Research Projects

Butterfly LD Enclosure Assembly
Butterfly LD Enclosure Assembly

Temperature-Stabilized Diode Laser Enclosure

We designed a temperature-stabilized enclosure for diode lasers to suppress thermal fluctuations and increase their resilience for field applications.

    • Narrow linewidth DFB lasers at 780 nm are suitable for addressing transitions in rubidium, but their frequency is highly sensitive to current and temperature fluctuations.

    • Typical semiconductor diode current sensitivity of 3 pm/mA requires a low-noise controller. In our laser systems, we use Koheron laser diode contollers (CTL-101), which offer low current-noise densities of 110 pA/√Hz. However, because the laser’s temperature sensitivity is 60 pm/K, even a 0.002°C fluctuation will shift its optical frequency by approximately 6 MHz (one atomic linewidth).

    • Although the butterfly package includes an internal thermoelectric cooler and thermistor, residual thermal gradients make additional environmental stabilization necessary.

    • A compact, single-layer aluminum enclosure was therefore developed to house both the laser and its controller, minimize electrical connection lengths, and improve thermal conduction. The system uses two active temperature-control loops: an internal loop that tunes the laser frequency and an external loop that stabilizes the enclosure near 20°C.

    • Testing under external heating showed that the enclosure TEC reduced the laser baseplate temperature increase from 1.9°C to 0.2°C when exposed to >30°C for 5 minutes. This substantially improves the laser’s stability and resilience to environmental fluctuations.

Frequency Locking Circuit
Frequency Locking Circuit

Frequency-Offset Locked Laser Systems

We developed fast analog electronics for tuning diode lasers over several GHz using a frequency-offset locking scheme.

    • We developed a standalone, low-noise optical frequency-offset locking system that enables agile, high-precision control of narrow-linewidth lasers using only commercially available electronic components.

    • The work is motivated by the need for robust and cost-effective laser frequency control in atomic physics experiments, where conventional optical phase-locked loops often require expensive electro-optic components, ultra-stable local oscillators, and high-bandwidth electronics that increase system complexity and limit portability. Many applications—including laser cooling, atom interferometry, and quantum sensing—require excellent frequency stability but do not demand full optical phase coherence, creating an opportunity for a simpler locking architecture.

    • The system locks two follower lasers to a primary reference laser by measuring their optical beat note, dividing the radio-frequency signal, converting it to a voltage with a frequency-to-voltage converter, and applying feedback through a proportional–integral controller.

    • Its modular printed circuit board architecture provides a large tunable capture range exceeding 1 GHz, millisecond-scale response times, excellent linearity, and a frequency resolution of 1.9 kHz at 780 nm, without requiring expensive active photonic components or complex digital electronics.

    • The system was validated through high-resolution spectroscopy of laser-cooled 87Rb atoms, demonstrating accurate frequency tuning, robust suppression of laser frequency noise, and dynamic control suitable for laser cooling, atom interferometry, atomic clocks, and other quantum sensing applications.

Laser Locking Techniques with an Electro-Optic Modulator

We investigated frequency-modulation spectroscopy and modulation transfer spectrocopy for laser frequency stabilization.

    • Laser-frequency stabilization is essential in atomic physics applications such as spectroscopy, interferometry, atomic clocks, and laser cooling.

    • Effective laser cooling requires the laser frequency to remain within the narrow 5–10 MHz linewidth of an atomic transition so that repeated photon interactions can slow atoms from hundreds of metres per second to only a few millimetres per second.

    • Laser locking typically involves producing an atomic absorption spectrum, demodulating it to generate an error signal, and feeding that signal into a PID controller that corrects the laser frequency. Conventional methods directly modulate the laser at approximately 5 MHz to create useful sidebands, but this also broadens its effective linewidth.

    • This study investigates the use of an electro-optic modulator to generate the required modulation without directly broadening the laser and demonstrates how optimizing experimental parameters can improve the error signal and overall frequency lock.

Cold Atom Capture GUI

We developed a Python-based graphical user interface to record images of cold atoms and analyze their time-of-flight trajectory.

    • The Cold Atom Capture GUI is a PyQt-based application developed to automate the acquisition and analysis of cold atom cloud images for measuring atomic temperature and gravitational acceleration using time-of-flight techniques.

    • Designed as an extensible platform for future development, the software integrates with a FLIR Blackfly S camera to asynchronously capture images, processes 16-bit grayscale images using OpenCV, automatically identifies the atom cloud through statistical image analysis, and performs Gaussian fitting with the lmfit library to extract cloud position and size.

    • The GUI provides both live acquisition and offline analysis modes, allowing users to configure experimental parameters, adjust regions of interest, visualize images and Gaussian fits in real time, and review processed results.

    • The application was validated using a Gaussian laser spot before integration with the cold atom apparatus and is designed to interface directly with the laboratory's ARTIQ control system, enabling automated image capture synchronized with experimental sequences.

