In contrast to conventional optical systems, which are optimized for wavelength-independent imaging, hyperchromats aim for strongly wavelength-dependent focal lengths. In this contribution, the design parameters of hyperchromatic two-lens optical systems were derived that provide strong axial color splitting expressed by extremely low equivalent Abbe numbers. These systems have been investigated for compositions of either pure refractive or all diffractive lenses, as well as hybrid configurations thereof. First, lens doublets made of cemented elements are considered and the variables affecting the equivalent Abbe number of the system are investigated. In particular, the influence of the focal lengths of the individual lenses and the Abbe numbers of the selected lens materials are taken into account. The best parameter-sets were determined by paraxial numerical simulations for different cemented configurations. To ensure a simple implementation, especially to avoid exotic or potentially harmful materials, only readily available inorganic standard glasses were considered. In the next phase of this investigation an air gap was inserted between the two lenses, which is an additional influence parameter on the equivalent Abbe number. Following the paraxial considerations, selected two-lens configurations were transferred to the non-paraxial domain and refined using optical design software, also taking aberrations into account. To further reduce achievable equivalent Abbe numbers, an aspherical surface was introduced to compensate for spherical aberrations. Finally, for the refractive doublets an equivalent Abbe number of 2.4 was achieved, which corresponds to only 12% of the smallest Abbe number of the selected materials. This result was even surpassed by the hybrid hyperchromat, resulting in an extraordinary minimum equivalent Abbe number of -0.6 that is more than five times smaller than the Abbe number of diffractive lenses.
Echelle-inspired cross-grating spectrometers try to combine the high performance of classical Echelle spectrometers and the small footprint of compact line-grating spectrometers. Therefore, a cross-grating is used which is a superposition of two perpendicularly oriented line gratings in a single element. Highly resolved, but overlapping, diffractions orders are created by the main grating, which are separated by the cross-disperser. This powerful approach is connected to different challenges concerning the optical design, the fabrication of the cross-grating and implementation of the device. These challenges are addressed by a compact and rigid double-pass design, which utilizes the same refractive elements for collimation of the incoming beam and focusing of the diffracted light on the detector. This contribution gives an overview on the design and focusses on the implementation of the spectrometer. This includes on one hand the mounting of the cross-grating and the refractive elements in a rigid objective group and, on the other hand, the adjustment of the objective to the entrance fiber and the 2D detector. Furthermore, the implemented and calibrated instrument allows to conduct several validating experimental tests in order to proof the working principle. The spectrometer addresses a spectral range from 400 nm to 1100 nm and reaches a resolving power of 300 with an entrance pinhole diameter of 105 μm. An even higher resolving power of more than 1000 is reached with a reduced pinhole diameter of approximately 5 μm.
This contribution addresses an alternative lithographic technique for the tailored fabrication of rotationally symmetric meso- and microscale optical components. A variable ring-shaped light distribution is created by an axicon-pair based zoom-concept and can be used for the manufacturing of single optical components and array elements as well. First, design considerations of the basic axicon system and the achievable system characteristics are discussed. In particular, minimum and maximum ring diameter depending on axicon angle variations and displacement distance of employed axicons as well as potential deviations from the telecentricity condition are considered. Additionally, further aspects concerning the system implementation are presented, e.g. the achievable resolution which is dependent on the entrance pinhole. Finally, the performance of the system is presented by demonstrating the fabrication of exemplary meso- and microscale structures.
Pushbroom hyperspectral imaging systems require relative motion with respect to the target for hyperspectral data acquisition by means of spatial scanning, which increases the equipment cost and limits the application scenarios. We address this by introducing a pushbroom system with an internal line-scanning unit consisting of a slit aperture mounted on a piezoelectric linear motor. Different slit positions have tilted incidence angles at the grating, resulting in shifts of diffraction patterns relative to the imaging sensor. We demonstrate a method to compensate this shift by using a rotating arm controlled by a stepper motor to reposition the camera based on slit position.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.