Ian Powell

Lenses for correcting chromatic aberration of the eye.

Optical systems for correcting the axial chromatic aberration of the eye are studied theoretically. Compact (cemented) doublets or triplets for this cannot avoid introducing unwanted transverse color. A new airspaced system is described which avoids this problem. Experimental results confirmed that this lens performed well over a 14-deg field of view.

Wavelength-dispersive device based on a Fourier-transform Michelson-type arrayed waveguide grating

We propose a new type of arrayed waveguide grating (AWG) device that operates as a Fourier-transform (FT) spectrometer without the need of scanning elements. The large input aperture size typical of a FT spectrometer eliminates the requirement for a narrow single-mode input waveguide while still achieving high spectral resolution with a markedly increased light-gathering capability (etendue). An example of the device with a resolution of 0.07 nm (approximately 10 GHz) and designed for a silicon-on-insulator platform is presented. The calculated spectra show no noticeable deterioration for aperture widths as large as 40 microm, yielding more than a 50-fold increase in aperture size compared with conventional AWG or echelle grating based devices at the equivalent resolution.

Design of a laser beam line expander

The design of an optical element for laser beam line expansion is described. The element which bears some resemblance to a prism with a small radius at its apex expands the laser beam in one direction only. The technique for designing such a lens is given together with examples of lenses having different rates of divergence.

ABSOLUTE FIGURE MEASUREMENTS WITH A LIQUID-FLAT REFERENCE

We describe a variation of the liquid-flat technique fordetermining the absolute flatness of a 240-mm-diameter optical surfaceto an accuracy better than 1/100lambda in both its horizontal(three-point support) and vertical orientations. Using theappropriate mathematics to calculate the surface deformation of a diskdue to gravity, we achieved verification of the method by comparingmeasurements carried out on a pair of optical flats and a liquidreference surface.

A conceptual design for the Thirty Meter Telescope adaptive optics systems

In this paper, we provide an overview of the adaptive optics (AO) program for the Thirty Meter Telescope (TMT) project, including an update on requirements; the philosophical approach to developing an overall AO system architecture; the recently completed conceptual designs for facility and instrument AO systems; anticipated first light capabilities and upgrade options; and the hardware, software, and controls interfaces with the remainder of the observatory. Supporting work in AO component development, lab and field tests, and simulation and analysis is also discussed. Further detail on all of these subjects may be found in additional papers in this conference.

Design study of an infrared panoramic optical system

A design study was undertaken on an infrared, 3-5-μm, panoramic optical system for a particular monitoring application. The different types of systems investigated covered the conventional fish-eye lens system, a panoramic block arrangement, and a new type of configuration based on a panoramic shell. Examples of these systems are included, and their advantages and disadvantages are discussed.

Development of optical monitor for control of thin-film deposition

The design of a multichannel optical monitor for transmittance measurements of thin-film coatings during deposition is described. The system comprises a light source and one or more spectrum analyzers each incorporating a prism monochromator and a 256-element photodiode array detector. This multiple-channel design, in conjunction with an HP 1000 computer and data acquisition period of 100 ms, enables the coating uniformity to be precisely monitored and controlled. High-system throughput has been achieved with a large numerical aperture (f/1.5), while retaining excellent spectral resolution over the 350–1100-nm wavelength range. Experimental measurements indicate a practical resolution equal to the detector-limited resolution, a wavelength reproducibility of 0.1 nm at 400 nm and 0.6 nm at 700 nm, and a photometric accuracy and precision of ~1 and ±0.3%, respectively. The problem of unequal energy distribution across the spectrum is handled by optical rather than the usual electronic compensation.

Modeling of the generic spatial heterodyne spectrometer and comparison with conventional spectrometer

We describe the modeling of the generic spatial heterodyne spectrometer. This instrument resembles a somewhat modified Michelson interferometer, in which the power spectrum of the input source is determined by performing a one-dimensional Fourier transform on the output intensity profile. Code has been developed to analyze the performance of this type of spectrometer by determining the dependence of both spectral resolution and throughput on parameters such as aperture and field of view. An example of a heterodyne spectrometer is developed to illustrate the techniques employed in the modeling and a comparison undertaken between its performance and that of a conventional spectrometer. Unlike the traditional Fourier transform infrared system, the heterodyne spectrometer has the very desirable feature of having no moving components.

Employment of reverse optimization to relax manufacturing tolerances imposed on system constructional parameters associated with complex optical systems

I describe a practical method for facilitating the construction of a complex optical arrangement that was extremely sensitive to manufacturing defects. I discuss dealing with the actual tolerancing process employed and outline the reverse optimization technique adopted to take the necessary corrective action with regard to the lens to yield the performance specified. The optical design to which the techniques are addressed is that of a high-performance color-corrected scanner lens, capable of resolving 200 line pairs/mm over a 10-mm(2) object.

Short-wave infrared (SWIR) imaging spectrometer for remote sensing

The SWIR full spectrum imager (SFSI) is an imaging spectrometer, covering the short-wave infrared (SWIR) from 1200 to 2400 nm, which has been developed for remote sensing from an airborne platform. The sensor has been designed to acquire the full spectrum at high spectral resolution (10 nm) and the full image swath at high spatial resolution (50 cm) simultaneously. The instrument utilizes a platinum silicide (PtSi) detector array, refractive optics, and a transmission grating. A VME bus computer communicates with the array controller, performs the data acquisition, and provides the operator interface. The camera and data acquisition subsystems have been completed and test flown. The fore-optics, spectrograph, and sensor housing have been fabricated. Integration of the camera, spectrograph, and auxiliary components is scheduled for July 1994 followed by laboratory testing and calibration. Our goal is to obtain pilot project data by the end of autumn 1994. Here we describe the optical design, the sensor system, early test flight image data, and expected sensor performance based on laboratory testing. The objectives and procedures for the spectral, geometric, and radiometric calibration of this sensor are also discussed.