Two-mirror Optical System Research Articles

Research on precision calibration technology for focusable off-axis two-mirror optical system

Research on precision calibration technology for focusable off-axis two-mirror optical system

Two-mirror aerial mapping camera design with a tilted-aplanatic secondary mirror for image motion compensation.

The optical compensation method is a promising method to compensate the image motion by driving the optical element of the system. However, the tilt motion of the optical element could induce the degradation of the image quality. Based on the Nodal Aberration Theory (NAT), this paper proposes a novel optical image motion compensation design with a secondary tilt-aplanatic two-mirror optical system (STATOS), which achieves the insensitivity on the image quality of the optical system. First, the properties of coma-free pivot point depending on the location of stop at primary mirror or secondary mirror have been analyzed respectively. Then the calculating method about construction parameters in terms of STATOS is developed. Further, the maximum tilt angle of secondary mirror could be solved using NAT under ordered specific restriction. Finally, a prototype is designed with SM-tilting result of MTF value maintain above 0.32 at the cut-off frequency of detector, where the principal distance could remain stable and the changed distortion is better than 0.03%. A test flight has been carried out to prove the desired results and feasibility of STATOS used in an aerial mapping camera.

Efficient misalignment calculation for two-mirror optical systems based on wavefront aberrations in a single field of view

Computer-aided alignment (CAA) is a key technology for improving the assembly efficiency and performance of optical systems. However, because of the coma-free pivot point in two-mirror optical systems (TMOSs), the wavefront aberrations from multiple fields of view (FoVs) are required to compute misalignments, and this is not practical. Therefore, misalignment-caused wavefront aberrations were investigated based on the nodal aberration theory, and an analytical aberration computation model for TMOSs was derived. Based on this, an efficient misalignment calculation method based on single-FoV aberrations that introduces known misalignments was proposed and tested by conducting Monte Carlo simulations using the Hilbert telescope. The results showed that micron-level precision can be achieved for the aberration and misalignment calculation without any measurement noise and that a greater number of introduced misalignments can decrease the effect of measurement noise, thereby verifying the effectiveness of the proposed model and method. The findings of this research will open a new direction in CAA by introducing the misalignment rather than the FoV.

Misalignments Computation of a Two-Mirror Optical System based on Modified Merit Function Regression Method

The computer-aided alignment (CAA) is a key technology to align a precision optical system, which is generally a difficult and laborious work. However, many methods proposed has a weak point in that they cannot calculate the misalignments accurately if there are figure error in mirrors. In order to solve this problem, a new modified merit function regression (MFR) is developed, which can compute the misalignments even if the effect of figure error. Misalignments computation based on the traditional and modified MFR are tested in a typical two-mirror optical system, experimental results shows the correctness of modified MFR and its high calculation accuracy.

Concept of a Facility of Neutron Radiography and Tomography at the Research Reactor WWR-K in Almaty, Kazakhstan

At the research reactor WWR-K (Institute of Nuclear Physics, Ministry of Energy, Almaty, Kazakhstan) work on the creation of a new experimental facility for research using neutron radiography and tomography method has begun. It is planned that the facility will form a neutron beam with a cross section of 200 × 200 mm, with a characteristic parameter L/D of 130, using a vacuum collimator system. To obtain neutron radiographic images, a specially designed detector system based on a 6LiF/ZnS scintillation screen and a high-resolution high-sensitivity video camera with a rotated mirror will be used. To protect the video camera from radiation, a two-mirror optical system is proposed. The paper presents a schematic diagram and description of the main components of the experimental setup.

Off-axis two-mirror laser communication antenna designed using differential equations

In satellite laser communication technology, which is built between planets and between a planet and the Earth, the optical antenna is the key point. Thus, research on optical system design is important. The off-axis reflective system has no obscuration and hence possesses a high efficiency for energy transfer. This study proposes a novel method for designing a free-form off-axis reflective imaging system. This study also introduces differential equations that depend on Fermat’s principle and sine condition. Finally, a free-form off-axis two-mirror optical system was designed by using the differential equation method. This system includes one intermediate image plane, in which the field of view (FOV) is–5° to–4° in the y-axis and–1° to 0° in the x-axis. The modulation transfer function was greater than 0.7 at 50 lp/mm, and the efficiency of energy transmission was high. The free-form off-axis two-mirror optical system involves a wide range of application prospects in the optical antenna used in the satellite laser communication systems. Moreover, the design method that used differential equations was proven simple and effective.

One-mirror and two-mirror three-dimensional optical scanners--position and accuracy of laser beam spot.

This article presents several fundamental formulas for ray tracing in optical systems used in 3D optical scanners. A procedure for numerical modeling of one-mirror and two-mirror optical systems is presented, and the calculation of positioning and accuracy of the laser beam spot in a detection plane is carried out. Finally, a point position and accuracy depending on a transit time is evaluated.

