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Enhancing Applicability of Volume Phase Holographic Gratings in Astronomy

JRA-6 aims to optimize volume phase holographic gratings (VPHGs) for astronomical instrumentation. The project focuses on improving efficiency, exploring new configurations, and developing VPHGs for cryogenic and UV applications.

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Enhancing Applicability of Volume Phase Holographic Gratings in Astronomy

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  1. JRA-6 Mid-Term Report Filippo Maria Zerbi on behalf of JRA-6 Team

  2. JRA 6 in a Nutshell JRA-6 is entitled “Volume Phase Holographic Gratings” • The following Contractors contribute to JRA-6: • ESO European Southern Observatory (INT) • IAC Instituto de Astrofisica de Canarias (E) • INAF Istituto Nazionale di Astrofisica (I) • Osservatorio Astronomico di Brera (Coordinator) • Politecnico di Milano (I) • Diapartimento di Ingegneria Chimica • Universitè de Liege (B) • CSL Centre Spatial de Liege (ATHOL) Purpose of the JRA-6 is to enhance the applicability of VPHGs in Astronomical Instrumentation

  3. VPHGs ?

  4. VPHGs ? a “slice” of photosensitive material with n modulated by an interferometric pattern of fringes grooved in by holography. The PS-material is embedded in glass components, active or passive following the optical design, that can be AR-coated The orientation of the fringes determines the reflection or transmission behavior.

  5. VPHGs ? Regular pattern of varying refractive media with scale-length of the same order as . Multiple reflection and diffraction in a multi-layer configuration

  6. VPHGs ? • VPHGs Efficiency Predicted via RCW-Theory - Commercial or custom • codes (U-Mich – INAF-Brera). • “Back of an envelope” estimates via the Kogelnick (1962) approximation Crucial Quantities There is a pair B, 2B for which maximum coherence/efficiency is reached For a given *2B minimum coherence/efficiency is reached for = B ± . This defines the BLAZE function B(, *2B) If we scan the Bragg angle (e.g. rotating the VPHG) the maximum coherence/efficiency is reached at different  values. This defines the SUPERBLAZE function SB(B, 2B).

  7. VPHGs ? Blaze and superblaze are at some extent “tunable” in width and height to ones needs fiddling with n and L

  8. VPHGs ? Photosensitive Material ? Baseline: Dichromated Gelatin • PROs • Very High Transmission in VIS-NIR • Suited for (n L) needed for gratings • CONs • Dirty Wet Chem Post-processing • Higroscopic • No redder than K-band THE limit to VPHGs performances

  9. Relevanceof VPHGs in Astronomy

  10. VPHGs in Astronomy Gain Efficiency

  11. OPTICON- JRA6 VPHGs in Astronomy Easy Handling and Maintenance

  12. VPHGs in Astronomy • As Grism in low resolution spec. • Implemented: • AFOSC@ ASIAGO 1.8 mt • d.o.lo.re.s @ TNG 3.6 mt • FORS@VLT 8.2 mt • VIMOS@VLT 8.2 mt • Planned: • EFOSC@ESO 3.6 mt • EMIR@GTC 10mt • MUSE@VLT 8.2 mt • XXX@EELT 42mt • As Cross Disperser in HR spec. • Planned: • UVES@VLT 8.2 mt • Espresso@VLT 8.2 mt • CODEX@EELT 42mt • As Core element in HR spec. • Planned: • SONG Project (0.8 mt) • REM Telescope (0.6 mt) • ………..

  13. Status “ANTE-OPTICON”

  14. Status “ANTE” • First fully functional prototype used at AAO (K.Taylor, G.Robertson) – 1997(8) • Pioneering USA work under NSF grant at NOAO (Sam Barden) collaboration with Kaiser Optical (Jim Arns) -1997-2000 (single world producer at the time). • Richard Rallison (Utah) steps into the market with cheap (but not always • science-grade) devices – 1999 • Chris Clemens hosts at UNC two “thinkshops” (1999 and 2000) • to join efforts of the astronomical community toward the use of VPHGs

  15. Status “ANTE” • Dimensions. First problem to solve. • Kaiser Optical and Rallison max size 10 cm. • Pupils of exisiting instruments 20 cm. ELTs pupils >40 cm • Players. Second problem to solve. • As single HQ player on the market implies vendor dictates the rules • Astronomy needs “outsourcer reactive to stimuli”, i.e. competition • USA. Third “problem” to solve. • The EU-USA competition (or “coopetition”) in Astronomy is high. • USA technology is “not always” available to other countries

