A Shack-Hartmann wavefront sensor (SHWS) uses a lenslet array to sample incoming wavefront on an image sensor,
which is usually a Charge Coupled Device (CCD). By measuring the shift of centroids on CCD compared to reference
spots, wavefront profile is reconstructed and therefore test surface shape is revealed. There are various factors that affect
the performance of SHWS. In order to study how and to which extend does each factor affect reconstruction result, we
established a simulation platform for SHWS in MATLAB. Through this platform, detailed properties and affecting
factors were analyzed. Based on the system-oriented platform, we obtained some interesting findings, which are very
important in the design of S-H wavefront sensors. In this paper, the performance-affecting significance of the key
properties of the light beam, the diverging angle, the intensity distribution, and the intensity of the light beam, is
simulated, analyzed and concluded. The simulation results are useful guide for the selection, design and preparation of
the sensing light beam.
The misalignment of a particular optic in lens assembly will induce aberrations and deteriorate the performance. For the
purpose of failure analysis, there are requirements from optic manufactures for the development of measurement tool to
address the misaligned element. This paper presents a method for the quantitative measurement and analysis of
misalignment in lens assembly, which may figure out the misaligned element and its misalignment factors. Since there
are several optical elements in lens assembly, and there are different misalignments, such as decenter, tilt etc, a multiparameter
tool need to be employed in the analysis. Wavefront can be expressed with Zernike polynomials, which are
selected for the analysis. We choose a positive lens assembly with four elements for the study. A point light source is
placed in the front focus point of lens assembly; the collimated emergent wavefront is analyzed with Zernike
polynomials. We use Zeemax to simulate the propagation of wavefront, calculate Zernike coefficients correspondent to
various misalignment. The results show there is a group of Zernike polynomials correspond to each misalignment. Each
polynomial increase/decrease progressively against the magnitude of misalignment. It is difficult to tell the misalignment
only by the analysis of Zernike coefficients. To further address the misaligned elements, we present a concept - the
contrast value of Zernike coefficients, which is a series of constant even though the magnitude of misalignment changes.
The method and procedure is presented to measure the contrast value with the employment of dual directional wavefront
A measurement and imaging system has been developed for in-line continuous measurement of live, unmodified, human
embryonic stem cells (hESC). The measurement will not affect cell growth, structure, sterility and suitability for clinical
use. The stem cell imaging system (SCIS) can be used to support the optimization of automated stem cell growth for invitro
study and for high-volume bio-manufacture. This paper present the experimental and analysis for the optimization
of system parameters. A non-linear lighting is developed to obtain a clear images. The individual cluster can be traced
from day one to day two. The whole system is calibrated with measurement microscope and haemacytometer. The
measurement accuracy is better than 90%.
When wavefront is reflected by a surface, the information of the surface profile is carried by the reflected wavefront.
Measure the wavefront can extract the profile information. There are different kinds of pre-defined surface profile with
various dimensions. While the size of particular wavefront sensor is fixed, the measurement range is limited. The design
of optical system to bridge the work piece and wavefront sensor is critical. This paper presents a platform for the
guidance of optical system design. The parameters of commercial available optical components are input to the platforms
and the propagation of reflected wavefront is simulated. The relationship of part profile and the measurement wavefront
is provided. The discussion is focused on the 2f+2f system for surface flatness measurement. The measurement of
aspherical surface is also presented. Shack-Hartmann wavefront sensor (SHWS) is selected due to its simple structure,
insensitivity to vibration etc, which is suitable for in-line application. Optical system is designed with the guidance of
simulation platform. The experimental results shows the 2f+2f system is compatible to misalignments, can be used to
monitor the deformations of parts. The measurement of aspherical surface is also presented with the comparison of
Shack-Hartmann Wavefront Sensor (SHWS) recently has been extensively researched for optical surface metrology due
to its extendable dynamic range compared with the interferometry technique. In our institute, we have developed a
digital SHWS by adopting a programmable Spatial Light Modulator (SLM) to function as a microlens array and replace
the physical one in the traditional configuration of this sensing system. In this paper, we proposed to use the developed
system for the relative measurement of toroidal surfaces, which are widely used in many optical systems due to their
unique optical features of different curvatures in X and Y directions. An innovative idea to design the diffractive
microlens array implemented by SLM was presented to tackle the measurement challenge. This unconventional design
approach has a great advantage to provide different optical powers in X and Y directions so that focusing spots can be
formed and captured on the detector plane for accurate centroid finding and precise wavefront evaluation for 3D shape
reconstruction of the toroidal surface. A digital Shack-Hartmann Wavefront Sensing system with this unique microlens
array was built to verify the design concept, and the experimental results were presented and analyzed.
Since its emergence in the early 1970s, Shack-Hartmann Wavefront Sensing technology has been investigated and
explored world-widely by the researchers and engineers. However, there are few papers or reports to study the system
performance and key factors to affect the performance of a Shack-Hartmann Wavefront Sensor (SHWS), in this paper,
through experimental study of the system stability of a SHWS, it is found that the image sensor and detector, normally a
CCD, should be placed exactly at the focal plane of the lenslet array, otherwise it will bring in significant wavefront
measurement error. In order to improve the system performance, a special lenslet array with long focal range is designed,
and it is functioned by a spatial light modulator for sampling wavefront in a SHWS. Diffractive lenses with long focal
length range can provide pseudo-nondiffracting beams, and a long range of focusing plane. The performances and effects
of the modified SHWS with such a special lenslet array generated by a programmable SLM, are investigated, and the
experimental results show that the system stability and measurement repeatability are not sensitive to the sensing
distance, and can keep at a good level in a long range.
Transparent toughened glass panels are widely installed in high-rise buildings. There is a growing need for inspection to detect the presence of detrimental inclusions of Nickel Sulfide. These inclusions can cause toughened glass to shatter, possibly causing property damage or injury. Optical equipment has been developed which can detect the inclusions in-situ. Light is coupled into a glass panel and propagates along the glass by total internal reflection. An inclusion in the glass will cause the light to scatter. Once an inclusion is found, it will be observed at higher magnification and the detailed image will be processed. By the analysis of its key features, the inclusion type can be identified. The coupling medium is made of a transparent, soft and deformable material. The equipment can be attached to a glass panel by vacuum suction. The optical system can scan the whole glass panel with a constant force spring as anti-weight structure. The whole system is fast, convenient and highly effective. A patent has been filed for this apparatus.
This paper describes a multispectral liquid drop analyzer for liquid chemical and physical properties analysis. Liquid drops formed at the tip of a liquid head are measured in parallel by a fiber sensor and a capacitive sensor. The fiber sensor works as follows: multispectral light sources are injected into the drop through an optical fiber and the total internal reflections and absorptions are detected by a photodetector. By combining fiber and capacitive sensor outputs, a drop speed independent one-dimensional waveform (liquid fingerprint) is generated. Liquid surface tension, refractive index and di-electric constant can be estimated from the fingerprint. To compare two fingerprints, the sensor outputs are normalized to have the same unit of measurement and drop starting position. After that, a reference liquid based calibration is applied to correct of fingerprint distortion due to variations in environment conditions, such as changes in temperature and humidity. Finally, a normalized correlation algorithm analyses the fingerprint difference. The repeatability and sensitivity of the system are demonstrated using different liquid samples. On-line applications show that the analyzer is able to detect 2% change in alcohol density.