193-mHz beat linewidth of frequency-stabilized laser-diode-pumped Nd:YAG ring lasers

Laser frequency locking with second-harmonic demodulation

An external-optical-cavity-based laser frequency-locking method with second-harmonic demodulation was proposed, analyzed, and demonstrated. The second-harmonic component of the cavity output was demodulated to feed back to the frequency-locking loop, resulting in a high sensitivity, great carrier suppression, and large modulation bandwidth. The experimental demodulation curve was consistent with the simulation result. A distributed feedback fiber laser was then locked using this technique. A carrier wave suppression ratio of -67  dB and a laser frequency noise floor of 1  Hz/Hz level above 1 Hz were achieved. This technique has great potential to be used in resonator optic gyroscopes.

High-bandwidth laser frequency stabilization to a fiber-optic delay line

Stabilization of laser frequency to interferometers with a large time delay in one arm is of significant interest to space-based gravitational wave detectors such as the Laser Interferometer Space Antenna. A recently proposed technique allows a control bandwidth larger than the inverse delay time to be achieved. We present experimental results demonstrating laser frequency stabilization to an optical fiber delay line. A control bandwidth approximately 50 times the inverse delay time is demonstrated.

Near shot-noise-level relative frequency stabilization of a laser-diode-pumped Nd:YVO(4) microchip laser

A laser-diode-pumped Nd:YVO(4) microchip laser was built and actively frequency stabilized relative to a Fabry-Perot cavity with the frequency-modulated sideband technique. The error signal reaches the shot-noise level of 7.4 mHz/√Hz around 1 kHz. Excess intensity noise sets a lower limit of16.5 mHz/√Hz for the relative frequency noise, corresponding to a spectral linewidth of 860 μHz. We discuss the method for reconstructing the actual frequency deviation from the observed error signal.

Ultralow-loss mirror of the parts-in-10(6) level at 1064 nm

We describe an ultralow-loss and high-reflectance mirror at 1064 nm. A Fabry-Perot cavity is fabricated with two mirrors to measure the finesse and the transmission efficiency on resonance. The finesse was cross checked by two different methods: measurements of the cavity decay time and of the frequency-response function. As a result, a loss of 6 +/- 6 x 10(-6) (6 +/- 6 parts in 10(6), scatter and absorption) and a finesse of 2236 +/- 54 were measured during the cavity decay time. This result coincides with that of the response function within accuracies cited above. To our knowledge, the loss is the lowest obtained at 1064 nm.

Vibration transducer using an ultrashort Fabry-Perot cavity

We report here on the development of an optical transducer for mechanical vibration, making use of an ultrashort Fabry-Perot cavity. The noise level measured by a cavity 150 µm long is ~1.3 × 10(-16) m/√Hz at ~1 kHz, which was obtained without a frequency-stabilization system. It was, however, large compared with the shot noise.

Absolute frequency stability of a diode-laser-pumped Nd:YAG laser stabilized to a high-finesse optical cavity

We report the frequency stabilization of a diode-laser-pumped monolithic ring Nd:YAG laser locked to a high-finesse optical cavity. With an independent cavity as a frequency discriminator, the absolute frequency noise was measured to be as low as 2 × 10(-2) Hz/Hz(1/2) at the Fourier frequency of approximately 3 kHz. We also measured the heterodyne beat note between two lasers locked to the independent cavities. The beat linewidth is narrower than 30 Hz and the minimum root Allan variance is approximately 6 × 10(-14).

Ultrahigh-frequency stabilization of a diode-pumped Nd:YAG laser with a high-power-acceptance photodetector

We describe the ultrahigh-frequency stabilization of a diode-pumped Nd:YAG laser by use of a high-poweracceptance photodetector. The photodetector, which is constructed with an optical power divider and eight combined photodiodes, is developed to reduce shot-noise-limited FM noise. The laser frequency is locked to a Fabry-Perot cavity with a finesse of 25,600 by the Drever-Hall technique. By using the optical power of 47 mW at the photodetector, we reduce the relative FM noise at the error signal to the shot-noise limit of 4.2x10(-5) Hz/ radicalHz below the Fourier frequency of 500 Hz.