PBJacquemin .com. Telescope Beam Expanders, Ritchey-Chretien, Schimdt-Cassegrain, WFOV Isoplanatic, and Aspheric Optics.
Systems Engineer
Peter B. Jacquemin
Email Peter B. Jacquemin

Project and Research Descriptions
Telescope Optics and Beam Expanders

Project and Research Descriptions: | Applied Optics | Microscope | Telescope | Scanning Mechanisms | Target Acquisition |
| Acoustics | Luggage Scanning | Feedback Controls | Image Processing | 3D Virtualization | Holographic Microscope |

Telescope Optics and Beam Expanders
  • Ritchey-Chretien and modified Schmidt-Cassegrain telescopes
  • Custom off-axis parabolic three mirror design beam expander
  • WFOV isoplanatic lens design with wide spectral band and low f-number
  • Spherical and aspheric (hyperbolic & elliptic) lens designs

The three-mirror beam expander uses off-axis paraboloid surfaces. The x16 beam expander has a 0.5 FOV and provides diffraction limited optical resolution, but is difficult to align. The focal point provides a stationary entrance and exit pupil which is important for scanning and beam direction stabilization with beam steering mirrors.

The single lens shows an off-axis focal point shift due to translating a beam across the lens aperture. These optical aberrations adversely affect optical resolution and are corrected using a compound lens that I have designed as shown in the following figure.

Insert figure and text below between line "More advanced designs are available that provide higher optical resolution and lower aberrations" and figure titled "16th Order Polynomial Curvefit to Plano-Convex Asphere"

The incident angle on the lens surface and refractive index of the glass bends the rays across the aperture to the focal point. The glass retards the phase of the ray which is a function of wavelength, refractive index and path length through the glass. As the wave propagates along each ray path they reinforce or cancel at the focal depending on the relative phase. This is the principle of diffraction where a wave interferes with itself based on the wave passing through the center of the aperture and the diffraction from the edges of the aperture. A pinhole camera has excellent focal depth, dynamic contrast, and low aberrations which is based on the principle of diffraction and the wave energy of light interfering with itself at the focal plane.

The Wide Field-of-View (WFOV) isoplanatic lens is designed for constant focal length across the field or entrance angle. The blur spot size remains constant and the displacement on the focal plane is linearly proportional to entrance angle. This reduced field curvature design reduces pincushion and with proper selection of optical glass the spectral bandwidth can be extended as well. The f-number can also be reduced for the optical aberrations to match a singlet or doublet lens configuration. More advanced designs are available that provide higher optical resolution and lower aberrations.

The elliptic aspheric lens provides high optical resolution at extremely low f-number such as f/0.73 along with low off-axis coma aberrations, but is more difficult to manufacture than a spherical lens. A phase plate can be added to the back surface to align all the rays across the aperture for diffraction limited optical resolution at a particular field angle. Adaptive optics would be required to maintain diffraction limited optical resolution for a varying field angle. In general, diffraction limited resolution can be approached when the f-number is large. An aspheric lens can be duplicated with multiple spherical lenses using the Wollaston landscape lens and a meniscus lens.