating current calibrated magnetic field signal with a balanced polarimeter. Under the conditions of the atomic number density of ∼5.8 × 1010 cm−3 (T ∼ 40 °C) and the probe beam with a detuning of ∼−400 MHz relative to the 5S1/2 (F g = 2) − 5P1/2 (F e = 1) transition of 87Rb D1 line, a typical sensitivity of ∼19.5 pT (Hz1/2)−1 has been achieved employing PSS of Stokes operator Ŝ2 as the probe, compared with a sensitivity of ∼28.3pT (Hz1/2)−1 using PCS as the probe. We preliminarily demonstrated that the quantum-enhanced sensitivity in a Faraday-rotation-based 87Rb atomic magnetometer with the help of PSS of 795 nm light.

Laser intensity noise suppression has essential effects on preparation and characterization of the audio-frequency squeezed vacuum state of light based on a sub-threshold optical parametric oscillator (OPO).We have implemented two feedback loops by using relevant acousto-optical modulators (AOM) to stabilize the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm ultraviolet (UV) laser generated by cavity-enhanced frequency doubling.Typical peak-to-peak laser intensity fluctuation with a bandwidth of ∼ 10 kHz in a half hour has been improved from ±7.45% to ±0.06% for 795-nm NIR laser beam, and from ±9.04% to ±0.05% for 397.5-nm UV laser beam, respectively. The squeezing level of the squeezed vacuum state at 795 nm prepared by the sub-threshold OPO with a PPKTP crystal has been improved from -3.3 to -4.0 dB around 3∼9 kHz of audio analysis frequency range.

For the experimental implementation of an optically pumped atomic magnetometer, the magnetic resonance signal with a narrow linewidth and a high signal-to-noise ratio (SNR) is required for achieving a high sensitivity. Using 795-nm laser as both the pumping and the probe laser, we compare the magnetic resonance signals from different rubidium atomic vapor cells and investigate the variations of magnetic resonance signals with temperature. Optimized magnetic resonance signal is achieved with a paraffin-coated rubidium atomic vapor cell. Then the 780-nm laser at rubidium D2 line is introduced as a repumping laser, and we explore the changes of linewidth and SNR of the magnetic resonance signal under different power of the pumping laser and the repumping laser. Owing to the 780-nm repumping laser beam, the signal amplitude of rubidium-85 magnetic resonance signal is improved remarkably because more rubidium-85 atoms are spin- polarized by the 795-nm pumping laser beam. At the same time, the linewidth of rubidium-85 magnetic resonance signal is roughly not broadened anymore. We realize a closed-loop optically pumped rubidium-85 atomic magnetometer with a bandwidth of ~1.2 kHz, and the sensitivity is calibrated to be ~245.5 pT/Hz^1/2 only with the 795-nm pumping laser beam. Owing to the employment of the 780-nm repumping laser beam, the sensitivity is improved to be ~26.4 pT/Hz^1/2 which is improved roughly by one order of magnitude. We also calibrate the measurement accuracy and deviation of a commercial fluxgate magnetometer by using the enhanced rubidium magnetic resonance signal.

Thin-walled parts are typically difficult-to-cut components due to the complex dynamics in cutting process. The dynamics is variant for part during machining, but invariant for machine tool. The variation of the relative dynamics results in the difference of cutting stage division and cutting parameter selection. This paper develops a novel method for whole cutting process optimization based on the relative varying dynamic characteristic of machining system. A new strategy to distinguish cutting stages depending on the dominated dynamics during machining process is proposed, and a thickness-dependent model to predict the dynamics of part is developed. Optimal cutting parameters change with stages, which can be divided by the critical thickness of part. Based on the dynamics comparison between machine tool and thickness-varying part, the critical thicknesses are predicted by an iterative algorithm. The proposed method is validated by the machining of three benchmarks. Good agreements have been obtained between prediction and experimental results in terms of stages identification, meanwhile, the optimized parameters perform well during the whole cutting process.

We measured the spin noise spectroscopy (SNS) of rubidium atomic ensemble with two different kinds of atomic vapor cells (filled with buffer gas or coated with paraffin film on the inner wall) and demonstrated the enhancement of the signal-to-noise ratio (SNR) by using polarization squeezed state (PSS) of 795-nm light field with Stokes operator S Λ 2 squeezed. The PSS is prepared by locking the relative phase between the squeezed vacuum state of light obtained with a sub-threshold optical parametric oscillator and the orthogonally polarized local oscillator beam by means of the quantum noise lock. Under the same conditions, the PSS can be employed not only to improve the SNR, but also to keep the full width at half maximum (FWHM) of SNS, compared with the case of using the polarization coherent state (PCS), enhancement of SNR is positively correlated with the squeezing level of the PSS. With increasing probe laser power and atomic number density, the SNR and FWHM of SNS will increase correspondingly. With the help of the PSS of the Stokes operator S Λ 2 , quantum improvements of both the SNR and FWHM of SNS signal has been demonstrated by controlling optical power of polarization squeezed light beam or atomic number density in our experiments.