Optical Levers

Related subgroups: VIS, IOO, MIF, VAC, CRY...

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Scope

The scope of optical levers is to sense local angular motions (pitch and yaw) of any mirrors supported by vibration isolation system and other suspended stuffs including suspeded optical benches.

Applicable Documents

TBD; just see the links below.

General Description

Naming Conventions

TBD

Locations

• BS chamber
• ITM chambers (X,Y)
• ETM chambers (X,Y)
• PRC chambers (PRC, PR2, PR3)
• SRC chambers (SRC, SR2, SR3)
• MC chambers (MC1, MC2...)

Requirements

• Sensor noise should be less than xxx.
• Sensor's dynamic range should be greater than xxx.
• At least horizontal degrees of freedom (X,Y)
• Preferably a vertical sensor (Z) and side
• The sensors have to be rigidly mounted on the ground so that these are useful for remembering the position of the mirror and recording the drifts.

Characteristics

Each optical lever consists of an optical system, a frontend circuit, and a human interface software. The optical system consists of the following parts: a light source, optical fibers, a focusing telescope, viewport windows, a detector, and pylons which support the focusing telescope and the detector. The frontend circuit is TBD. Maybe we need analog cables (and what kind of connector should we use?), whitening filters and antialiasing filters. Maybe the matrix circuit will be realized using the digital systems, but in commissioning phase, we will need analog matrix. The human interface software is TBD, which shows the mirrors' dofs monitored by Optical Levers.

Light source

For the light source, proposed candidates are

• superluminous LED (SLED) or
• laser light source as LIGO.

Optical Fibers

The optical fibers transmit the light from the source to the focusing telescope.

Focusing Telescopes

TBD. Moving linear stage with micrometer and some optical components like collimators?

Viewport windows

See also the viewport subsystem. It should be transparent for the light source wavelength. There should be no wedge; otherwise the multiple spots of light would be problematic.

See JGW-T1201231, Effect due to viewports for optical lever (in Japanese)

Detectors

The detector will be an ordinary quadruplet photocondutive circuit with QPD. The noise level at xxx Hz should be xxx m/Hz²

Pylons

The pylons must be designed.

Inspection plans

TBD

Procurement process and plans

TBD

Links

Some of the LIGO documents listed below are NOT public; to access them, you may need your own LSC account.

• LIGO-M1000343, Advanced LIGO Review Committee Report: Test Mass Optical Lever FDR

• LIGO-T1000517, Optical levers Final Design Review for test masses, recycler mirrors and HAM optical benches

• LIGO-G1100961, Long-Term Stability Test for aLIGO Optical Levers

• JGW-­G1100418, LCGT vacuum chamber envelope study

• LIGO-T1000533, Super-luminescent LED 21 and 50 day trend analysis

• LIGO-T1000390, Trade-off Study for the Optical Lever Light Source

• LIGO-T1000219, Test mass optical levers preliminary design