R. Barry Johnson

Wide field of view three-mirror telescopes having a common optical axis

Two coincident-optical-axis, three-mirror telescopes have been designed that feature relatively low focal ratios (f/2.3 and f/3), unobscured optical aperture, large circular fields of view (6° and 8°), good resolution, flat field, reimaging with accessible field stop, Lyot or glare stop, effective stray light suppression, and ease of spectral filter integration. The design for the f/3 telescope with 8° field of view has been fabricated and validated using single-point diamond turned optics.

Ultraviolet imager for the International Solar Terrestrial Physics mission

Imaging of the earths auroral regions in the ultraviolet provides information on a global scale on the energy flux and characteristics of precipitating particles an on the composition of the atmosphere in which the energy is deposited. The authors report the design of an imager with 0.6-mrad angular resolution over an 8-deg field of view sampled with 39,500 pixels, yielding global auroral coherent imaging from above 6 R[sub E](Earth radii). High-performance filters provide spectrally pure measurements of four key far-UV (FUV) features, with 5 [times] 10[sup [minus]5] out-of-band rejection. Together with a solar blind intensified CCD detector, a net rejection of 10[sup [minus]9] of all out-of-band emissions is achieved. The optical design comprises a three-mirror f/3 system that yields a noise equivalent sensitivity of 10 rayleighs (R) for a 37-s frame rate. The intrascene and interscene dynamic ranges are 1,000 and 10[sup 5], respectively. The optical surface microroughness is less than 2 nm, providing exceptionally low light scattering characteristics, allowing simultaneous observations of very weak and bright emissions. The imager should provide about two orders of magnitude improvement in performance over previous designs.

All-reflective four-element zoom telescope: design and analysis

The design process for an all-reflective zoom telescope is presented. Special consideration is given to the development of the starting configuration and the subsequent optimization process. The non-traditional optimization route utilized as a result of the unusual pupil characteristics of such an all-reflective zoom system is examined. Results of the design are presented.

On The Validity And Techniques Of Temperature And Emissivity Measurements

The measurement of temperature and emissivity of objects is of significant importance in science, industry, and other areas. A lingering question regarding the validity of temperature and emissivity values determined using two-color ratio radiometric measure-ments has been answered. Although generally valid, certain spectral-band configurations can produce ambiguous results. General guidance in the selection of the spectral bands to maximize the sensitivity of the ratio with respect to temperature is presented. Several techniques to measure the emissivity of materials are discussed along with representative experimental results.

Temperature measurement validity for dual spectral-band radiometric techniques

The measurement of the temperature of objects by remote means is important in science, industry, and other areas. A technique often employed is ratio radiometry, in which the temperature of the object is related to the ratio of the radiometric signals derived from each of two measurement spectral bands. A lingering question as to whether this technique is valid for determining temperature is answered. Although the technique is generally valid, certain spectral-band pairs can produce ambiguous results, namely, the same ratio can be obtained by looking at two objects, each at a particular, yet different temperature. Ambiguities occur only for spectral-band arrangements in which one spectral band is completely contained within the other. Examples are presented to illustrate this finding.

Design and fabrication of the all-reflecting H-Lyman alpha coronagraph/polarimeter

We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at 215.7 A - the neutral hydrogen Ly-alpha line. It is shorter and faster than the telescope which produced solar Ly-alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-alpha line is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman-alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings to optimize the reflectivity and polarization properties at 1215.7 A. We describe some of the solar imaging results obtained with the MSSTA Lyman-alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman-alpha Coronagraph/Polarimeter.

Relative Merits Of The 3-5 µm And 8-12 µm Spectral Bands

The two most common spectral bands used in the thermal infra red are the 3-5 μm and 8-12 μm bands. For years, substantial controversy has occurred over which of these spectral bands has the greater merit. A qualitative approach to address this question is presented.

What's different about ultraviolet and infrared optics?

The design and fabrication of components comprising ultraviolet and infrared optical systems require the same general engineering considerations to be given. In actuality, a variety of significant differences exist in the magnitude of considerations for optical systems in these two spectral regions. Among these are the optical materials available for use, surface finish, mechanical and optical fabrication techniques, housing and mounting methods, alignment and test, and cost. This paper contrasts and compares the practical issues facing the designer, fabricator, and assembler dealing with optical systems for the ultraviolet and infrared spectrums.

Instrumentation to measure the near-IR spectrum of small fruits

The acousto-optic tunable filter (AOTF) was demonstrated to be an effective and economical means for implementing a compact ( field deployable ) near-infrared Acousto-Optical Spectrometer (AOS) for quality assessment of small fruits. The design and construction of this device including design limitations and problems are presented. The characterization of the AOTF and the AOS system design address the areas of radiation source selection optical alignment optical design signal detection computer control and system testing. This work confirmed the operating specifications and limitations of the AOTF as described by the manufacturer.

A historical perspective on understanding optical aberrations

The design and development of today’s optical systems were made possible by a theoretical understanding of optical aberrations. Although the subject is still evolving, serious work spans almost four centuries. In this paper, a historical summary of the development of the understanding of optical aberrations is presented by relating the contributions of numerous individuals. The major events and discoveries are also presented in a time-line format on a century by century basis to allow a rapid overview.