LIGO 40M IFO Pre-alignment Proceduresajw/40m/40M_IFO_Pre-alignment.pdf · 40M IFO Pre-alignment...

LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY

LIGO Laboratory / LIGO Scientific Collaboration

LIGO-T030141-00-D LIGO 7/17/03

40M IFO Pre-alignment Procedures

Michael R. Smith

Distribution of this document: LIGO Science Collaboration

This is an internal working note

of the LIGO Project.

California Institute of Technology LIGO Project – MS 18-34 1200 E. California Blvd.

Pasadena, CA 91125 Phone (626) 395-2129 Fax (626) 304-9834

E-mail: [email protected]

Massachusetts Institute of Technology LIGO Project – NW17-161

175 Albany St Cambridge, MA 02139 Phone (617) 253-4824 Fax (617) 253-7014

E-mail: [email protected]

LIGO Hanford Observatory P.O. Box 1970

Mail Stop S9-02 Richland WA 99352 Phone 509-372-8106 Fax 509-372-8137

LIGO Livingston Observatory

P.O. Box 940 Livingston, LA 70754

Phone 225-686-3100 Fax 225-686-7189

http://www.ligo.caltech.edu/

LIGO LIGO-T030141-00-D

Table of Contents

1 Introduction _______________________________________________________________ 4

1.1 Background ___________________________________________________________ 4

1.2 Scope ________________________________________________________________ 4

1.3 Auxiliary Alignment Equipment __________________________________________ 4

2 Alignment Procedures _______________________________________________________ 5

2.1 Michelson Version with Arm Cavities _____________________________________ 5 2.1.1 IO Pre-alignment into IMC____________________________________________ 5 2.1.2 Faraday Isolator ____________________________________________________ 6 2.1.3 IMCR Beam _______________________________________________________ 7 2.1.4 IMCT Beam _______________________________________________________ 7 2.1.5 ETMx ____________________________________________________________ 7 2.1.6 ITMx _____________________________________________________________ 8 2.1.7 IMMT ____________________________________________________________ 9 2.1.8 BS ______________________________________________________________ 10 2.1.9 ITMy and ETMy___________________________________________________ 11 2.1.10 Initial Pointing Beam _______________________________________________ 12 2.1.11 Antisymmetric Port Beam, AP1 _______________________________________ 12 2.1.12 Symmetric Port Beam, SPS __________________________________________ 12

Table of Figures Figure 1: IO input beam alignment .................................................................................................... 5 Figure 2: Faraday isolator alignment ................................................................................................ 6 Figure 3: ETMx chamber and ISC table ............................................................................................ 7 Figure 4: ITMx chamber..................................................................................................................... 8 Figure 5: Input chamber and BS chamber ......................................................................................... 9 Figure 6: ITMy chamber................................................................................................................... 10 Figure 7: ETMy chamber ................................................................................................................. 11

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Abstract

Procedures for pre-aligning the 40 M interferometer using an IR autocollimator are described.

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1 Introduction

1.1 Background The 40 M interferometer (IFO) consists of the following optical subsystems: the pre-stabilized laser (PSL), the input optics optical train (IO), which includes a Faraday isolator and an input mode matching telescope (IMMT), the input mode cleaner (IMC), and the main interferometer, which consists of a power recycling mirror (PRM), a beam splitter mirror (BS), input test masses (ITMx and ITMy), end test masses (ETMx and ETMy), and a signal recycling mirror (SRM). In addition to the main optical elements described above, there are a series of pickoff (PO) beams that are directed to external interferometer sensing and control (ISC) tables by means of auxiliary optics inside and outside the vacuum chambers.

In order to facilitate the final alignment of the interferometer, a pre-alignment procedure will be used to align the various mirrors and control beams within the active control range of the various actuators and steering optics.

1.2 Scope This document details the alignment procedures for pre-aligning two versions of the 40M IFO: (1) the initial Michelson version with Fabry Perot arms, but without any recycling mirrors, and (2) the final dual-recycled IFO.

1.3 Auxiliary Alignment Equipment The following items of auxiliary alignment equipment are required:

1. Model D-271 autocollimator, 4W 940nm illuminator with video display

2. autocollimator stand, 4.0 inch height

3. autocollimator stand, 5.5 inch height

4. Sony video camera with monitor

5. 4ea, iris diaphragm mounts and alignment targets with concentric aperture, 5.5 in height

6. power meter prepared for clean, in-chamber use

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2 Alignment Procedures

2.1 Michelson Version with Arm Cavities

2.1.1 IO Pre-alignment into IMC

This procedure will be done with the PSL laser at maximum power and with the polarization vector rotated parallel to the plane of the input optical table surface.

Place an iris diaphragm at 5.5 in height close after the first turning mirror on the output vacuum chamber optical table, where the PSL laser beam enters the vacuum chamber. Place a second iris diaphragm at 5.5 in height on the input vacuum chamber optical table close to the MC1 mirror of the input mode cleaner. See Figure 1.

