Laser injection locking of lithium diodes. An experimental approach with a 660 nm thorlabs diode and a 675 nm Ushio laser diode (PDF)

Bachelor Thesis from the year 2021 in the subject Physics - Applied physics, grade: 1,0, University of Tubingen, language: English, abstract: The goal of this work is to find a stable injection lock setup with over 100 mW of output power. There are two diodes characterized for this aim while injection locking them. One is available at Thorlabs with a center wavelength of 660 nm and up to 120 mW of output power in the free-running state. The other diode manufactured by Ushio is not yet readily available on the market but has a center wavelength of 675 nm with up to 0,25 W of output power and can be directly operated at 671 nm by lowering the temperature. There are concerns that this temperature would be below the dew point, especially in summer.

This causes condensation on the diode from the water vapor in the air, explaining why this diode is tested only via the second approach. In Section 2 a short introduction into semiconductor laser physics is explaining the working principle of laser diodes. Additionally, the injection locking theory and the Gaussian beam model are discussed. The experimental setup and instrument control are described in Section 3. This is followed by the characterization of the Thorlabs diode with a center wavelength of 660 nm in Section 4 and the Ushio diode with a center wavelength of 675 nm at appropriate temperatures in Section 5. An outlook on further improving the setup by actively stabilizing the injection lock is given in Section 6. In cold atom experiments for laser cooling and trapping of atoms, laser powers of more than 100 mW are often required.

Furthermore, magneto-optical traps, while loading, are in need of sufficient power to reduce the number of atoms lost on the way. The output power of an external cavity diode laser does not produce enough output power for such applications. Alternatively, tapered amplifiers are a way to produce sufficient output power. These are currently not available for the targeted laser cooling wavelength for lithium of 671nm. However, injection locking of free-running, high power diodes is an alternative to tapered amplifiers for delivering enough output power. This is a technique to produce higher output power at a stable frequency. To achieve this, a weak signal of typically a few mW of an external cavity diode "seed" laser is injected into a free-running "slave" diode, which is capable of higher output power.