Lock-In Error Signal
Lock-In Error Signal

Laser Locking using an Analog Lock-In Amplifier

We designed a laser locking circuit capable of demodulating signals up to 2 MHz using an analog lock-in amplifier.

    • This lock-in amplifier project focused on developing a compact, all-in-one analog “laser lock box” to replace a commercial lock-in amplifier based on a digital signal processor that is limited to 100 kHz modulation frequency.

    • The system integrates high-pass and low-pass filters, variable-gain conditioning amplifiers, a high-speed lock-in amplifier (AD630), a proportional–integral–integral (PII) controller, and a summing amplifier into a single unit that generates an error signal from saturated absorption spectroscopy.

    • This error signal feeds back to the diode laser current to stabilize the laser on a selected rubidium absorption feature.

    • By eliminating the digital processing delay present in the commercial instrument, the new analog design aligns the error signal's zero crossing with the atomic transition, improving locking accuracy and response.

    • The project included the design, assembly, testing, and integration of each subsystem, demonstration of successful laser locking, and identification of future improvements.

RF Synthesizer
RF Synthesizer

Ultra-Low Phase Noise Microwave Synthesizer

We developed a dual-output microwave synthesizer at 6.6 GHz and 6.8 GHz for laser cooling rubidium-87 atoms and inducing transitions between hyperfine ground states.

RF Synthesizer Output

    • Ultra-low phase noise microwave synthesizers are critical for achieving high-precision quantum sensors based on cold-atom interferometry. Our synthesizer is designed for both laser cooling 87Rb atoms and inducing ground state Raman transitions that function as the atom-optical pulses in our interferometer.

    • During these pulses, the phase of the Raman laser is directly imprinted on the atomic wavefunction. Thus, for sensitive quantum measurements, a very low noise is desired for the microwave signal phase that is transferred to the atoms.

    • Our synthesizer design generates two independent microwave signals: one at 6.6 GHz that acts as a repump frequency for laser cooling, and one at 6.834 GHz — the hyperfine splitting in rubidium.

    • Both signals are derived from an ultra-stable 100 MHz ovenized crystal oscillator and a phase-locked dielectric resonator oscillator operating at 3.35 GHz.

    • The two microwave signals are combined and sent to an electro-optic phase modulator to generate the desired optical frequencies in our 780 nm laser system.

    • Preliminary measurements of the microwave power spectral density at 6.7 GHz yield a phase noise of −85 dB·rad²/Hz at an offset of 10 Hz. For a Mach-Zehnder type atom interferometer with a free fall time of T = 100 ms, we estimate a root mean squared phase noise of 135 mrad—corresponding to less than 1E-9 g per shot in a quantum gravimeter.

Cold atom source
Cold atom source

Ultracold Atom Source

We are constructing an ultracold source of rubidium-87 atoms for a high-accuracy quantum gravimeter.

    • Ultracold atoms are ideal for high-accuracy inertial sensing using atom interferometry.

    • The dominant systematic effect in atom interferometers using thermal clouds is due to the expansion of the atoms in the excitation beam (i.e. wavefront distortion). Cooling atoms to sub-recoil temperatures can dramatically reduce this effect.

    • We use a multi-stage cooling process involving a 2D+ magneto-optical trap (MOT), a 3D MOT, and an off-resonant optical dipole trap (ODT).

    • A compact quartz cell with an integrated rubidium dispensor facilitates the production of a cold atomic beam using a 2D+ geometry with custom-designed magneto-optical hardware capable of fast magnetic field switching.

    • The atomic beam loads a 3D MOT in a titanium science chamber with lower background pressure—ensuring extended trap lifetimes and interrogation times.

    • After an initial cooling and compression stage in the 3D MOT, the atoms are loaded into an ODT where their temperature is further reduced using evaporative cooling in a painted optical potential.

Science chamber

Non-magnetic UHV system for quantum sensing.

Vectorial Quantum Sensing Platform

We are constructing a vectorial quantum sensing platform to develop a new class of multi-axis atom interferometry. This platform is designed to provide high-accuracy measurements of local time (i.e., an atomic clock), and vector quantities such as acceleration, rotation rate, and magnetic field.

Most cold-atom-based sensors can measure only single components of 3D vector quantities like acceleration. Our architecture utilizes three mutually-orthogonal lasers—providing full vector sensitivity in a single device. This vectorial quantum sensor will require a new type of “atom optic” involving multidimensional atomic diffraction. This will enable new 2D and 3D geometries of matter-wave interferometers that are sensitive to all components of the acceleration and rotation vectors—providing a full inertial base for positioning and navigation applications. The same beam geometry can be harnessed to measure the full magnetic field vector. Finally, accurate measurements of local time can be realized a Ramsey-type atomic clock in a fountain geometry. Combining these capabilities in a single compact device would form the basis of a unique multifunctional instrument with several applications. For instance, the intrinsically 3D nature of this architecture opens new possibilities for ultra-high accuracy atomic gyroscopes—making it directly applicable to geophysicists in rotational seismology, and several civilian, military, and space industries utilizing state-of-the-art inertial navigation systems.