Brazilian Tunable Filter ImagerBrazilian Tunable Filter Imager(BTFI)(BTFI)

Preliminary Design Review (PDR)Preliminary Design Review (PDR)

USP-IAG Universidade de São PauloUSP-IAG Universidade de São Paulo

18-19th June 200818-19th June 2008

iBTF module PrototypingiBTF module PrototypingVersion 1.0Version 1.0

iBTF module(as built)

VPHG1

VPHG2 with• 40mm D-Gs• 2-by-2 mosaic

z-stage

iBTF – 3 axes motors(as built)

VPHG1

• Rotation only

VPHG1

• Rotation• Translation

iBTF Grating mount(as built)

D-G 2-by-2 mosaic (Ondax) on substrate

Grating holder (individual)

Grating mount(adjustable in roll)

It works!Thanks to Rene, Reitano (INPE); Giseli, Fernando (USP);

Cesar & Ligia de Oliveira (LNA)

Close up view

Control electronics bird’s nest

FundamentalsIn 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 ~30m at edge

2. 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:

3. The image transmitted by the VPHG pair should remain stationary during the wavelength scan;• 1-pixel ~10” – but more relaxed with flexure monitoring

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

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?

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)

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

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