Stable CW laser based on low thermal expansion ceramic cavity with 4.9 mHz/s frequency drift

Low phase noise cavity transmission self-injection locked diode laser system for atomic physics experiments

Lasers with high spectral purity are indispensable for optical clocks and for the coherent manipulation of atomic and molecular qubits in applications such as quantum computing and quantum simulation. While the stabilization of such lasers to a reference can provide a narrow linewidth, the widely used diode lasers exhibit fast phase noise that prevents high-fidelity qubit manipulation. In this paper, we demonstrate a self-injection locked diode laser system that utilizes a high-finesse cavity. This cavity not only provides a stable resonance frequency, it also acts as a low-pass filter for phase noise beyond the cavity linewidth of around 100 kHz, resulting in low phase noise from dc to the injection lock limit. We model the expected laser performance and benchmark it using a single trapped 40Ca+-ion as a spectrum analyzer. We show that the fast phase noise of the laser at relevant Fourier frequencies of 100 kHz to >2 MHz is suppressed to a noise floor of between -110 dBc/Hz and -120 dBc/Hz, an improvement of 20 to 30 dB over state-of-the-art Pound-Drever-Hall-stabilized extended-cavity diode lasers. This strong suppression avoids incoherent (spurious) spin flips during manipulation of optical qubits and improves laser-driven gates when using diode lasers in applications involving quantum logic spectroscopy, quantum simulation, and quantum computation.

200-Hz longitudinal-mode linewidth found in a free-running mode-locked Yb:fiber laser

We surveyed the longitudinal-mode linewidth of five homemade mode-locked Yb:fiber lasers by taking the beat note with a Hz-level narrow-linewidth CW laser. We systematically varied the resolution bandwidth of the spectrum analyzer and found that the linewidth can be as narrow as 200 Hz, which surpassed the records for free-running mode-locked lasers in the literature to our best knowledge. Based on the survey, we propose that making the cavity long and simple is a good working hypothesis for narrowing the linewidth and provide practical techniques to reduce the environmental fluctuations.

Piezo-electric transducer actuated mirror with a servo bandwidth beyond 500 kHz

We demonstrate a novel system that uses a piezoelectric transducer (PZT)-actuated mirror for laser stabilization. A combination of a simple mechanical design and electronic circuits is used to realize an ultra-flat frequency response, which enables an effective feedback bandwidth of 500 kHz. The PZT also performed well when used in a mode-locked laser with a GHz repetition rate, to which it is difficult to apply an electro-optic modulator (EOM).

A simplified cryogenic optical resonator apparatus providing ultra-low frequency drift

A system providing an optical frequency with instability comparable to that of a hydrogen maser is presented. It consists of a 5 cm long, vertically oriented silicon optical resonator operated at temperatures between 1.5 K and 3.6 K in a closed-cycle cryostat with a low-temperature Joule-Thomson stage. We show that with a standard cryostat, a simple cryogenic optomechanical setup, and no active or passive vibration isolation, a minimum frequency instability of 2.5 × 10^-15 at τ = 1500 s integration time can be reached. The influence of pulse-tube vibrations was minimized by using a resonator designed for low acceleration sensitivity. With reduced optical laser power and interrogation duty cycle, an ultra-low fractional frequency drift of -2.6 × 10^-19/s is reached. At 3.5 K, the resonator frequency exhibits a vanishing thermal sensitivity and an ultra-small temperature derivative 8.5 × 10^-12/K². These are favorable properties that should lead to high performance also in simpler cryostats not equipped with a Joule-Thomson stage.

The Anisotropic Thermal Expansion of Non-linear Optical Crystal BaAlBO3F2 Below Room Temperature

Thermal expansion is a crucial factor for the performance of laser devices, since the induced thermal stress by laser irradiation would strongly affect the optical beam quality. For BaAlBO₃F₂ (BABF), a good non-linear optical (NLO) crystal, due to the highly anisotropic thermal expansion its practical applications are strongly affected by the “tearing” stress with the presence of local overheating area around the laser spot. Recently, the strategy to place the optical crystals in low-temperature environment to alleviate the influence of the thermal effect has been proposed. In order to understand the prospect of BABF for this application, in this work, we investigated its thermal expansion behavior below room temperature. The variable-temperature XRD showed that the ratio of thermal expansion coefficient between along c- and along a(b)- axis is high as 4.5:1 in BABF. The Raman spectrum combined with first-principles phonon analysis revealed that this high thermal expansion anisotropy mainly ascribe to progressive stimulation of the respective vibration phonon modes related with the thermal expansion along a(b)- and c-axis. The good NLO performance in BABF can be kept below room temperature. The work presented in this paper provides an in-depth sight into the thermal expansion behavior in BABF, which, we believe, would has significant implication to the manipulation in atomic scale on the thermal expansion of the materials adopted in strong-field optical facility.