Optical: systems and elements – Holographic system or element – Having particular recording medium
Reexamination Certificate
2000-09-07
2003-09-23
Juba, John (Department: 2872)
Optical: systems and elements
Holographic system or element
Having particular recording medium
C359S001000, C359S900000, C349S193000, C349S201000, C430S001000
Reexamination Certificate
active
06624915
ABSTRACT:
FIELD OF THE INVENTION
The preferred embodiments of the present invention relate to a process of two-photon induced photopolymerization for the formation of microstructures. More particularly, the preferred embodiments of the present invention relate to holographic two-photon induced photopolymerization (“H-TPIP”) in the construction of reflection and transmission holograms.
BRIEF SUMMARY OF THE INVENTION
Summary of the Problem
Molecular excitation via the simultaneous absorption of two photons can lead to improved three-dimensional (“3D”) control of photochemical or photophysical processes due to the quadratic dependence of the absorption probability on the incident radiation intensity. This has lead to the development of improved 3D fluorescence.
Recently, the ability to fabricate 3D optical storage devices and ornate 3D microstructures has been demonstrated using two-photon induced photopolymerization (TPIP). This method requires sequential scanning of a series of extremely short (100-150 fs), high-peak-power (≧100's &mgr;W) laser pulses in a tightly focused single-beam geometry to cross the TPIP initiation threshold.
Others have sought to intersect two or more separate beams within a 3D photoactive material to induce simultaneous two-photon absorption exclusively within their respective intersection volumes. More recently, still others have sought to create three dimensional optical storage devices using a single highly focused beam to induce simultaneous two-photon excitation within one spatial region. Using this technique, arrays of photo-induced structures are then made by serially scanning the focused beam within a three dimensional photoactive material.
The microfabrication of microelectromechanical systems (MEMS) for biotechnology applications (bioMEMS) is a rapidly growing field. High-throughput DNA analysis is of central importance due to the many applications including, for example, chemical/biological weapons (CBW) defense. Bioagent detection, e.g., anthrax spores, can be accomplished quickly and specifically using high-throughput DNA analysis based on standard techniques like polymerase chain reaction (PCR). For industry, high-throughput DNA analysis has implications for the Human Genome Project.
The industrial challenge of completing the Human Genome Project is based on miniaturization technology which allows for more DNA to be analyzed in dramatically shorter time frames (minutes versus hours).
To this end, there is currently a push towards a lab-on-a-chip which makes use of conventional photolithography and laser induced fluorescence imaging to create a microfluidic plate containing site specific functionality. Microfluidic chips have the potential to synthesize thousands of individual molecules in microchannels in minutes, instead of the hours or days traditionally needed. The target species lab-on-a-chip microfluidic experiments are DNA, pathogens, toxins, cell-specific, and protein-specific. Various exemplary applications for utilization of lab-on-a-chip microfluidic experiments are environmental monitoring, biological warfare detection, cell sorting, protein separation, medical diagnostic, filtration, etc. The basic premise is to fabricate microfluidic channels, which have some form of functionality associated with individual pathways or micro-reservoirs. This functionality can take the form of enzymes, antibodies, DNA binding proteins, catalytic agents, etc. The injection of a sample, usually on the order of picoliters, flows through the microfluidic plate, causing reactions in various channels or test sites. The unreacted or unbound material is rinsed away. Computer readout of the various reactions is accomplished by tagging the individual reaction sites with a fluorescence dye. A laser is scanned through the plate and fluorescence imaging is used to map the reacted sites.
The manufacturing of these microfluidic chips relies primarily on conventional photolithography. Functionality is imparted after the fact by infusing the chip with some sort of polymer having the incorporated reactive species within it. Various masks are used to isolate different reactive species to specific areas of the chip. Thus, construction of the chips can take a good deal of time. Also, integration of the microlabs into the outside world is a significant challenge, while laser scanning is fine for laboratory work, portable or smaller versions would require something better. Attempts have been made to fiber couple these systems to a portable computer, but this technique has met with little success. A possible solution to that particular problem is being addressed through the conventional multiphoton laser ablation and micro-machining technologies. Industry leaders such as Clark MXR, SpectraPhysics and university collaborators are using high intensity lasers to ablate a channel and to form a waveguide perpendicular to the channel. While this would allow direct fiber optic coupling to the channel, the process is still a serial process, has low resolution, and does not give the elegant finesse required for more complex multidimensional forms.
The ability to reproduce naturally occurring micro and nano-structures is also highly sought after. One major roadblock to being able to image and reproduce these bio-structures is the fact that many conventional imaging technologies utilize ultra-violet wavelengths. Ultra-violet wavelengths are destructive to biological tissue.
Recent advances in conducting polymers to be used as an inexpensive supplement to conventional semiconductor, metallic, and ceramic components, have outpaced the corresponding fabrication techniques, which still rely upon one-photon polymerization and photolithographic technologies. Consequently, fabrication techniques for electronic circuits which utilize these conducting polymers are struggling to keep up with improvements to the conducting materials.
Also, the demand for low cost, high capacity data storage is increasing in both the military and the commercial sector. In the commercial sector, demand is primarily driven by the increasing digital format in the expanding computer, entertainment, and medical diagnostic areas. The military demand is primarily dictated by the data storage for hyperspectral data/image gathering and simulations. In short, increased optical data storage capacity and speed will be driven by going into the third dimension and by increasing multiplexing (spatial or frequency).
By taking advantage of all three dimensions instead of a planar storage configuration, data storage capacities of 1-10 terabits/cm
3
are theoretically possible in the visible spectrum (P. J. Van Heerden,
Appl. Opt
., 2, 393-400 (1963)). Viewed mostly as a secondary or tertiary (archival) memory device, optical data storage is characterized by huge amounts of low cost per megabyte storage capacity with moderate access times (longer than 10 ms). Despite the low cost per megabyte capacity, storage could easily represent the single most expensive element in such large-scale operations as super computing. Several technologies have been considered for 3D data storage including layered 3-D optical storage, holographic data storage, persistent spectral hole burning, and near-field optical storage.
Because persistent spectral hole burning requires cryogenic temperatures and near-field optical storage has stringent requirements on the placement of the optical probe, their near-term commercialization is questionable. However, layered 3-D optical storage is a logical extension of current optical disk technology in which the information is simply stacked. The volume resolution (i.e., Mb/cm
3
) of these techniques is based on the precision of the read/write optics, the wavelength, and the resolution of photoactive media.
Further, the infrastructure of the telecommunication, display, and future computing industries rely heavily on the ability to switch information rapidly and with high contrast between two or more different states. The recent development of switchable diffractive elements using, e.g., polymer-dispersed liqui
Baur Jeffery W.
Bunning Timothy J.
Denny Lisa R.
Kirkpatrick Sean M.
Natarajan Lalgudi V.
Juba John
Kilpatrick & Stockton LLP
Science Applications International Corporation
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