1. Introduction

As optical systems become more complex and packaging requirements more severe and multi-dimensional, proper alignment becomes more challenging. Yet with current improvements in the manufacture and measurement of optical surfaces to nm levels, alignment is one of the few remaining opto-mechanical aspects of optical system manufacture and assembly where improvement in optical performance can be made. There are four approaches to aligning optical systems. These will be described and the advocated method illustrated by examples.

The preferred alignment method overcomes most of the difficulties of traditional methods but requires a new way of thinking about alignment. The method also requires alignment considerations must be studied immediately after the optical design is complete so that the necessary opto-mechanical datums can be incorporated into the mechanical design of the optical system cell, chassis or lens bench.

1. Introduction

It is common to think of computer generated holograms (CGH) as artifacts for testing aspheres but they can also be used as general calibration artifacts and fixtures for the alignment and test other more conventional optics. We show how simple Fresnel zone patterns can be created to simulate centers of curvature or axes in space with dimensional precision associated with microlithography. These centers of curvature and axes can then be located in space to similar sorts of precision with an autostigmatic microscope (ASM) or an interferometer.

Once the ASM is centered on the center of curvature, or axis, of the Fresnal zone pattern, a ball, or cylinder, respectively, of matching radius can be aligned to the ASM or interferometer to similar sorts of precision and physically attached to the CGH to serve as kinematic datums against or on which to mount other optical or mechanical components.

We then give an example of the fixture for the mounting of a rectangular lens element into a kinematically located frame so the two can be cemented together prior to inserting the bonded pair into an optical bench.

INTRODUCTION
On-machine metrology is particularly important for diamond turning and grinding as it is difficult to remount and align a part if it does not meet off-line inspection criteria. There is also the issue of tool wear; a process that started well may fail part way through the cut, and if tool replacement is needed, it is vital to know that before removing the part. A means of rapid, noncontact, in situ profiling and roughness measurement could improve the productivity of diamond tool machining.

Recently we first showed that diamond turning machines are sufficiently isolated that steady fringes can be obtained by simply setting a Point Source Microscope [1,2] equipped with an interferometric Mirau objective on the cross slide of a machine. Further, we demonstrated that the machine can be precisely driven to get temporally shifted fringes so that common algorithms can be used to obtain area based surface roughness measurements. This led to the question of whether essentially the same hardware could be used to rapidly profile diamond turned parts. We show via simulation that the answer is yes and that the approach can be implemented rather simply.

We first describe the PSM and its configuration as a Microfinish Topographer (MFT) by using interferometric data reduction software. Then we describe how this hardware is changed into a profiler by changing the light source and camera. Finally, we show how this hardware that we call a Non-Contact Profiler [3] (NCP) is used on a diamond turning machine to profile turned or ground parts in situ.

ABSTRACT

Introduction

• Need for reverse engineering
• Properties necessary for reverse engineering
• How to make necessary measurements
• How to calculate the paraxial properties
• Use of a spreadsheet for the solution
• Use of a lens design program to find a solution

Although the PSM is primarily an alignment instrument, it can also be used to determine the conjugates of parabolic and elliptical off-axis mirrors. By positioning the PSM at the sagittal and tangential foci of the mirrors, the conjugate distances of the mirror can be found using a laser range finder, for example. Knowing the sagittal and tangential radii of curvature (Rs and Rt), the vertex radius (Rv) is easily calculated. This information is used to verify that the mirror has been correctly manufactured and to aid in positioning the mirror in an optical system. Examples are shown of these steps.

ABSTRACT

An autostigmatic microscope is described and its uses explained. Then an adaptation of the original instrument is described that uses current technological advances in laser diodes and video displays to turn an old workhorse into a versatile optical test and alignment device. This paper illustrates applications that make use of the capabilities of the modern autostigmatic microscope outside the field of aligning optical systems such as using it as an electronic autocollimator, a check on the centration of the axes of molded optics and the measurement of the runout and wobble of precision spindles such as air bearings.