A microwave phase-control scheme is proposed and experimentally demonstrated. Two lasers are combined in an optical fiber coupler to generate a beat signal. The beat frequency is tuned by controlling the frequency of one laser. Using the phase shift of the beat waves with different frequencies during the propagation in an optical fiber, the phase of the radio-frequency (RF) signal generated by a photodetector (PD) can be controlled. Using the phase shift during the propagation of beat waves in an optical fiber with different beat frequencies, the phase of the RF signal generated by a PD connected to the fiber can be controlled. A tunable phase shift ranging from 0 deg to 1400 deg is obtained for frequencies from 6 to 10 GHz. This scheme offers the advantages of fast tuning and precise phase control of an RF signal.
Optical systems made for space-based interferometric missions like LISA or SIM must be made of materials that can endure significant accelerations and temperature fluctuations while staying dimensionally stable. Temperature-induced effects can be reduced with thermal shielding techniques and estimated using the thermal expansion coefficient. However, the stability is often limited by virtually unquantified material internal relaxation processes. In this paper we describe the experimental layout and present the status of our experiments to measure the dimensional stability of Zerodur and Hexoloy SA<sup>®</sup> silicon carbide using hydroxide-bonding and discuss its feasibility for the LISA mission.
The Laser Interferometer Space Antenna (LISA) is a joint NASA/ESA space mission aimed to detect gravitational waves in the 3×10<sup>-5</sup> to 1Hz frequency range. Expected sources for LISA include super massive black hole mergers (SMBH), galactic neutron star and white dwarf binaries, and extreme mass ratio inspirals (EMRI). The three LISA spacecraft will travel in a heliocentric orbit trailing or leading earth by about 20°. The distance between the spacecraft will be about 5 million km or 16s light travel time. Laser interferometry will measure the distance with pm/√Hz accuracy. This report focuses on the technology for LISA interferometry.
In the advancing field of gravitational wave interferometry, the desire for greater sensitivity leads to higher laser powers to reduce shot noise. Current detectors such as LIGO and GEO 600 operate with continuous wave lasers at 10-15 W powers, however future versions will operate at 200 W. One of the major challenges of higher power operation is the creation of thermal lenses in optical components, caused by from the absorption of laser light, yielding optical path deformation and concomitant beam aberrations. This effect is especially problematic in transmissive optical components even at very low levels of absorbed power. In environments that restrict the ability to move optical components (such as gravitational wave detectors), this effect can be used for beneficial purposes, specifically for providing adjustable beam-shaping. The method employs an additional laser having a wavelength strongly absorbed by the substrate and can create an aberration-free parabolic lens can be created provided that the heating beam mode is
substantially larger than the transmitted beam mode. The resulting focal length varies inversely with the heating laser power. This idea forms the basis for an adaptive optical telescope. We present experimental and theoretical results on a laser adaptive mode-matching system that uses an argon laser absorbed in a color glass filter. We characterize the dynamic focal range of the lens and measure the resulting aberrations in the transmitted Nd:YAG beam. Our results are in good agreement with a theoretical model incorporating the temperature distribution of the lens and the relevant thermo-optic parameters.