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OUTPUT CHAMBER INPUT CHAMBER

IMCR

IMCT

IRIS MC3 MC1

Figure 1: IO input beam alignment

Align the two irises laterally to mark the horizontal direction of the IO beam into the IMC. Observe the 1064 nm laser beam with an infrared viewer, and adjust the height of the IO beam so that it passes through the center of both irises. The second iris mount will be left permanently in place with the iris removed to mark the center of the input beam to the IMC.

Re-align the three IMC mirrors, MC1, MC2, and MC3 so that transient locks of the mode cleaner cavity in air are observed.

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2.1.2 Faraday Isolator

This procedure will be done with the PSL laser at maximum power and with the polarization vector rotated parallel to the input optical table surface. The Faraday isolator is pre-aligned before installation for maximum throughput and extinction ratio.

Install the DLC turning mirror after MC3, and the IMCR pick-off beam-splitter (W2-1F-1525-C-1064-0).

Place an iris diaphragm at 5.5 in height close after the Faraday isolator. Without the Faraday isolator in place, align the DLC turning mirror after MC3 so that the IO beam passes freely through the iris and is observed with an IR viewer and a target. See Figure 2.

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IMMT

TARGET IRIS

FARADAY

MC3 MC1

Figure 2: Faraday isolator alignment

Place a power meter behind the iris. Install the Faraday isolator roughly iPlace a temporary ½ wave plate in front of the Faraday isolator. Rotate the

½ WAVE PLATE

n its aligned position. half-wave plate until

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maximum power transmission is obtained. Position the Faraday isolator laterally so that the beam passes freely through.

Remove the half-wave plate.

Leave the iris mount in place after the Faraday isolator for the subsequent alignment of the IO beam through the IMMT.

2.1.3 IMCR Beam

Adjust the lateral position and the angle of the DLC steering mirror so that the reflected PSL laser beam is projected through the window on the output chamber onto the AP ISC table, as viewed with an IR viewer. See Figure 1.

2.1.4 IMCT Beam

Temporarily replace the pick-off beam-splitter with an aluminized mirror. Adjust the lateral positions and the angles of the IMCR pick-off beam-splitter mount, and the DLC steering mirror so that the IMC transmitted beam is projected through the window on the output chamber onto the AP ISC table, as viewed with an IR viewer. See Figure 1.

Take out the aluminized mirror and replace it with the proper pick-off beam-splitter.

2.1.5 ETMx

2.1.5.1 Autocollimator alignment

Install the ETMx and the ITMx mirrors. Place a near iris diaphragm at 5.5 in height close to the output side of the ETMx on the output beam centerline, and place another far iris diaphragm at 5.5 in height near the ITMx inside the arm cavity on the centerline. See Figure 3 and Figure 4.

MC1 ETMX

AC

IRIS

Figure 3: ETMx chamber and ISC table

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IRIS

ITMX

Figure 4: ITMx chamber

Place an IR autocollimator projector at 4.0 in height on the ETMx ISC table. Place centering targets in both the near and far iris mounts. Project a focused reticle pattern onto the center of the near target at the ETMx mirror, as viewed with a Sony video camera. The reticle pattern is focused by turning the knurled barrel at the back end of the autocollimator. Remove the near target and project the focused reticle pattern through the iris mount onto the far target near the ITMx mirror. Iterate the procedure until the projected reticle pattern is aligned with the centers of both the near and far irises.

2.1.5.2 ETMx Alignment

Focus the autocollimator at infinity by placing the corner cube at the output of the autocollimator and rotating the knurled barrel until the observed retro-reflected reticle pattern in the video monitor is as sharp as possible. Note that there is considerable backlash in the knurled barrel, which requires that the focus always be approached from the same rotational direction.

Remove the corner cube and adjust the alignment of the ETMx until the center dot of the reflected reticle pattern from the HR surface is centered with the cross hairs of the eyepiece, as observed in the video monitor. Note that retro-reflections will be observed from both the HR and AR surfaces of the ETM mirror, and care must be taken to insure that the reflection used for alignment is from the HR surface. Record the pitch and yaw settings that correspond to the correct alignment.

Remove both the near and far iris diaphragm mounts. This completes the alignment of ETMx.

2.1.6 ITMx

Purposely misalign the ETMx mirror in yaw by using a wrong yaw setting so that the reflected reticle patterns from the ETMx HR and the ETMx AR surfaces are out of the field-of-view of the

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autocollimator. If there is not enough range in the mirror controller, use the earthquake stops to misalign the ETMx mirror.

Adjust the alignment of the ITMx until the center dot of the reflected reticle pattern from the HR surface is centered with the cross hairs of the eyepiece, as observed in the video monitor. Note that retro-reflections will be observed from both the HR and AR surfaces of the ITM mirror, and care must be taken to insure that the reflection used for alignment is from the HR surface. Record the pitch and yaw settings that correspond to the correct alignment.

