Lawrence Lesyna

Measurements of the phase shift on reflection for low-order infrared Fabry–Perot interferometer dielectric stack mirrors

A simple technique based on a Fizeau interferometer to measure the absolute phase shift on reflection for a Fabry-Perot interferometer dielectric stack mirror is described. Excellent agreement between the measured and predicted phase shift on reflection was found. Also described are the salient features of low-order Fabry-Perot interferometers and the demonstration of a near ideal low-order (1-10) Fabry-Perot interferometer through minimizing the phase dispersion on reflection of the dielectric stack. This near ideal performance of a low-order Fabry-Perot interferometer should enable several applications such as compact spectral imagers for solid and gas detection. The large free spectral range of such systems combined with an active control system will also allow simple interactive tuning of wavelength agile laser sources such as CO(2) lasers, external cavity diode lasers, and optical parametric oscillators.

A near IR Fabry-Perot interferometer for wide field, Low resolution hyperspectral imaging on the Next Generation Space Telescope

We discuss work in progress on a near-infrared tunable bandpass filter for the Goddard baseline wide field camera concept of the Next Generation Space Telescope Integrated Science Instrument Module. This filter, the Demonstration Unit for Low Order Cryogenic Etalon (DULCE), is designed to demonstrate a high efficiency scanning Fabry-Perot etalon operating in interference orders 1 - 4 at 30 K with a high stability DSP based servo control system. DULCE is currently the only available tunable filter for lower order cryogenic operation in the near infrared. In this application, scanning etalons will illuminate the focal plane arrays with a single order of interference to enable wide field lower resolution hyperspectral imaging over a wide range of redshifts. We discuss why tunable filters are an important instrument component in future space-based observatories.

Lockheed Martin team's Next Generation Space Telescope (NGST) reference architecture

An overview of the Lockheed Martin Teams NGST Reference Architecture is discussed. Our f/1 NGST concept includes a lightweight 8-meter primary mirror consisting of eight deployed petals. Alignment and figure control employs wavefront-sensing techniques. Infrared observations are enabled by using a tennis court size multi-layer deployed sunshield permitting the primary mirror to be passively cooled to < 40 K. Candidate Science Instruments cover the spectral range from 0.6 microns to greater than 20 microns. The Integrated Science Instrument Module (ISIM) is passively cooled to approximately 30 K. The Observatory is launched on an AtlasV-531M in 2008 and operates at the L2 LaGrange Point. Science Planning and Mission Operations are the responsibility of the Space Telescope Science Institute in Baltimore Maryland. The ISIM is the responsibility of Goddard Space Flight Center (GSFC). The Lockheed Martin Team, including Raytheon, Honeywell, and Jackson and Tull, is an NGST Phase 1 Prime Contractor. The GSFC manages the NGST Project in Greenbelt Maryland.

Development and testing of a MWIR Fabry-Perot interferometer for hyperspectral imaging

This paper describes the theory of design, operation, and testing of a tunable MWIR Fabry-Perot interferometer operating in low orders. This device is called the agile bandpass tunable filter (ABTF) due to the fact that the spectral bandwidth can be changed by a large factor by changing the order. In first order the system can be tuned over the entire 3.5-5 micrometers spectral region with only a single order sorting filter. We provide a short introduction to tunable filters an then briefly discuss the requirements that low order operation places on the Fabry-Perot dielectric mirrors. Operation in low orders forces one to abandon the classical Fabry-Perot approximation that the mirrors are negligibly thin compared to the plate separation. Rather, one must now account for the phase properties of the dielectric stack mirrors as they produce phase effects comparable to the plate separation. We next address the issue of control of the Fabry-Perot. This is accomplished through a closed-loop system using capacitive sensor on the Fabry-Perot flats to measure the separation of the plates. Additionally we describe how the ABTF is characterized using a FTIR to measure the bandpass shape and position, and we show some examples of measurements made with the ABTF used as a hyperspectral imaging system with a 256 X 256 HgCdTe camera. We conclude with a discussion of potential applications and future work.