Balloon telescope optics

Synthetic spectra: a tool for correlation spectroscopy

We show that computer-generated diffractive optical elements can be used to synthesize the infrared spectra of important compounds, and we describe a modified phase-retrieval algorithm useful for the design of elements of this type. In particular, we present the results of calculations of diffractive elements that are capable of synthesizing portions of the infrared spectra of gaseous hydrogen fluoride (HF) and trichloroethylene (TCE). Further, we propose a new type of correlation spectrometer that uses these diffractive elements rather than reference cells for the production of reference spectra. Storage of a large number of diffractive elements, each producing a synthetic spectrum corresponding to a different target compound, in compact-disk-like format will allow a spectrometer of this type to rapidly determine the composition of unknown samples. Other advantages of the proposed correlation spectrometer are also discussed.

Dispersive correlation spectroscopy: a study of mask optimization procedures

A procedure has been established to obtain the design parameters of the masks used in dispersive correlation spectrometers. The SNR equations are used to derive the mask equations. These are later solved for some simplified band models, and the obtained parameters are used as the initial values in an iterative program which determines the final design parameters. The calculations can be performed for various backgrounds and instrumental line profiles in order to achieve the best compromise for the detection of pollutants, and other trace gases, in the atmosphere.

Achromatic doublet lenses for infrared radiation

The indices of refraction and partial dispersions for the chlorides, bromides, and iodides of sodium, potassium, and cesium are suited for making diffraction-limited achromatic doublet lenses that are useful in infrared instruments. This paper describes the four best combinations (from seven materials). Together they cover the infrared over the range lambdalambda 1.5-38 micro. The performance of two lenses of optimized design (KBr-NaCl) is displayed by spot diagrams and test results. Applications of lenses, rather than mirrors, for compact optical systems are discussed.

A balloon-borne infrared coronagraph

A stratospheric balloon-borne coronagraph operating at wavelength 2.2 micro has been successfully flown in order to observe the outer solar corona. The system employed external occultation with three straight edges, and the Lyot portion was axial. Scanning of the corona was accomplished through rotation of the rear Lyot section about a diameter of the primary objective lens. A description of the origins of stray light in the instrument is given, and measurements at wavelengths 0.5 micro, 0.8 micro, and 2.2 micro presented. A wavelength dependence of the scattered light from the objective lens is deduced. Some details of the detection system and solar tracking are discussed.