SOW_Document Number SLAC-I-120-104-R0.pdf

NC/SC Linac Statement of Work

Document Title: THz Transport Optics, Mounts, and Actuators

Document Number: SLAC-I-120-104-R0 Page 1 of 8

The only official copy of this file is located in the Controlled Document Management System.

Before using a printed/electronic copy, verify that it is the most current version.

Document Approval: Date Approved

Originator: Meredith Henstridge; Research Associate

Approver: Zhirong Huang; Project Manager

Approver: Alan Fisher; Project Physicist

Approver: Matthias Hoffmann; Project Physicist

Reviewer: Gen e Kraft; Project Engineer

Reviewer: Michael Kosovsky; Project Engineer

Revision History

Revision Date Released Description of Change

R0 5/3/2022 Original Release.

Table of Contents

1 Introduction

2 Purpose

3 Scope

3.1 General

3.2 Index of Required Products

4 Kick-Off Meeting

5 Written Status Reports

6 Noncompliance Issues

7 Specifications

7.1 Custom Off-Axis Parabolic Mirror #1

7.2 Custom Off-Axis Parabolic Mirror #2

7.3 Custom Planar Mirrors

7.4 3 Inch Kinematic Mirror Mounts

7.5 2 Inch Kinematic Mirror Mounts

7.6 Actuators for 3” Mounts

7.7 Drivers for Combined Manual-Piezoelectric Actuators

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1 Introduction

SLAC National Laboratory has proposed the building of a THz-based wiggler to be used with LCLS- II. The wiggler would produce pulses in the range of 3 THz - 30 THz with energies on the order of tens of microjoules. This would allow for new experiments at LCLS-II in which THz pulses are used to excite highly non-equilibrium conditions in complex materials while the ultrafast structural dynamics are monitored using x-ray probing methods. Successful implementation of this wiggler-based THz source involves the transport of THz radiation from the undulator hall over a distance of 100 - 300 meters to user stations located in the near and far experimental halls.

Currently, SLAC is carrying out preliminary studies in order to determine the best method for transporting THz radiation from the prospective wiggler over these large distances. A prototype reduced-scale vacuum transport system which carries out “relay-imaging” of THz radiation over a distance of 25 meters using both planar mirrors and off-axis parabolic mirrors has been designed and reviewed, and the components are in the process of being procured. The aforementioned optical mirrors require specifications which are not found in standard catalogs; hence custom solutions must be pursued.

2 Purpose

SLAC National Lab requires custom off-axis parabolic mirrors, planar mirrors, kinematic mounts, and actuators that fit within the vacuum chambers of the transport system. The supplier must provide products which fit all specifications as outlined in this document. Products which require vacuum compatibility must meet the LCLS Specification and Guidelines for Level 4 Vacuum Qualification (Document Number SLAC-I-030-714-001-07).

3 Scope

3.1 General

The supplier must design, manufacture, and test the products so that they meet all specifications provided in this document. The supplier is responsible for the secure packaging and the safe delivery of the products to SLAC. As part of the delivery process, the supplier must provide documentation indicating that the custom products meet the specifications listed in this document. Examples of such documentation include but are not limited to:

Measurements of the curvature of a finished parabolic mirror obtained via a coordinate measuring machine. These measurements would serve to indicate the theoretical effective focal length. Deviations from the ideal curvature must lie within the surface figure specified for a given mirror.

Schematics indicating the measured dimensions of a given product.

3.2 Index of Required Products

Item Quantity

Custom Off-Axis Parabolic Mirror #1 4

Custom Off-Axis Parabolic Mirror #2 2

Custom Planar Mirrors 4

3-Inch Kinematic Mirror Mounts 8 (possibly plus 2, see sec. 7.4 – 7.5)

2-Inch Kinematic Mirror Mounts 2 (possibly minus 2, see sec. 7.4 – 7.5)

Actuators (either combined manual-piezoelectric or fully motorized)

Actuators, mechanical (see section 7.5) 6

Driver for Combined Manual-Piezoelectric Actuators See section 7.7

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4 Kick-Off Meeting

Within 10 business days of contract execution, the supplier must hold a kick-off meeting with the buyer and relevant representatives in order to confirm an understanding of all design parameters outlined in this document. It should be emphasized that the Kick-Off Meeting serves primarily to confirm a mutual understanding between the buyer and the vendor concerning the design parameters. The vendor must determine whether their capabilities are suitable for producing the products described in this document and pose all relevant questions and concerns to the buyer before the execution of the contract.

5 Written Status Reports

Within 5 business days of the Kick-Off Meeting defined in Section 4, the vendor must provide a timeline for the primary steps involved in the manufacturing of the custom products. Additionally, the vendor must provide written status reports as mutually agreed upon during the Kick-Off Meeting defined in Section 4. The vendor must notify the buyer of any projected changes to the provided timeline as well as any other incidents that would postpone the delivery date of the products.

