LIGO Operations Annual Report from the LIGO Caltech 40 Meter Laboratory June 27, 2005 The 40-Meter Laboratory has been rebuilt in order to fully develop and test the optical configuration and control scheme for Advanced LIGO. We are currently very close to achieving our primary goal: to acquire lock and robustly control a power- and signal-recycled Michelson interferometer with Fabry-Perot arms, and demonstrate the expected response to gravitational waves. The optical configuration of the 40 meter interferometer mimics the one planned for Advanced LIGO: high finesse Fabry-Perot arms (1235, to be compared with the Initial LIGO arm finesse of 200); correspondingly reduced gain in the power recycling cavity (in order to reduce the thermal load on the transmissive optics in the presence of higher input laser power); a mirror at the asymmetric port of the beamsplitter in order to resonantly extract the GW sidebands from the high-finesse arm cavities and thereby increase the detection bandwidth; and a detuning of the signal extraction cavity in order to enhance sensitivity at a strategically-chosen range of frequencies. The more complex optical configuration makes it significantly more difficult to acquire full lock than for Initial LIGO, so it is essential to establish a well-defined, reliable, robust and automated procedure for lock acquisition with a full prototype such as the 40 meter interferometer. The 40 meter interferometer is now almost fully instrumented, with a full Initial-LIGO pre-stabilized laser, ten (single-pendulum) suspended optics with digital controllers and optical lever monitors, a 13-meter input mode cleaner, a data acquisition (DAQS) system, slow control and monitoring (EPICS) system, Global Diagnostics systems, fast (16 kHz) front-end servo controls, and a next-generation length sensing and control system. The more complex length sensing system involves multiple RF sidebands, applied within an input Mach-Zehnder interferometer. An alignment sensing system remains to be fully commissioned, but it is not necessary for lock acquisition. We are able to routinely acquire lock and control the interferometer in a variety of intermediate configurations, including the power-recycled Michelson with Fabry-Perot arm (PRFPMI, the Initial LIGO configuration) and the power- and signal-recycled (ie, dual-recycled) Michelson (DRMI) with blocked arms. The detuned signal cavity causes the usual RF signals to change radically, so adding the signal mirror to the Initial LIGO configuration is not straightforward. Our approach is the following: (a) lock the DRMI (with blocked arms) using RF signals from the beats between the carrier and sidebands; (b) transfer control to RF signals from the beats between the sidebands only, so that it will not be disturbed when the carrier resonates in the arms; (c) unblock and lock the carrier in the arms using the transmitted light, but offset from resonance (which is much easier than "catching" the RF signal from the narrow resonance in the high-finesse arm cavities); (d) transfer control of the differential arm signal (DARM) to RF, with zero offset; (e) reduce the offset in the common-mode arm signal (CARM) until the carrier is fully resonant in the arms, and transfer control to the RF signal with zero offset. We can routinely accomplish all these steps except for the last; at this stage, all five degrees of freedom are under control, but the offset-locked arms means that the neither resonant sideband extraction nor power recycling are in full effect (although we have observed both of these effects to a reduced extent). The last step is the most difficult one, because the cavity dynamics causes lock to be lost before the carrier is fully resonant in the arms. This problem can be overcome by using a dynamically changing CARM loop servo, which is currently under development and test. We are very close. Once lock is achieved in the full configuration, we will fully characterize the interferometer, including its power buildup, expected response to GWs, sensitivity, and noise budget. We will fully automate the lock acquisition, optimization, and characterization process. We will ensure that these procedures will be directly relevant for Advanced LIGO via detailed simulations of the dynamics of both the 40-Meter and Advanced LIGO interferometers. We are collaborating with the LIGO e2e group and the VIRGO Orsay group to develop a detailed time-domain model simulation of Advanced LIGO and 40-Meter interferometers. Because the Advanced LIGO optical design calls for a detuned signal cavity, RF sidebands will be unbalanced at all exit ports. This greatly increases the already serious problem of using noisy RF sidebands as the local oscillator for extracting the GW signal. Therefore, the Advanced LIGO design will employ a DC (homodyne) detection scheme, in which a controlled amount of filtered carrier light is allowed to exit the asymmetric port to serve as a less noisy local oscillator for GW detection at DC. We have developed a first-generation DC detection chain, including an in-vacuum output mode cleaner to strip all the RF sidebands and higher-order transverse modes from the output beam, and an in-vacuum DC photodiode. (Additional in-vacuum steering mirrors, mode matching telescope, beam diagnostics and readout and control systems are also required). We plan to implement and test this DC detection system at the 40 meter lab in the coming months. Further on, we are discussing the prospect of injecting squeezed vacuum into the asymmetric port of the interferometer, using a squeezing apparatus developed at the LIGO MIT quantum measurement group. This system holds the promise of reducing the quantum noise in GW detection over a range of frequencies. The 40-Meter team continues to work closely with the LIGO Controls group, the LIGO e2e simulation group, the LSC Advanced Interferometer Configurations subgroup, and LIGO Laboratory engineers and management. Graduate students, REU (Research Experiences for Undergraduates) summer students, visiting students, and visiting scientists have contributed to all aspects of the project over the last six years. In particular, REU students have made major contributions to design of the main interferometer optical plant and the length and alignment control systems, to the configuration and commissioning of the pre-stabilized laser, digital suspension controllers, suspended-mass input mode cleaner, and optical lever alignment sensing systems, and to the simulation of lock acquisition and dynamics of the dual-recycled interferometers with e2e. In the past year, the 40-Meter lab has hosted fruitful long-term visits from scientists from Japan, Perth and Canberra in Australia, Glasgow, Hamburg, and Orsay. We will continue to involve students and visitors with all aspects of the project and its goals. The laboratory continues to be a popular tour site for local students, journalists, scientific visitors, and dignitaries.