Browsing by Subject "optics"

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Application Of Detuned Laser Beatwave For Generation Of Few-Cycle Electromagnetic Pulses
(2004-12) Kalmykov, S.; Shvets, G.; Shvets, Gennady; Kalmykov, Sergey
An approach to compressing high-power laser beams in plasmas via coherent Raman sideband generation is described. The technique requires two beams: a pump and a probe detuned by a near-resonant frequency Omega < omega(p). The two laser beams drive a high-amplitude electron plasma wave (EPW) which modifies the refractive index of plasma so as to produce a periodic phase modulation of the incident laser with the laser beat period tau(b) = 2pi/Omega. After propagation through plasma, the original laser beam breaks into a train of chirped beatnotes (each of duration tau(b)). The chirp is positive (the longer-wavelength sidebands are advanced in time) when Omega < omega(p) and negative otherwise. Finite group velocity dispersion (GVD) of radiation in plasma can compress the positively chirped beatnotes to a few-laser-cycle duration thus creating in plasma a sequence of sharp electromagnetic spikes separated in time by tau(b). Driven EPW strongly couples the laser sidebands and thus reduces the effect of GVD. Compression of the chirped beatnotes can be implemented in a separate plasma of higher density, where the laser sidebands become uncoupled.
Characterization Of A Clustering Gas Jet For High Energy Density Plasma Production
(2019-05-01) Glenn, Griffin Dale; Ditmire, Todd
When expanding through a nozzle into a vacuum in a high-pressure-backed supersonic jet, certain gases can condense into van der Waals-bound atomic or molecular clusters. These clusters absorb intense, pulsed laser light more efficiently than uniform gas jets of the same average density, making them useful sources of high energy density plasmas. An argon gas jet designed to produce such clusters was studied using Rayleigh scattering and interferometry.
Characterization of a Clustering Gas Jet for High Energy Density Plasma Production
(2019-05-21) Glenn, Griffin Dale; Ditmire, Todd
When expanding through a nozzle into a vacuum in a high-pressure-backed supersonic jet, certain gases can condense into van der Waals-bound atomic or molecular clusters. These clusters absorb intense, pulsed laser light more efficiently than uniform gas jets of the same average density, making them useful sources of high energy density plasmas. An argon gas jet designed to produce such clusters was studied using Rayleigh scattering and interferometry.
Coherently Controlled Quantum Emitters In Cavities
(2010-02) Muller, A.; Flagg, E. B.; Deppe, D. G.; Salamo, G. J.; Shih, C. K.; Muller, A.; Flagg, E. B.; Shih, C. K.
Semiconductor nanostructures such as quantum dots (QDs) have offered unique opportunities to investigate quantum optical effects in solid-state systems. These include quantum interference, Rabi oscillations, as well as photon antibunching, and were previously observable only in isolated atoms or ions. In addition, QDs can be integrated into optical microcavities, making them attractive for applications in quantum information processing and high efficiency quantum light sources. Despite much progress towards these goals, one area that was little explored is coherent control of such solid-state quantum emitters in cavities. The main technical hurdle lies in overcoming the laser background scattering. By using a sample structure in which QDs are embedded in a planar Fabry-Perot cavity and by using an orthogonal excitation geometry, we have achieved a nearly complete elimination of laser background scattering. This in turn allows us to show resonantly controlled light emission of quantum dots in the cavity including (a) Rabi flopping using pulse control, (b) direct observation of Mollow triplets in the frequency domain, and (c) simultaneously measured first-order and second order photon-photon correlations.
Design And Fabrication Of A Surface-Wave Accelerator Based On Silicon Carbide
(2004-12) Shvets, G.; Kalmykov, S.; Shvets, Gennady; Kalmykov, Sergey
The principles and electromagnetic simulations of a novel accelerating structure are described. The structure is planar, consisting of two plates of silicon carbide (SiC) separated by a vacuum gap. Charged particle bunches are accelerated in the vacuum gap by the surface electromagnetic waves (phonon polaritons) localized near the vacuum/SiC interface. The structure can be powered by a carbon dioxide (CO2) laser with the wavelength lambda(0) approximate to 10.6mum. The operating wavelength is dictated by the frequency-dependent dielectric permittivity epsilon(omega) of SiC which is negative for the frequencies in the CO2 tunability range. The resulting accelerator can support accelerating fields well in excess of 1 GeV/m without breakdown, and provide the path to compact and inexpensive particle accelerators. The challenge of coupling radiation into a very narrow (a few microns) vacuum gap is resolved by designing a coupling grating on the top surface of a Si wafer, and attaching a thin SiC film to the bottom of the wafer. Preliminary fabrication results are reported.
Development Of 873 nm Raman Seed Pulse For Raman-Seeded Laser Wakefield Acceleration
(2004-12) Grigsby, F.; Peng, D.; Downer, M. C.; Grigsby, F.; Peng, D.; Downer, M. C.