  16. Co-leaders Status “ANTE” Financial Contribution in “stocks” of 12.5 k€ entitling to receive 1 VPHG at wish Goal:Creation of a pole (spin-off) to produce large size Astronomical VPGHs in Europe

  17. Status “ANTE” ATHOL Partner of JRA-6 through ULG

  18. JRA-6 Goals and Timeline

  19. JRA-6 Goals • Selected Areas of research • IR VPHGs: Enable VPHGs technology in the NIR (1-2.5 microns) regime in cryogenic instruments. • UV VPHGs: Enable VPHGs technology in the UV (300-450 nm) regime with particular attention to cross dispersers. • DCG Replacement: Look for a replacement of the DCG as photosensitive element. • Non-traditional Configurations: Enhance the applicability of “traditional” VPHGs.

  20. JRA-6 Goals • JRA-6 programme (OPTICON Contract Annex 1) is aimed to: • WP2 - Fabrication of fully functional VPHGs working at cryogenic (77 k) temperature and optimized for IR (1-2.5 µm) wavelengths • WP3 - Improved perfromances VPHGs at visible wavelengths with • attention to cross-dispersion, tuneability of the resolution, FPA filling. • WP4 - Fabrication of the first laboratory-level re-writeable VPHG based on photochromic polymers. • Added at Kick-off (as re-destribution of WP workload): • WP5 – Fabrication of fully functional VPHGs working at UV (300-450 nm) wavelengths with special care to cross-dispersion.

  21. JRA-6 Goals • JRA-6 general (for each WP) milestones scheme: • Definition of a prototype characteristics • Fabrication of the prototoype • Analysis and characterization of the prototype • Definition of the final deliverable characteristics • Production of the final deliverable • Analysis and characterization of the final deliverable • Final product dossier editing. • JRA-6 detailed milestones scheme (Annex I of OPTICON Contract) • 6 milestones (M1-M6) specializing the above scheme to each WP

  22. JRA-6 Goals Prototyping Phase Final deliverable Phase

  23. WP-2 IR VPHGs

  24. WP-2 Prototype Definition

  25. WP-2 Prototype Manufacturing

  26. WP-2 Specific Setup built

  27. WP-2 Efficiency

  28. WP-2 Higher Order Contamination

  29. WP-2

  30. WP-2 small grating: 95% efficient at 633 nm, Bragg 25°.

  31. WP-2 Ongoing Activity • Full Cryo-analysis of specific IR prototypes (delayed). • Definition of Science Grade devices characteristics. • Procurement of the substrates for the Science Grade devices. Planned Activity • Manufacturing of the Science Grade Devices • Characterization of the Science Grade Devices

  32. WP3 Non Traditional Configurations

  33. WP-3 A) VPHG-based Tunable narow-band FIlter B) Multiple trace VPHG HR spectrograph

  34. WP-3 Tunable Filters

  35. WP-3 HR Spec.

  36. WP-3 & WP-5 Double Pass UV Cross Disperser

  37. WP-3 Ongoing Activity • Construction of the Mechanical parts of HR spec. (delayed) • Definition of specific VPHGs for the Tunable Filter • Procurement of the substrates for the VPHGs Planned Activity • Integrating and Testing the HR spectrograph. • Integrating and Testing the Tunable Filter .

  38. WP-4 Photochromic Polymers

  39. WP-4 Write with light - Wipe with Light - Re-write with light Non linear – Polarizability (n) Linear - Transparency

  40. WP-4 Zoology derived for OTPICON applications “LEGO Chemistry”

  41. WP-4

  42. WP-4 Ongoing Activity • Production of Better Quality Photochromic Films • Definition of the Final deliverable Characteristics Planned Activity • Production of a Higher Performances Phot-VPHGs • Characterisation of its perfromances.

  43. WP-5 UV VPHGs

  44. WP-5 Prototype Definition

  45. WP-5

  46. WP-5 Efficiency

  47. WP-5 Transmitted Wavefront

  48. WP-3 & WP-5 Double Pass UV Cross Disperser

  49. WP-5 Efficiency New set of prototypes manufactured

  50. WP-5 Ongoing Activity • Characterization of the new set of prototypes (delayed) • Definition of Science Grade devices characteristics. • Procurement of the substrates for the Science Grade devices. • Procurement of the prism for Cross-disperser-configuration Planned Activity • Manufacturing of the Science Grade Devices • Characterization of the Science Grade Devices

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