Schematic of the internal signal path on the FPGA. Insets denote parameters controlled by the user interface. SM: pictorial representation of the state machine that switches between lock and scan states (debug state not shown).
Screenshots of the user interface that controls the FPGA loop, scan, filter, and debugging parameters. Shown are the main lock panel (top left), the menu options (top right), the scan control panel (bottom left), the filter settings panel (bottom right), and the debugging panel (center right). Mouse clicks on the + and − buttons or key presses of the up arrow or down arrow keys smoothly change the currently active parameter. The order of magnitude of change depends on the digit that the cursor is positioned over.
Setup used to test performance of the locking circuit. Following the light path, the labels are DL: external-cavity diode laser, AL: aspheric lens, G: grating, P: piezo-electric transducer, L: spherical lens, OI: optical isolator, AO: accousto-optic modulator, H: half-wave plate, F: polarization-maintaining single-mode optical fiber, TA: tapered amplifier, CL: cylindrical lens, PPLN: periodically poled lithium-niobate waveguide crystal, CO: crystal oven, BF: bandpass filter, G: glass slide, RC: reference cavity, PD: photodiode.
Electromagnetically induced transparency to measure the linewidth of the locked laser. (a) Ladder-type excitation scheme (Rydberg-EIT). (b) Rydberg-EIT setup with counterpropagating probe and coupling beams. Labels are H: half-wave plate, PBS: polarizing beamsplitter cube, I: iris, VC: rubidium vapor cell, CM: cold mirror, PD: photodiode, AO: accousto-optic modulator.
EIT measurement. The probe transmission photodiode signal is plotted vs. the coupling laser detuning. The coupling laser frequency is swept by slowly ramping the reference cavity piezo voltage, while the ECDL is locked to the red side of the cavity peak. The EIT peak has a width of . This corresponds to a frequency range of for the ECDL light and gives an upper limit on the locked ECDL linewidth.
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