6 Noncompliance Issues

The vendor must notify the buyer of any problems that arise. This includes but is not limited to:

Problems which may prevent the vendor from manufacturing the purchased components to the specifications outlined in this document.

Problems which lead to the postponing of the delivery date.

Non-compliance of any nature shall be reported within one week to the buyer. Resolution shall be agreed upon by the buyer and the vendor and documented by the buyer’s procurement official.

7 Specifications

7.1 Custom Off-Axis Parabolic Mirror #1

Quantity: 4

The off-axis angle must be 90 degrees.

The mirror begins as an elliptical planar mirror blank that is then diamond turned to have the figure of the required OAP, as illustrated in the figure below. This reduces the cantilevered weight and the overall size, which is necessary to fit the mirror into the vacuum chamber discussed later and shown in Figure 2.

The length of the minor axis of the elliptical surface must be between 100 mm and 101.6 mm (4 inches).

The length of the major axis of the elliptical surface must be between 141.4 and 143.7 mm.

The clear aperture must be at least 95% of the ellipse spanned by the major and minor axes given above.

The effective focal length must be 3000 mm ± 1%.

The surface figure must be no greater than 1 wavelength (RMS) at 633 nm over the entire clear aperture.

The surface roughness must be less than 20 nm RMS.

The substrate must be aluminum (6061).

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The coating on this substrate must be bare (unprotected) gold. However, if the vendor can offer a form of protected gold that exhibits a reflectivity exceeding 97% at frequencies near 3 THz and 30 THz and would not distort picosecond THz pulses, then we would consider this option.

The buyer must approve the coating proposed by the vendor before the vendor proceeds with fabrication.

We require a custom machining process. We ask that the vendor fabricate the mirror from an elliptical blank and employ diamond turning on the front surface to obtain the appropriate curvature. The mirror must fit into a high stability 3-inch kinematic mount described in section

7.4.

Figure 1 illustrates one approach. Material is removed from the back surface of a blank of at least 40 mm thickness to form a circular boss with a 3” diameter and thickness of at least 20

mm. This boss must be held securely in the 3” kinematic mount described in section 7.4. The ellipse supporting the front surface should have a thickness between 20 and 25 mm.

We will consider an alternative mounting proposal that does not stress the mirror's front surface or that recreates the stress involved in diamond turning. The mounting proposal must be described in the vendor’s bid and approved by the buyer.

After machining and coating, the mirror must be cleaned for use in high vacuum (≤1 μTorr) and meet the LCLS Specification and Guidelines for Level 4 Vacuum Qualification (See section 2).

Figure 1: An OPA machined from an elliptical blank via the custom process described in section 7.1. Side view (above), rear view (below).

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7.2 Custom Off-Axis Parabolic Mirror #2

Quantity: 2

The off-axis angle must be 90 degrees.

The length of the minor axis of the elliptical surface must be between 75 mm and 76.2 mm (3 inches).

The length of the major axis of the elliptical surface must be between 106.1 and 107.8 mm.

The clear aperture must be at least 95% of the ellipse spanned by the major and minor axes given above.

The effective focal length must be 1000 mm ± 1%.

The surface figure must be no greater than ¾ wavelengths (RMS) at 633 nm over the entire clear aperture.

The surface roughness must be less than 20 nm RMS.

The substrate must be aluminum (6061-T6).

The coating on this substrate must be bare (unprotected) gold. However, if the vendor can offer a form of protected gold that exhibits a reflectivity exceeding 97% at frequencies near 3 and 30

THz and would not distort picosecond THz pulses, then we would consider this option. The coating must be described in the vendor’s bid and approved by the buyer.

The mirrors may be fabricated using a custom process similar to the one described in section

7.1, except that the thickness of the final elliptical surface should range from 15 – 20 mm, and the circular boss should be 2” in diameter. The final tolerances for the diameter and thickness of the circular boss should be such that the boss can be mounted securely into the 2” kinematic mount described in section 7.5.

Alternatively, since these mirrors will be outside the vacuum, they may be made as conventional wedge-shaped OAPs, in the form of a cylinder with a diameter of 75 mm (or 3 inches) with one end cut at 45 degrees and diamond turned to the OAP figure. They must otherwise conform to all other specifications. The choice of fabrication process must be described in the vendor’s bid and approved by the buyer.

7.3 Custom Planar Mirrors

Quantity: 4

The surface of each mirror must be elliptical.

The length of the minor axis of the elliptical surface must be between 75 mm and 76.2 mm (3 inches).

The length of the major axis of the elliptical surface must be between 106.1 and 107.8 mm.

The clear aperture must be at least 95%

The coating on this substrate should be bare (unprotected) gold. However, if the vendor can offer a form of protected gold that exhibits a reflectivity exceeding 97% at frequencies near 3 and 30 THz and would not distort picosecond THz pulses, then we would consider this option.

The coating must be described in the vendor’s bid and approved by the buyer.

The substrate material should be aluminum (6061-T6).

The surface figure must be no greater than ½ wavelength (RMS) at 633 nm over the entire clear aperture.

