Schematic of the laser diode assembly. (a) Complete assembly in hermetic enclosure. (b) and (c) Top and side-views, respectively, of the diode mount assembly. Diode is mounted on baseplate which is thermally coupled to Peltier cooling stacks. Slits in baseplate and grating mount provide vertical and horizontal flexure adjustment under tension from micrometer screws. Grating is mounted in Littrow configuration to reflect the first-order diffracted light directly back into diode chip, indicated by red-dashed line. A similar ECDL assembly has been successfully used to operate cryogenically cooled 780 nm diodes, pulled to 767 nm for laser cooling of neutral K. It has also been used for high-temperature operation of 660 nm diodes near 670 nm for laser cooling of Li. 32
Characterization of the output wavelength of the ECDL. (a) Temperature dependence of ECDL emission wavelength. LD is operating at 64 mW and grating is tuned to 626.266 nm. Black: emission wavelength measured by a high-finesse wavemeter. Measurements taken as temperature falls (right-to-left). Target wavelengths near 626 nm identified on the figure. (b) Sub-Doppler iodine features near 626.266 nm obtained using frequency-modulated lock-in-detection and polarization spectroscopy on an iodine vapour cell. Data were recorded from an oscilloscope monitoring the error signal generated using frequency-modulated lock-in-detection of the the iodine features while scanning the piezo at ∼10 Hz. Wavelength was calibrated using direct measurements of feature location via the wavemeter. Approximately 5–10 mW of optical power was used for iodine spectroscopy.
Injection locking in a master-slave configuration. (a) Schematic of the injection locking beamline. The master light is focused with a 150 mm lens to pass through the aperture of an optical isolator (Thorlabs IO-3-633-LP) from which it emerges with a +45° rotated polarization. This passes through a half wave plate (HWP) which restores the polarization to vertical, before being recollimated by a second lens and injected into the polarizing beamsplitter output of a second isolator (Thorlabs IO-5-633-PBS). The reflected light provides the optical feedback to the slave laser. A small reflected component from the first HWP is used for analysis. (b) Characterization of optical output from the slave laser for different injected powers. The size of a single optical mode measured using a Fabry-Perot spectrum analyzer grows linearly with slave output power until the injection power is insufficient to maintain single mode injection locking.
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