A Cold-Atom Interferometer with Microfabricated Gratings and a Single Seed Laser

The extreme miniaturization of a cold-atom interferometer accelerometer requires the development of novel technologies and architectures for the interferometer subsystems. We describe several component technologies and a laser system architecture to enable a path to such miniaturization. We developed a custom, compact titanium vacuum package containing a microfabricated grating chip for a tetrahedral grating magneto-optical trap (GMOT) using a single cooling beam. The vacuum package is integrated into the optomechanical design of a compact cold-atom sensor head with fixed optical components. In addition, a multichannel laser system driven by a single seed laser has been implemented with time-multiplexed frequency shifting using single sideband modulators, reducing the number of optical channels connected to the sensor head. This laser system architecture is compatible with a highly miniaturized photonic integrated circuit approach, and by demonstrating atom-interferometer operation with this laser system, we show feasibility for the integrated photonic approach. In the compact sensor head, sub-Doppler cooling in the GMOT produces 15 μK temperatures, which can operate at a 20 Hz data rate for the atom interferometer sequence. After validating atomic coherence with Ramsey interferometry, we demonstrate a light-pulse atom interferometer in a gravimeter configuration without vibration isolation for 10 Hz measurement cycle rate and T = 0 - 4.5 ms interrogation time, resulting in Δg/g = 2.0e-6. All these efforts demonstrate progress towards deployable cold-atom inertial sensors under large amplitude motional dynamics.

A coherent harmonic generation method for producing femtosecond coherent radiation in a laser plasma accelerator based light source

The electron beam generated in laser plasma accelerators (LPAs) has two main initial weaknesses – a large beam divergence (up to a few milliradians) and a few percent level energy spread. They reduce the beam brightness and worsen the coherence of the LPA-based light source. To achieve fully coherent radiation, several methods have been proposed for generating strong microbunching on LPA beams. In these methods, a seed laser is used to induce an angular modulation into the electron beam, and the angular modulation is converted into a strong density modulation through a beamline with nonzero longitudinal position and transverse angle coupling. In this paper, an alternative method to generate microbunching into the LPA beam by using a seed laser that induces an energy modulation and transverse–longitudinal coupling beamlines that convert the energy modulation into strong density modulation is proposed. Compared with the angular modulation methods, the proposed method can use more than one order of magnitude lower seed laser power to achieve similar radiation performance. Simulations show that with the proposed method a coherent pulse of a few microjoules pulse energy and femtosecond duration can be generated with a typical LPA beam.

Amplification by stimulated emission of nitrogen-vacancy centres in a diamond-loaded fibre cavity

Laser threshold magnetometry using the negatively charged nitrogen-vacancy (NV−) centre in diamond as a gain medium has been proposed as a technique to dramatically enhance the sensitivity of room-temperature magnetometry. We experimentally explore a diamond-loaded open tunable fibre-cavity system as a potential contender for the realisation of lasing with NV− centres. We observe amplification of the transmission of a cavity-resonant seed laser at 721 nm when the cavity is pumped at 532 nm and attribute this to stimulated emission. Changes in the intensity of spontaneously emitted photons accompany the amplification, and a qualitative model including stimulated emission and ionisation dynamics of the NV− centre captures the dynamics in the experiment very well. These results highlight important considerations in the realisation of an NV− laser in diamond.

Basic Reinforcement Learning Techniques to Control the Intensity of a Seeded Free-Electron Laser

Optimal tuning of particle accelerators is a challenging task. Many different approaches have been proposed in the past to solve two main problems—attainment of an optimal working point and performance recovery after machine drifts. The most classical model-free techniques (e.g., Gradient Ascent or Extremum Seeking algorithms) have some intrinsic limitations. To overcome those limitations, Machine Learning tools, in particular Reinforcement Learning (RL), are attracting more and more attention in the particle accelerator community. We investigate the feasibility of RL model-free approaches to align the seed laser, as well as other service lasers, at FERMI, the free-electron laser facility at Elettra Sincrotrone Trieste. We apply two different techniques—the first, based on the episodic Q-learning with linear function approximation, for performance optimization; the second, based on the continuous Natural Policy Gradient REINFORCE algorithm, for performance recovery. Despite the simplicity of these approaches, we report satisfactory preliminary results, that represent the first step toward a new fully automatic procedure for the alignment of the seed laser to the electron beam. Such an alignment is, at present, performed manually.

Two diode lasers with different wavelengths resonantly pumped Er:YAG ceramic single-frequency laser

<p>Single-frequency solid-state lasers have important applications in laser remote sensing, such as Doppler lidar, differential absorption lidar (DIAL), gravitational wave detection and so on. In recent ten years, highly stable and narrow spectrum single-frequency Q-switched 1.6 μm lasers are widely applied in coherent Doppler wind detection liar and CH<sub>4</sub> DIAL. For applications in space-based wind lidar and DIAL, high output energy of the lasers is essential. In order to obtain a single-frequency laser with high energy, a common method is to inject a stable single-frequency seed laser into a high-energy Q-switched slave laser. Energy upconversion is the main factor which affects the energy enhancement of Er:YAG laser at 1.6μm. We report a Er:YAG ceramic single-frequency pulsed laser at 1645nm dual-end-pumped by two diode lasers with different wavelengths. Compared to a laser pumped by the two same wavelength diode lasers, the laser has higher slope efficiency because the energy upconversion is weakened. Otherwise, ceramic materials have many advantages compared with single crystals, such as ease of fabrication large-size ceramic material, short fabrication time, low cost and good thermo-mechanical properties. Uniform dopant can be realized in ceramic materials, which are much tougher and stronger than single crystals. All the advantages of ceramic materials mentioned above contribute to scalability to high energy laser. In this letter, we report a single frequency pulse ceramic laser with output energy of more than 10 mJ and pulse-width of more than 150 ns at a repetition rate of 500 Hz, which is pumped by two diode lasers with the wavelengths of 1470 nm and 1532 nm, respectively. This single-frequency pulse laser is a potential candidate as a seed laser for a slab laser amplifier system, which is an ideal source for space-based DIAL and Doppler wind lidar.</p>