ABSTRACT
We present and characterize a narrow-linewidth external-cavity diode laser at 2â µm, and show that it represents a low-cost, high-performance alternative to fiber lasers for research into 2â µm photonic technologies for next-generation gravitational-wave detectors. A linewidth of 20 kHz for a 10 ms integration time was measured without any active stabilization, with frequency noise of â¼ 15 Hz/Hz between 3 kHz and 100 kHz. This performance is suitable for the generation of quantum squeezed light, and we measure intensity noise comparable to that of master oscillators used in current gravitational wave interferometers. The laser wavelength is tunable over a 120 nm range, and both the frequency and intensity can be modulated at up to 10 MHz by modulating the diode current. These features also make it suitable for other emerging applications in the 2â µm wavelength region including gas sensing, optical communications and LIDAR.