New Methods for the Optical Design of Spectrometers with Freeform Surfaces

Transcription

1 New Methods for the Optical Design of Spectrometers with Freeform Surfaces Jacob Reimers, Kevin P. Thompson, Kevin L. Whiteaker, and Jannick P. Rolland Center for Freeform Optics (CeFO) The Institute of Optics, University of Rochester Ball Aerospace

2 FOV (mm) Y Field Outline Introduction Design tools for freeform surfaces 1 X Field Spectral full-field display X Field (mm) - Freeform spectrometer design example :3: Dyson Spectrometer Z/ 18-Jun-1. waves 13:1: Conclusion Position: 3 Offner-Chrisp F/3.8 Spectrometer Scale: MM 3-Apr-1

3 Introduction Designing pushbroom imaging spectrometers is challenging Slit field of view (FOV) 1:3: Dispersive element creates spectral FOV Often coupled with foreoptics Position: 3 Offner-Chrisp F/3.8 Spectrometer Scale: MM 3-Apr-1 Spectral FOV 3

4 Y Field Design tools for freeform systems The full-field display (FFD) has been successfully utilized in the design of a LWIR freeform imager In the context of spectrometer design, this requires a new, spectral, full-field display (SFFD) to be developed LWIR imager The SFFD will enable the aberration visualization and guide the design of freeform spectrometers K. Fuerschbach, J. Rolland, and K. Rolland-Thompson, "Realizing Freeform: A LWIR Imager in a Spherical Package," in Renewable Energy and the Environment, OSA Technical Digest (online) (Optical Society of America, 13), paper FW1B.. X Field Full-field display

5 Field of X Field view (mm) (mm) Spectral full-field display (SFFD) A new type of visualization for dispersive imaging systems that is: A plot of Fringe Zernike coefficients on field of view vs. wavelength Calculated on a term-by-term basis using real ray trace calculations Entrance slit 1 - Z ASTIG.λ Dyson Spectrometer Z/

6 Design example using freeform optics 1:3: Specifications: F/3.8-1 nm spectral bandwidth 1mm entrance slit length 1nm/mm dispersion 1:: Position: 3 Offner-Chrisp F/3.8 Spectrometer Scale: 1. YZ (dispersion) plane 1. MM 3-Apr-1 1mm Offner-Chrisp (OC) spectrometer Concentric Corrects spherical aberration 1-1 magnification Corrects coma and distortion Limited by astigmatism Ring field balance XZ (slit/field) plane Position: 1 Offner-Chrisp F/3.8 Spectrometer Scale: MM XZ 17-Jun-1 1mm M. Chrisp, "Convex diffraction grating imaging spectrometer," US Pat.,, (9).

7 OC spectrometer - All spherical performance 7 1::3 Z/ 17-Jun-1 MIN =.8E- MAX = 1. AVG =.37. waves All spherical surfaces: Max :.λ Avg. :.λ 1::1 18-Jun-1 MIN =.E- MAX =. AVG =.E-1. waves λ Z ASTIG.λ :3: Offner-Chrisp F/3.8 Spectrometer Scale: 1. Position: 3 3-Apr- 1. MM The maximum/average was calculated for all fields and wavelengths for comparison

8 Benchmarking with coaxial aspheres ZASTIG All surfaces aspheric (A-D): Max :.7λ Avg. :.λ λ All aspheric surfaces with astigmatic node shift: Jun-1. waves 1:9:3 Z/ - Max :.λ Avg. :.9λ MIN =.E- MAX = 1. AVG =.18 1:17:1 MIN =.E-1 MAX =. AVG =.9E-1 18-Jun-1. waves λ Z/ MIN =.E- MAX =. AVG =. 18-Jun-1. waves - Max :.18λ Avg. :.9λ 1::37 1::3 Anamorphic aspheric surfaces: MIN =.13E-1 MAX =.1 AVG =.E-1 18-Jun-1. waves Z/ MIN =.11E-1 MAX =.7 AVG =.9 8 MIN =.E-1 MAX =.

9 Benchmarking with coaxial aspheres ZASTIG All surfaces aspheric (A-D): Max :.7λ Avg. :.λ λ All aspheric surfaces with astigmatic node shift: Jun-1. waves 1:9:3 Z/ - Max :.λ Avg. :.9λ MIN =.E- MAX = 1. AVG =.18 1:17:1 MIN =.E-1 MAX =. AVG =.9E-1 18-Jun-1. waves λ Z/ MIN =.E- MAX =. AVG =. 18-Jun-1. waves - Max :.18λ Avg. :.9λ 1::37 1::3 Anamorphic aspheric surfaces: MIN =.13E-1 MAX =.1 AVG =.E-1 18-Jun-1. waves Z/ MIN =.11E-1 MAX =.7 AVG =.9 9 MIN =.E-1 MAX =.