The surface roughness must be less than 20 nm RMS.

The mirrors must be fabricated using the custom machining and mounting options described in section 7.1.

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After machining and coating, the mirror must be cleaned for use in high vacuum (≤ 1 μTorr) and meet the LCLS Specification and Guidelines for Level 4 Vacuum Qualification (See section 2).

7.4 3 Inch Kinematic Mirror Mounts

Quantity: 8

The mounts must be machined from heat-treated stainless steel.

The mounts must have 3 degrees of freedom (tip-tilt-translate).

The angular range for tip and tilt must be at least ±2°.

The mounts must be able to securely hold the 3” circular boss on the back of the elliptical mirrors described in sections 7.1 and 7.3 with minimal distortion to the front surface. (As noted in 7.1, we will consider alternative mounting concepts.)

The mounts must support the actuators described in section 7.6.

The mounts must be compatible with high vacuum (≤1 μTorr) and meet the LCLS Specification and Guidelines for Level 4 Vacuum Qualification (See section 2). Any lubricant used must meet

Low Outgassing Standards NASA ASTM E595 for vacuum levels ≤1 μTorr

The combined mirror/mount/actuator assembly must fit inside the vacuum chamber shown in

Figure 2.

These mounts must exhibit a low level of hysteresis with respect to temperature changes. Upon cycling the ambient temperature by 5°C, the pointing of a mirror held by the mount must return to its original position within 10 µrad.

Figure 2: Schematics of the vacuum chamber housing each large mirror assembly (mirror + mount + actuator), including both the four #1 custom OAPs and the four custom plane mirrors. Left: top-down view, Right: side-view. The mirror will be positioned such that the angle of incidence with respect to both vacuum ports is 45 degrees. The assembly will be aligned so that the center of the mirror’s front surface corresponds to the center of the vacuum chamber. The final dimensions of the mirror assembly must fit within the 197.1-mm inner diameter of the vacuum chamber.

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7.5 2 Inch Kinematic Mirror Mounts

Quantity: 2

The mounts should be machined from heat-treated stainless steel.

The mount must be able to securely hold a 2” circular boss on the back of an elliptical mirror described in section 7.2 with minimal distortion to the front surface. (As noted in 7.1, we will consider alternative mounting concepts.)

However, if the #2 OAPs of section 7.2 are made in the conventional wedge style, we will accept a 3-inch mount that otherwise conforms to these specifications. The mount must be adapted to securely hold the off-center weight of a wedge OAP using more than the usual set screw on one side of the rim. We suggest a plate that secures the OAP to the mount using tapped holes in the rear of the OAP. See Figure 3 for a sketch illustrating this concept for securing the mirror. The mounting solution must be presented in the vendor’s bid and approved by the buyer.

The mount must have 3 degrees of freedom (tip-tilt-translate).

The angular range for tip and tilt must be at least ±2°.

The mounts must be supplied with compatible mechanical actuators that have a resolution of at least 100 threads per inch.

The mounts must exhibit low levels of hysteresis with respect to temperature changes. Upon cycling the ambient temperature by 5°C, the pointing of a mirror held by the mount should return to its original position within 10 µrad.

Figure 3: Schematics of a mounting scheme for a wedge-style off-axis parabolic mirror.

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7.6 Actuators for 3” Mounts

Quantity: 24

The actuators must be compatible with the vendor’s solution for the 3” mirror mounts described in Section 7.4.

The actuators must have a range of travel compatible with the angular tip-tilt range specified for the mounts.

The actuators must be capable of remote actuation, at least over a portion of their range. This could involve a combination of manual and piezoelectric adjustment capabilities, or fully motorized motion.

The position of each actuator must be recoverable in the case of a sudden power cut to the system or for restoring a previous alignment. Note that we can record the voltage on a piezo stack, the step count of a stepper motor, or the reading of an encoder. This information can be used to restore the position, perhaps after homing the actuator. Other drive mechanisms, such as piezo screw-turners, do not have repeatable step and so must be accompanied by a readback device.

The actuators must be compatible with high vacuum (≤1 μTorr) and meet the LCLS

Specification and Guidelines for Level 4 Vacuum Qualification (See section 2). Any lubricant used must meet Low Outgassing Standards NASA ASTM E595 for vacuum levels ≤1 μTorr.

When three actuators are inserted into a mirror mount, the assembly must be sufficiently compact to fit inside the vacuum chamber, given the chamber dimensions and mounting constraints described in section 7.4 and illustrated in Figure 2.

7.7 Drivers for Combined Manual-Piezoelectric Actuators

The driver must be compatible with the vendor’s solution for the actuators described in section

7.6.

If the vendor proposes combined manual-piezoelectric actuators, we will need a 24-channel driver, or several multi-channel drivers totaling 24 channels.

We already have satisfactory drivers (three 8-channel Newport XPS controllers) for 24 stepper or DC motors.

The driver must provide a reading for each channel to record the exact positions of the actuators, for recovery after a power outage or restoring a previous alignment.