Evidence that convergence rather than accommodation controls intermittent distance exotropia

This study considered whether vergence drives accommodation or accommodation drives vergence during the control of distance exotropia for near fixation. High accommodative convergence to accommodation (AC/A) ratios are often used to explain this control, but the role of convergence to drive accommodation (the CA/C relationship) is rarely considered. Atypical CA/C characteristics could equally, or better, explain common clinical findings. Nineteen distance exotropes, aged 4-11 years, were compared while controlling their deviation with 27 non-exotropic controls aged 5-9 years. Simultaneous vergence and accommodation responses were measured to a range of targets incorporating different combinations of blur, disparity and looming cues at four fixation distances between 2 m and 33 cm. Stimulus and response AC/A and CA/C ratios were calculated. Accommodation responses for near targets (p = 0.017) and response gains (p = 0.026) were greater in the exotropes than in the controls. Despite higher clinical stimulus AC/A ratios, the distance exotropes showed lower laboratory response AC/A ratios (p = 0.02), but significantly higher CA/C ratios (p = 0.02). All the exotropes, whether the angle changed most with lenses ('controlled by accommodation') or on occlusion ('controlled by fusion'), used binocular disparity not blur as their main cue to target distance. Increased vergence demand to control intermittent distance exotropia for near also drives significantly more accommodation. Minus lens therapy is more likely to act by correcting overaccommodation driven by controlling convergence, rather than by inducing blur-driven vergence. The use of convergence as a major drive to accommodation explains many clinical characteristics of distance exotropia, including apparently high near stimulus AC/A ratios.

带有无光焦度校正板两镜系统的三级像差校正

带有无光焦度校正板两镜系统的三级像差校正

带有无光焦度校正板两镜系统的三级像差校正

带有无光焦度校正板两镜系统的三级像差校正

Adjustment of two-mirror centered optical systems using synthesized holographic optical elements

This paper discusses a method of adjusting two-mirror centered optical systems, based on the use of a point light source and a synthesized holographic optical element consisting of three axial synthesized holograms arranged coaxially on the common working surface of the substrate. An optical layout is presented for a device used as the basis for implementing the principle of adjusting the mirrors of two-mirror optical systems. The method can be used to adjust mirror and mirror-lens systems based on both axisymmetric and off-axis aspheric mirrors whose reflecting surfaces can be of second and higher orders.

Optical design of freeform two-mirror beam-shaping systems

The problem of design of a two-mirror optical system for reshaping the irradiance distribution of a laser beam in a prescribed manner is considered in the geometrical optics approximation. The presented design equations are derived in a rigorous manner and are applicable to two-mirror optical systems not limited to radiance profiles and beam cross sections that are rotational or rectangular symmetric. The resulting mirrors are free-form surfaces not restricted by a priori constraints. Moreover, the presented approach shows also that even in the general case two different designs are available for the same data. In one of these designs the first mirror is always concave and the second is convex, while in the second design the resulting mirrors may be neither convex nor concave. Since, in general, the surface mirrors are aspherical, the availability of a design with convex and concave mirrors is particularly important for fabrication.

Merit function regression method for efficient alignment control of two-mirror optical systems

The precision alignment of high-performance, wide-field optical systems is generally a difficult and often laborious process. We report a new merit function regression method that has the potential to bring to such an optical alignment process higher efficiency and accuracy than the conventional sensitivity table method. The technique uses actively damped least square algorithm to minimize the Zernike coefficient-based merit function representing the difference between the designed and misaligned optical wave fronts. The application of this method for the alignment experiment of a Cassegrain type collimator of 900mm in diameter resulted in a reduction of the mean system rms wave-front error from 0.283 lambda to 0.194 lambda;, and in the field dependent wave-front error difference from +/-0.2 lambda to +/-0.014 lambda in just two alignment actions. These results demonstrate a much better performance than that of the conventional sensitivity table method simulated for the same steps of experimental alignment.

Two-mirror optical systems with multiple reflection from the spherical principal mirror

Two-mirror optical systems with multiple reflection from the spherical principal mirror

Phase effects owing to multilayer coatings in a two-mirror extreme-ultraviolet Schwarzschild objective

The aberrations of a multilayer-coated reflective Schwarzschild objective, which are influenced both by mirror surface profiles and by multilayer coatings, are evaluated with a phase-shifting point diffraction interferometer operating in the extreme ultraviolet. Using wave-front measurements at multiple wavelengths near 13.4 nm, we observed chromatic aberrations and wavelength-dependent transmission changes that were due to molybdenum-silicon multilayer coatings. The effects of chromatic vignetting due to limited multilayer reflection passbands on the imaging performance of the Schwarzschild optic are considered. The coating characteristics extracted from the interferometry data on the two-mirror optical system are compared with previously reported coating properties measured on individual mirror substrates.

Two-mirror unobscured optical system for reshaping the irradiance distribution of a laser beam

The design of a two-mirror optical system for reshaping the irradiance distribution of a laser beam is presented. The second mirror is decentered relative to the first to eliminate the obscuration inherent in an axially symmetric design. A geometric-optics approach is used to derive a set of equations that describe the surface figures of each of the mirrors. (In general, the mirror surfaces are not rotationally symmetric.) The special case of a system to convert a Gaussian input beam into a uniform output distribution is considered. The expressions for the surface figures are evaluated numerically for several specific systems to provide illustrative examples. It is observed that in some cases rotationally symmetric aspheres may be used to construct the beam-shaping system.

Reflective optics for irradiance redistribution of laser beams: design

The output irradiance of a typical unstable resonator with circular symmetry has a central obscuration and is peaked near the obscuration. A method is presented for designing two-mirror optical systems to convert this beam into a beam of arbitrary obscuration ratio and more uniform irradiance. A method is also given for analyzing the alignment sensitivity of such a system. An example shows that useful irradiance redistributions can be achieved with alignment sensitivities comparable to ordinary Cassegrain systems.