10 Summary of benchmarking aspheres.λ Offner-Chrisp F/3.8 Spectrometer Position: 3 Scale: MIN =.E- MAX =. AVG =.E-1 MIN =.E-1 MAX =. AVG =.E-1 All spherical surfaces: 18-Jun-1. waves Max :.λ Avg. :.λ Anamorphic asphere: 1:1:7 1::1.λ 1:3: 18-Jun-1. waves Max :.18λ Avg. :.9λ Note: Avg. does not decrease appreciably 1 MM 3-Apr-

11 OC spectrometer - freeform performance 11 All freeform surfaces: Diffraction limited for all fields and wavelengths Max :.3λ Avg. :.1λ 1:3:3 Offner-Chrisp F/ Jun-1 MIN =.1E-1 MAX =.33E-1 AVG =.19E-1. waves :3:8 Offner-Chrisp F/3.8 Z/ 18-Jun-1 MIN =.3E- MAX =.1 AVG =.E-1. waves λ λ Z ASTIG 1:3: Offner-Chrisp F/3.8 Spectrometer Scale: 1. Position: 3 3-Apr- 1. MM Surfaces are of the φ- polynomial (Fringe Zernike) type Anamorphic asphere: Max :.18λ Avg. :.9λ All spherical surfaces: Max :.λ Avg. :.λ

12 . Freeform surface departures WAVEFRONT ABERRATION. New lens from CVMACRO:cvnewlens.seq Field = (.,.) Degrees Wavelength =. nm Defocusing =. mm Waves 1. Tertiary largest departure PV μm Exact shape may vary... Common to all surfaces: Dominated by Astigmatism < 1 μm departure Field = (.,.) Degrees Wavelength =. nm Defocusing =. mm. 1

13 Spherical vs. freeform OC spectrometer 1:3:.λ Offner-Chrisp F/3.8 Spectrometer Offner-Chrisp F/3.8 MIN =.E- MAX =. AVG =.E-1. waves 1:3:3 Spherical Avg. : 18-Jun-1 MM 3-Apr Position: 3 Scale: ::1.λ 18-Jun-1 MIN =.1E-1 MAX =.33E-1 AVG =.19E-1 Freeform. waves Spherical asphere % decrease Spherical anamorphic asphere % decrease Spherical freeform 8% decrease 13

14 Field of view (slit) Simultaneous achievement of optical performance and distortion correction Imaging spectrometers have two types of distortion Spectral smile Typically want to be <1% of a pixel Spatial keystone Typically want to be <% of a pixel Measured the deviation with respect to the centroid of each wavelength or field Distortion and imaging performance are a design trade-off for spectrometers consisting of all-spherical surfaces Freeform corrects smile/keystone while retaining diffraction limited performance in the Offner-Chrisp Wavelength Ideal Distorted Spectral broadened Offner-Chrisp was analyzed to have max.1μm smile and.8μm keystone which for a 1μm pixel is 1% and.8% respectively P. Mouroulis, R. O. Green, and T. G. Chrien, "Design of pushbroom imaging spectrometers for optimum recovery of spectroscopic and spatial information.," Appl. Opt. 39, 1 (). 1

15 Summary The SFFD calculates the magnitude and direction of Fringe Zernike coefficients and plots them on field of view vs. wavelength axes The SFFD assists the designer in the design of spectrometers Insights provided by nodal aberration theory and the SFFD motivate novel compact high performance freeform spectrometers The use of freeform surfaces in an Offner-Chrisp spectrometer enables a much wider spectral bandwidth than spherical or aspheric designs due to correction of the astigmatic field as seen using the SFFD Leveraging freeform in an Offner-Chrisp facilitates simultaneous optical performance and distortion correction 1

16 Acknowledgements NSF I/UCRC Center for Freeform Optics (CeFO) Ball Aerospace & Technologies Corp.; OptiPro Systems, LLC; PerkinElmer; PolymerPlus LLC; Rochester Precision Optics; SCHOTT North America, Inc.; Air Force Research Laboratory; Zygo Corporation; ARRI. Peter Marasco and Dennis Yates for the stimulating discussions Synopsys Inc. for the student license of CODE V 1