Restore the ETMx mirror to its aligned condition and re-check the alignment of the aucotollimator. If the alignment of the autocollimator has changed, repeat the alignment of ITMx. Otherwise, this completes the alignment of ITMx.

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PZT IMMT

PZT

INI PICK-OFF

BS

Figure 5: Input chamber and BS chamber

2.1.7 IMMT

Install the BS mirror. Install the IMMT, the two PZT steering mirrors, and the initial pointing beam pick-off (LW-2-2050-C-1064-45P, note: the narrow part of the wedged mirror should lie in the horizontal plane pointing toward the center of the BS chamber) before the PRM. Place an iris diaphragm at 5.5 in height close to the output of the IMMT. See Figure 5 (do not install the autocollimator until paragraph 2.1.8 below).

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Adjust the lateral positions and the angles of the two turning mirrors and the two PZT steering mirrors so that the focused reticle pattern is projected onto the center of the target at the output of the IMMT, as viewed with a Sony video camera.

Adjust the position and orientation of the IMMT so that the focused reticle pattern is projected through the iris at the output of the IMMT, through the IMMT, and onto the center of the target before the turning mirror into the IMMT. It may be necessary to iterate the alignment of the DLC turning mirror and the first PZT steering mirror after the IMMT.

Place a target screen near the input to the Faraday isolator. Rotate the fixed turning mirror before the IMMT to observe the free passage of the center of the reticle pattern through the center of the Faraday isolator. It may be necessary to iterate the pitch alignment of the DLC turning mirror and the first PZT steering mirror after the IMMT.

This completes the alignment of the IO optical train.

2.1.8 BS

Install the ITMy and the ETMy mirrors. See Figure 6 and Figure 7. Place the projection autocollimator on the BS chamber table at 5.5 in height in front of the fixed turning mirror leading to the 2nd PZT steering mirror, shown in Figure 5. Note: a counterweight must be placed opposite the autocollimator to maintain the table level. Place a near iris diaphragm at 5.5 in height close to the input side of the ITMy on the centerline, and place another far iris diaphragm inside the arm cavity on the centerline near the ETMy.

ITMY

IRIS

Figure 6: ITMy chamber

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IRIS

ETMY

Figure 7: ETMy chamber

Adjust the pointing angle of the autocollimator perpendicular to ITMx so that the center dot of the reflected reticle pattern from the HR surface of the ITMx is centered with the cross hairs of the eyepiece, as observed in the video monitor. Purposely misalign the ITMx mirror in yaw so that the reflected reticle patterns from the ITMx are out of the field-of-view of the autocollimator.

Adjust the lateral position and the angle of the BS mirror so that the focused reticle pattern is projected onto the center of the near target at the ITMy mirror, as viewed with a Sony video camera. Remove the near target and project the focused reticle pattern through the iris mount onto the far target near the ETMy mirror. Iterate the procedure until the projected reticle pattern is aligned with the centers of both the near and far irises.

This completes the alignment of the BS.

2.1.9 ITMy and ETMy

Adjust the alignment of the ITMy until the center dot of the reflected reticle pattern from the HR surface is centered with the cross hairs of the eyepiece, as observed in the video monitor. Then purposely misalign the ITMy mirror in yaw so that the reflected reticle patterns are out of the field-of-view of the autocollimator.

Adjust the alignment of the ETMy until the center dot of the reflected reticle pattern from the HR surface is centered with the cross hairs of the eyepiece, as observed in the video monitor.

Remove both the near and far iris diaphragm mounts. Restore the ITMy to its proper alignment. This completes the alignment of the ITMy and the ETMy.

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2.1.10 Initial Pointing Beam

Install the initial pointing beam splitter, the fixed turning mirrors, and the DLC steering mirrors for the initial pointing position beam and for the initial pointing angle beam. See Figure 5.

2.1.10.1 Initial Pointing Beam, Position

Adjust the lateral positions and the angles of the fixed turning mirror and the DLC steering mirrors in the BS chamber so that the focused reticle pattern is projected through the chamber window onto the BS ISC table, as viewed with a Sony video camera.

2.1.10.2 Initial Pointing Beam, Angle

Adjust the lateral positions and the angles of the initial pointing beam beamsplitter DLC mirror mount in the BS chamber and the fixed turning mirror and DLC steering mirror in the ETMy chamber so that the focused reticle pattern is projected through the chamber window onto the ETMy ISC table, as viewed with a Sony video camera.

2.1.11 Antisymmetric Port Beam, AP1

Adjust the lateral positions and the angles of the fixed steering mirror and the two DLC steering mirrors in the AP1 optical train so that the focused reticle pattern is projected past the IMMT and through the chamber window on the input chamber onto the AP ISC table, as viewed with a Sony video camera.

2.1.12 Symmetric Port Beam, SPS

Adjust the lateral positions and the angles of the Brewster mirror and the DLC steering mirror in the SPS optical train so that the focused reticle pattern is projected through the chamber window on the input chamber onto the AP ISC table, as viewed with a Sony video camera.

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