Summary
New laser source installed and aligned with 60mm focal length collimating lens. Output beam looks single mode. ETMY imaged onto HWS and magnification calibrated to 22.8x using 4 measurements in three different techniques.
Adjusting beam from fiber
75mm focal length lens
We started work this morning with the 75mm focal length lens installed and the return beam from ETMY nominally imaged onto the HWS. (We deadreckoned the imaging by adjusting the pitch of the ETMY, looking at how much the aperture in the HWS image moved vertically and how sharp the image looked and then adjusting the longitudinal location of the HWS to maximize sharpness and minimize motion in response to an ETMY pitch - the HWS moved approximately 170mm closer to the laser mirror in the system).
This is the ETMY HWS return beam with the 75mm focal length lens.
I felt like there was still a lot of clipping so I wanted to try a smaller beam using a shorter focal length lens to collimate the source.
60mm focal length lens
We installed the 60mm focal length lens to collimate the HWS source laser.
1. Firstly, we sent the output beam into the beam scan and adjusted the relative positions of the fiber output and the collimating lens to get the Gaussian intensity distribution centered in the aperture of the lens - as shown below.
2. Next we adjusted the longitudinal position of the collimating lens until the beam was focussed to a point approximately 40mm past the lens L3 (we were aiming for 90mm past that lens but deemed this to be close enough). This was evaluated by measuring the beam size with the BeamScan at two different locations along the optical axis and projecting out where the focal point would be.
3. Next we aligned the beam through the output system making sure it was centered on all the mirrors.
4. Lastly, we adjusted the final mirrors so the beam went through the center of the iris that was mounted on the telescope.
5. We turned on the HWS (sans Hartmann plate) and saw a clipped return beam on it. We adjusted the output mirror to improve the return beam and remove the clipping. We used the sharp edges of the beam as a guide to center the intensity on the optic.
6. The 60mm focal length lens return beam is shown below. We deemed this to be the best return beam yet.
Old SLED beam for reference
The old ETMY HWS beam with the LED is shown here for reference.
Imaging the ETM
We moved the HWS along the optical axis, pitched ETMY up by a 20 microradians and measured the displacement on the CCD of the top edge of the HWS return beam.
Magnification
Average of 4 measurements = 22.8x
Method 1: (use the shadow of the SSTL BAFFLE PLATE)
- aperture size on HWS = 677 pixels = 8.11mm
- aperture size on D1102297 = 7.48" = 190mm
- M = 190/8.11 = 23.4x
Method 2: (nominal distances between optics)
| Parameter | Value |
| ETM to TMS primary [T1000717] | 1.429m |
| TMS primary ROC | 4.0m |
| Primary to Second | 1.9026m |
| TMS secondary ROC | -0.2m |
| Secondary to lower periscope mirror [T1000717] | 3.744m |
| LPM to Lens 1 [aLOG 52500] | 0.591m |
| Lens 1 FL [T1000717] | 2.2361m |
| Lens 1 to Lens 2 [aLOG 52500] | 0.610m |
| Lens 2 focal length [T1000717] | 2.2361m |
| Lens 2 to Lens 3 | 1.096m |
| Lens 3 to M6 [aLOG 52500] | 0.326m |
| M6 to HWS (measured today) | 0.472m |
ABCD Matrix:
The nominal ABCD matrix suggests that we're offset from the image plane by 18mm. The magnification is 1/0.0450146 = 22.2x
Method 3: Ratio of OPLEV PIT/YAW to HWS PIT/YAW when injection is added.
We added PIT and YAW excitations at different times into the ETMY SUS. We plotted the resulting HWS and OP LEV measurements of PITCH and YAW. The HWS measurements have been divided by the nominal magnification (H1:TCS-ETMY_HWS_MAGNIFICATION = 20.5) to reference them back to the plane of the HWS and divided by another factor of 2 to account for the fact that the OP LEV measures AOI and the HWS measures 2x AOI.
We fit for the linear sections in the attached plots. Depending on the ranges, the slopes ranged between 21.1 and 24.5, with an average of 22.8
