Brazilian Tunable Filter Imager (BTFI) Preliminary Design Review (PDR) ‏

1. Brazilian Tunable Filter Imager(BTFI)Preliminary Design Review (PDR)‏ iBTF module Prototyping Version 1.0 USP-IAG Universidade de São Paulo 18-19th June 2008

2. iBTF module (as built) z-stage VPHG1 • VPHG2 with • 40mm D-Gs • 2-by-2 mosaic

3. iBTF – 3 axes motors (as built) • VPHG1 • Rotation only • VPHG1 • Rotation • Translation

4. iBTF Grating mount(as built) D-G 2-by-2 mosaic (Ondax) on substrate Grating holder (individual) Grating mount (adjustable in roll)

5. It works!Thanks to Rene, Reitano (INPE); Giseli, Fernando (USP);Cesar & Ligia de Oliveira (LNA)

6. Close up view

7. Control electronics bird’s nest

8. Fundamentals • In order to effect dispersion cancellation at all angles of the VPH grating (VPHG) pair (between 25° and 45°): • The grating rulings of the VPHGs are required to be parallel; • ~1’ or ~30m at edge • The surfaces of the VHG gratings (VPHGs) are required to be parallel; • RX ~3” ; TX ~1’ – constrained not by counter-dispersion requirement but to avoid image motion with scan • Furthermore, in order to scan the iBTF in wavelength: • The image transmitted by the VPHG pair should remain stationary during the wavelength scan; • 1-pixel ~10” – but more relaxed with flexure monitoring

9. Coordination • Motor identification: • M1 – Fixed rotation stage • M2 – Moving rotation stage • M3 – Linear translation stage on which M2 is moved • Fundamental axes of the iBTFP: • Z-axis: defined by the linear translation stage on which M2 is mounted • X-axis: defined by the rotation axis of M1 • Y-axis: experimentally defined by the gravitational vector in the plane of rotation of M1

10. iBTFP geometry • Input optical axis (O-axis) • Translation stage (Z-axis – M3) • O&Z-axes should be coincident • Rotation axis of M1 (X-axis) • X-axis & O/Z-axis should be orthorgonal • Rotation axis of M2 should be parallel to M1 • Y-axis defined by gravity vector (arbitrary) • Grating surfaces (VPHG1&2) should be coincident with X-axes of M1&M2 • Grating rulings of VPHG1&2 should be parallel • Requires rotation @ y-axis … to what tolerance?

11. Alignment Procedure • Mounting of iBTFP and laser on optical bench • Laser directed along z-axis; y-axis defined by gravity vector • Zero-point and rotation direction of M1 and M2 • Defined using software control of M1 and M2 • Establishing Y-axis alignment with the gravitational vector • Accurate spirit level • Establishing parallelism between rotation axes of M1 and M2 • Rotation @ y-axis unavailable; require shims on motor mount • Establishing laser alignment with the Z-axis • Use pin-hole and z-translation stage (M3) • Establishing orthogonality of M2 mirror surface with Z-axis • No rotation @ y-axis – used mirror on 2D mount • Establishing orthogonality of M1 mirror surface with Z-axis • Again no y-axis adjustment on M1 • Establishing orthogonality of the Z-axis with the X-Y plane • Uncritical (tbd)

12. Still to be done • Final alignment using: • Laser, 2D-adjustable mirrors, shims and spirit-level • Install VPHGs • from Ondax (Rx ; doped-glass) • Check dispersion cancellation • Check stationarity of image during scan

13. Preliminary conclusions • Basic z-configuration design works? • Electro-mechanically – Yes • Optically • Reflection tests – Yes • Dispersion tests – Probably (tbc) • What needs to be changed? • Y-axis adjustment of M2 • Shims will be adequate • Y-axis adjustment of grating mount • Design modification in hand • Fundamental conclusion • iBTFP = iBTF module in BTFI