By using a Raman-shifted seed pulse coincident with a main driving pulse. laser wakefields can be generated with sub-relativistic intensity, coherent control and high repetition rate in the self-modulated regime. Experimentally, the generation of a chirped Stokes laser pulse by inserting a solid state Raman shifter, Ba(NO3)(2), into a CPA system before the compressor (to suppress self-phase modulation) will be described. We will also report on design. modeling and experimental demonstration of a novel compressor for the Stokes pulse that uses a mismatched grating pair to achieve a near transform-limited seed pulse. Finally, we will describe the design. simulation and current status of Raman-seeded LWFA experiments that use this novel source..
Femtosecond Pump-Probe Diagnostics Of Preformed Plasma Channels
(2004-12) Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.; Zgadzaj, R.; Gaul, E. W.; Matlis, N. H.; Shvets, G.; Debus, A.; Downer, M. C.
We report on recent ultrafast pump-probe experiments 28 in He plasma waveguides using 800 nm, 80 fs pump pulses of 0.2 x 1018 W/cm2 peak guided intensity, and single orthogonally-polarized 800 nm probe pulses with similar to0.1% of pump intensity. The main results are: (1) We observe frequency-domain interference between the probe and a weak, depolarized component of the pump that differs substantially in mode shape from the injected pump pulse; (2) we observe spectral blue-shifts in the transmitted probe that are not evident in the transmitted pump. The evidence indicates that pump depolarization and probe blue-shifts both originate near the channel entrance.
Fundamental Study Of Optical Threshold Layer Approach Towards Double Exposure Lithography
(2009-04) Gu, X. Y.; Berro, A. J.; Cho, Y.; Jen, K.; Lee, S.; Nagai, T.; Ogata, T.; Durand, W. J.; Sundaresan, A.; Lancaster, J. R.; Jockusch, S.; Zimmerman, P.; Turro, N. J.; Willson, C. G.; Gu, Xinyu; Cho, Younjin; Jen, Kane; Lee, Saul; Ngai, Tomoki; Durand, William J.; Jockusch, Steffen; Willson, C. G.
193 immersion lithography has reached its maximal achievable resolution. There are mainly two lithographic strategies that will enable continued increase in resolution. Those are being pursued in parallel. The first is extreme ultraviolet (EUV) lithography and the second is double patterning (exposure) lithography. EUV lithography is counted on to be available in 2013 time frame for 22 nm node([1]). Unfortunately, this technology has suffered several delays due to fundamental problems with source power, mask infrastructure, metrology and overall reliability([2]). The implementation of EUV lithography in the next five years is unlikely due to economic factors. Double patterning lithography (DPL) is a technology that has been implemented by the industry and has already shown the proof of concept for the 22nm node([3]). This technique while expensive is the only current path forward for scaling with no fundamental showstoppers for the 32nm and 22nm nodes. Double exposure lithography (DEL) is being proposed as a cost mitigating approach to advanced lithography. Compared to DPL, DEL offers advantages in overlay and process time, thus reducing the cost-of-ownership (CoO)([4][5]). However, DEL requires new materials that have a non-linear photoresponse. So far, several approaches were proposed for double exposure lithography, from which Optical Threshold Layer (OTL) was found to give the best lithography performance according to the results of the simulation([4][5]). This paper details the principle of the OTL approach. A photochromic polymer was designed and synthesized. The feasibility of the material for application of DEL was explored by a series of evaluations.
LWFA With Low Energy Raman Seeded Pulses
(2004-12) Fomyts'kyi, M.; Chiu, C.; Downer, M.; Grigsby, F.; Fomyts’kyi, Mykhailo; Chiu, Charles; Downer, Michael; Grigsby, Franklin
Analytical and numerical calculations of plasma wakefield excitation and particle acceleration by Raman seeded laser pulse in self-modulation regime are presented. We derive energy threshold for self-modulation of diffraction-limited pulses. The parameter range where the Raman seeded amplitude plays an important role is investigated. We show that the seeded amplitude provides a coherent control mechanism for the phase of the wakefield wave. We show that with the use of Raman seed self-modulated wakefield acceleration is achievable for the pulses of intensities much lower than those typically used in the experiments. In particular, our 2D particle-in-cell simulations show that 30 mJ pulse combined with Raman seeded pulse, which is 1% in intensity of the main pulse is capable of generating similar to1 nC of relativistic electrons.
Metamaterial Structural Design: Creating optical-frequency metamaterials with plasmonic nano-particle arrangements and generating unit cells with evolutionary algorithms
(2011) Esteva, Carlos Andres; Alu, Andrea
Metamaterials are artificial structures which can manipulate electromagnetic (EM) waves at will. These periodic lattices give engineers and researchers a large degree of control over EM radiation and can be used to create exciting and novel applications such as invisibility cloaks, superlenses, and devices with negative indices of refraction. The geometrical design of these structures is a large challenge in creating them. These structures are periodic lattices with magnetodielectric, metallic, or plasmonic inclusions. Their size, which scales on the order of the wavelength of interest, and their geometry uniquely determine the effect on EM waves as well as the frequency bands in which they operate. We present in this thesis the development of a bi-directional computational platform for metamaterial structural design. This platform serves to extract, from a given geometry, the bulk material properties of the corresponding metamaterial. It further serves to generate metamaterial unit cells which satisfy pre-determined sets of material parameters. This work is split between The University of Texas at Austin and Sandia National Laboratories
Methods of Depositing Anti-Reflective Coatings for Additively Manufactured Optics
(University of Texas at Austin, 2018) Beller, Z.J.; Secor, E.B.; Lavin, J.; Keicher, D.M.; Essien, M.; Whetten, S.; Mani, S.S.
