PO Beam Waist Size and Location on the ISC Table

Transcription

1 LASER INTERFEROMETER GRAVITATIONAL WAVE OBSERVATORY - LIGO - CALIFORNIA INSTITUTE OF TECHNOLOGY MASSACHUSETTS INSTITUTE OF TECHNOLOGY Document Type LIGO-T D 8/4/98 PO Beam Waist Sie and Location on the ISC Table Michael Smith Distribution of this draft: Table of Contents Index California Institute of Technology LIGO Project - MS 5-33 Pasadena CA 95 Phone (66) Fax (66) info@ligo.caltech.edu This is an internal working note of the LIGO Project. WWW: Massachusetts Institute of Technology LIGO Project - MS 0B-45 Cambridge, MA 039 Phone (67) Fax (67) info@ligo.mit.edu file H:\COS\ISC_tel_out.fm - printed August 4, 998

2 LIGO-T OVERVIEW The PO beam waist location on the ISC table can be varied by defocusing the ISC telescope. An optical schematic drawing of the PO beam optical train, which includes the 8X reflective telescope inside the vacuum housing and the 3.3X ISC telescope on the ISC optical table is shown in The input beam waist is inside the IFO, approximately 900 m from the PO telescope. The ISC telescope is separated from the PO telescope by approximately 3 m. The input beam waist is transformed by the lens train to an output beam waist of sie w 04, located in the vicinity of the ISC table at a distance 4 from the end of the ISC telescope. f +f d f 3 +f 4 + ISC w 0 w 0 w 03 w 04 w 04 L 3 L 4 L L 3X ISC telescope 8X PO telescope ISC Table Figure : Optical schematic of PO beam optical train The sie and location of the output beam waist can be determined by using Gaussian beam transformation theory. GAUSSIAN BEAM TRANSFORMATION THEORY An analysis of the dependence of the output beam waist and location on the defocusing of the ISC telescope was made using the following parameters.. Telescope Parameters PO Telescope primary focal length, f secondary focal length, f 54 mm mm page of 9

3 LIGO-T input beam waist position, input beam waist parameter, w 0 distance to ISC telescope, d ISC Telescope primary focal length, f 3 secondary focal length, f mm 36.4 mm 3000mm 58 mm mm.. Gaussian Beam Transformation Equations f f f. f π w 0. f w 0 w 0 w 0 f 0.5 w 0 w 0 f f f f f. w 0 f f w 0 w 0 w 0 f 0.5 page 3 of 9

4 LIGO-T w 03 w 0 3 d 3 f 3 f. 3 3 f 3 3 f 3 w 03 3 f 3 w 03 w 03 w 03 f w 04 w 03 4 ISC f 3 f 4 ISC 3 4 ISC f 4 ISC f 4 f ISC f 4 π w ISC f 4 w 04 ISC w 04 w 04 f 4 Raleigh range of ISC output, mm R ISC w 04 ISC 0.5 page 4 of 9

5 LIGO-T Results: Output Beam Waist Sie and Location The location of the ISC telescope output beam waist, as measured from the output lens, can be varied by defocusing the ISC telescope as shown in figure. The Rayleigh range associated with the output beam waist is also shown in figure. The output beam waist sie varies as the telescope is defocused, as shown in figure 3. The actual spot sie at the output of the ISC telescope is also plotted in figure 3. Beam waist position, and Rayleigh range, mm 4 ISC R ISC Rayleigh range beam waist position ISC Defocus, mm Figure : Beam waist position and Raleigh range versus ISC defocus, d=3000mm page 5 of 9

6 LIGO-T Gaussian beam radius, mm w 04 ISC w ISC 4 3 output spot sie beam waist sie ISC Defocus, mm Figure 3: Beam waist sie versus ISC defocus, d=3000mm.3. Locating the Far Field of the ISC Telescope It is desirable to minimie the effect of the position of the ISC telescope on the Guoy phase at the WFS detector, by placing the first Guoy lens of the WFS system in the far field of the ISC telescope output. This can be accomplished by defocusing the ISC telescope approximately -0.6 mm, which will place the apparent output beam waist at the location mm (refer to figure ). And since the Rayleigh range is mm, the output beam will be in the far field as it emerges from the ISC telescope. 3 ISC TELESCOPE DESIGN DETAILS 3. Optical Design Specification The optical design specification for the ISC telescope is shown in the optical schematic of figure 4. It will incorporate stock lenses, with AR coatings for 064 nm wavelength, as specified page 6 of 9

7 LIGO-T Mechanical Characteristics objective lens: part number nominal focal length diameter clear aperture center thickness edge thickness material Figure 4: ISC Telescope, optical schematic Edmund Scientific, p/n D mm mm 3 mm 7.5 mm 6.75 mm BK7/SF5 page 7 of 9

8 LIGO-T eyepiece lens: part number nominal focal length diameter clear aperture center thickness edge thickness material Edmund Scientific, p/n D mm mm 3 mm.5 mm 4.93 mm UV grade fused silica 3.3. Clear Aperture and Field of View Requirements The COS ISC telescope was designed with an optical axis displacement tolerance of +/- 8 mm, and a field-of-view tolerance of +/- 4x0^-4 rad. The total position shift and angular error in the COS pick off beam at the ISC table due to initial COC alignment errors, pump-down shifts, and long term stack drifts are estimated to be +/- 3 mm and 4x0^-3 rad; which exceed the design requirements of the ISC telescope. Therefore it will be necessary to direct the beam into the ISC telescope commensurate with the clear aperture and field-of-view design constraints. (See COS PDR sec , and Table 3) Mounting Configuration The ISC telescope lenses will be mounted in a simple focus tube configuration, as shown in figure 5. The focus tube must have a range of adjustment of -0.6 mm in order to place the output of the telescope in the far field, as described previously. See Locating the Far Field of the ISC Telescope on page 6. The telescope tube can be mounted to the ISC table with a standard tube mount fastened to an optical post, as shown. page 8 of 9

9 LIGO-T Dampened Rod Purchase Parts Adjustable Focus Tube - 40 UNS Thd. Approx Dia. ISC Telescope Full Sie ISC Telescope Figure 5: Mounting configuration, outline drawing for ISC telescope page 9 of 9