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

2. iBTF module (as built) VPHG 1 VPHG 2 with 40mm D-Gs 2-by-2 mosaic z-stage

3. iBTF – 3 axes motors (as built) VPHG 1 Rotation only VPHG 1 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°): 1. The grating rulings of the VPHGs are required to be parallel; ~1’ or ~30  m at edge 2.The surfaces of the VHG gratings (VPHGs) are required to be parallel; R X ~3” ; T X ~1’ – constrained not by counter-dispersion requirement but to avoid image motion with scan Furthermore, in order to scan the iBTF in wavelength: 3.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 iBTF P : 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. iBTF P 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 (VPHG 1 & 2 ) should be coincident with X-axes of M1&M2 Grating rulings of VPHG 1 & 2 should be parallel – Requires rotation @ y-axis … to what tolerance?

11. Alignment Procedure Mounting of iBTF P 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 – iBTF P = iBTF module in BTFI