Fabricating 3D Microstructure and High-Resolution Imaging Using NI LabVIEW

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"In an ever-changing experimental physics environment, National Instruments hardware and the LabVIEW graphical programming language helped us conveniently develop control systems for microfabrication and imaging. We easily modified interfaces and programs, which we developed much quicker than some earlier work in the line-by-line code C."

- Dr. Martin Straub, Centre for Micro-Photonics, Swinburne University of Technology

The Challenge:
Controlling a piezoelectric nanopositioning stage for 3D microstructure fabrication and photon-counting optical tomography.

The Solution:
Using National Instruments LabVIEW software to develop an efficient 3D scanning program with a convenient graphical user interface.

Mr. Michael Ross Vanner - Centre for Micro-Photonics, Swinburne University of Technology
Dr. Martin Straub - Centre for Micro-Photonics, Swinburne University of Technology
Prof. Min Gu - Centre for Micro-Photonics, Swinburne Univerisity of Technology

3D Polymer Microstructure Fabrication and Low-Light Level Optical Tomography

Complex-shaped, 3D microstructures have recently received a significant amount of attention within, as well as beyond, the scientific community because of the promise they hold for exciting new applications in a variety of areas.

These structures may serve as mechanical or optical microdevices in micro environments or even nano environments. For instance, diagnosis or surgery inside the human body may become more efficient because of micromovers and pumps that can interact on the cellular level.

In addition to mechanical characteristics, these structures can be fabricated to have interesting optical properties and can be used as photonic devices in such applications as telecommunications and optical information processing.

We fabricate these structures by scanning a liquid of monomers and oligomers through a high-intensity laser focus, where the polymerization reaction solidifies the material, building a solid polymer structure along a preprogrammed pathway.

Observing the fluorescence of a sample in 3D at high resolution permits researchers to obtain information in many experiments, from biology to physics. Low-light-level applications – for example, observing processes in living cells – are particularly challenging. We used National Instruments hardware and software to fabricate these photopolymer microstructures.

Our solution uses a photomultiplier tube to collect the light and generates pulses upon photon-capture events. We use a National Instruments PCI-6602 counter/timer, which has a sufficiently high count rate, to count pulses. We then use NI LabVIEW to process count rates to generate images of the object under scrutiny.

We use an NI PCI-DIO-96 digital I/O board to communicate positioning data to the stage controller and provide trigger signals for the laser shutter, and we use an NI PCI-GPIB board to transfer command strings. With the PCI-6602 counter/timer, we can count pulses from a photon-counting photomultiplier simultaneously with the translation stage movement.

Digitally Controlled Nanopositioning Using the PCI-DIO-96

Custom-built LabVIEW software running on the control PC communicates with a Physik Instrumente E710 digital translation stage controller and a mechanical laser shutter. This involves both ASCII and binary data, which is sent via the PCI-GPIB and the PCI-DIO-96 boards, respectively. We use the ASCII commands to initialize the controller and set experimental parameters such as the scanning velocity. The positional information is sent as 16-bit digital data, along with three address lines and three control lines, which communicate to the controller via the PCI-DIO-96.

We configure the board ports as input/output as necessary during the beginning of the program. These settings remain unchanged for most experiments. To issue a movement command, we change the signal levels on the control lines according to specific timing diagrams to latch the address of the axes and the coordinates. The PCI-DIO-96 board also controls the laser shutter, which opens or closes given a TTL input, controlling exposure of the sample to the laser light irradiation. This process must be regular and reliable or microstructures strongly degrade.

3D Imaging at Low-Light Levels Using the PCI-6602 Counter/Timer

A more sophisticated version of our nanopositioning program combines 3D movement capability with synchronized acquisition of fluorescence photon count rates measured at each point, or pixel, for a predetermined dwell time. We use the first three of eight counter channels on the PCI-6602 to count photon-capture TTL pulses, provide an accurate pulse train, and monitor movement latching. This hardware gating pulse train with a period of the pixel dwell time gives consistent dwell time quoted with accuracy to the nearest microsecond. This provides an external source to trigger movement, eliminating software delays. The PCI-DIO-96 polls an optimized integer number of the gating periods, depending on the pixel size, to provide a precise delay to complete the movement.

Because scans often involve many thousands of points, minimizing the processing time for each point becomes essential, so we employ the PCI-6602 internal buffers. Both buffers operate in a cumulative manner and need to be processed at each scan completion. The first of these buffers stores the fluorescence count rates, while the other verifies that movement occurred during the correct gating period, ensuring the observed count rates correspond to correct translation stage positions.

We implement three scanning techniques – count rate acquisition in a line trace, raster planar scanning, and a volume scan. We display results on a scatter plot or color intensity chart as well as write them to data files for later manipulation.

In an ever-changing experimental physics environment, National Instruments hardware and the LabVIEW graphical programming language helped us conveniently develop control systems for microfabrication and imaging. We easily modified interfaces and programs, which we developed much quicker than some earlier work in the line-by-line code C.

For more information, contact:

Prof. Min Gu

Centre for Micro-Photonics

Faculty of Engineering and Industrial Sciences, Mail 38

Swinburne University of Technology, PO Box 218

Hawthorn, Victoria 3122


Tel: +61-3-9214 4315 / +61-3-9214 8776

Fax: +61-3-9214 5435

E-mail: mgu@swin.edu.au


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