Recent advancements in the field of additive manufacturing (AM) have enabled the production of high-fidelity optical components allowing for the design of novel fiber optic systems. In order to support this emerging technology, methods of depositing anti-reflective coatings (ARCs) onto these optical components must be developed. Work has begun to identify such coating materials; develop systems capable of accurately depositing controlled, uniform layers onto given substrates; establish deposition procedures for ensuring coating validity; and establish post-processing procedures to ensure the reliability of finished components. Areas of interest for finished components include their integration into high-bandwidth fiber optic systems, enabling further miniaturization of communication components. Methods of ARC deposition will be discussed along with final component performance and the identification of key process parameters affecting product performance.
One Photon at a Time
(The Texas Scientist, 2020) The Texas Scientist
Optical Threshold Layer And Intermediate State Two-Photon Pag Approaches To Double Exposure Lithography
(2009-04) Berro, A. J.; Gu, X. Y.; O'Connor, N.; Jockusch, S.; Nagai, T.; Ogata, T.; Zimmerman, P.; Rice, B. J.; Adolph, E.; Byargeon, T.; Gonzalez, J.; Turro, N. J.; Willson, C. G.; Berro, Adam J.; Gu, Xinyu; Nagai, Tomoki; Ogata, Toshiyuki; Adolph, Elizabeth; Byargeon, Travis; Gonzalez, Jose; Willson, C. Grant
Intermediate state two-photon (ISTP) photoacid generator (PAG) and optical threshold layer (OTL) approaches to double exposure lithography have been explored. We have synthesized >transparent> PAG and sensitizer compounds for use in ISTP systems and have demonstrated the possibility of utilizing such energy transfer systems to generate acid. We have also synthesized side chain liquid crystalline polymers and small molecule azobenzene compounds for use in OTL applications and have begun photoswitching studies.
Optimized Retinal Nerve Fiber Layer Segmentation Based On Optical Reflectivity And Birefringence For Polarization-Sensitive Optical Coherence Tomography
(2011-09) Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. Grady; Wang, Bingqing; Paranjape, Amit S.; Yin, Biwei; Liu, Shuang; Markey, Markey K.; Milner, Thomas E.; Rylander, H. Grady
Segmentation of the retinal nerve fiber layer (RNFL) from swept source polarization-sensitive optical coherence tomography (SS-PSOCT) images is required to determine RNFL thickness and calculate birefringence. Traditional RNFL segmentation methods based on image processing and boundary detection algorithms utilize only optical reflectivity contrast information, which is strongly affected by speckle noise. We present a novel approach to segment the retinal nerve fiber layer (RNFL) using SS-PSOCT images including both optical reflectivity and phase retardation information. The RNFL anterior boundary is detected based on optical reflectivity change due to refractive index difference between the vitreous and inner limiting membrane. The posterior boundary of the RNFL is a transition zone composed of birefringent axons extending from retinal ganglion cells and may be detected by a change in birefringence. A posterior boundary detection method is presented that segments the RNFL by minimizing the uncertainty of RNFL birefringence determined by a Levenberg-Marquardt nonlinear fitting algorithm. Clinical results from a healthy volunteer show that the proposed segmentation method estimates RNFL birefringence and phase retardation with lower uncertainty and higher continuity than traditional intensity-based approaches.
Particle Generation During Photoresist Dissolution
(2010) Chauhan, S.; Somervell, M.; Carcasi, M.; Scheer, S.; Bonnecaze, R. T.; Mack, C.; Willson, C. G.; Chauhan, Siddharth; Bonnecaze, Roger T.; Willson, C. Grant
A lattice-type Monte Carlo based mesoscale model and simulation of the lithography process has been described previously [1]. The model includes the spin coating, post apply bake, exposure, post exposure bake and development steps. This simulation has been adapted to study the insoluble particle generation that arises from statistically improbable events. These events occur when there is a connected pathway of soluble material that envelops a volume of insoluble material due to fluctuations in the deprotection profile that occur during the post exposure bake [2]. Development erodes the insoluble material into the developer stream as an insoluble particle. This process may produce a cavity on the line edge that can be far larger than a single polymer molecule. The insoluble particles generated may coalesce in developer to form large aggregates of insoluble material that ultimately deposit on the wafer surface and the tooling. The recent modifications made in mesoscale models for the PEB and dissolution steps, which have enabled this study are briefly described. An algorithm that was used for particle detection in the current study is also discussed. The effect of the resist formulation and the different lithographic steps, namely, exposure, post exposure bake and development, on the extent of particle generation is analyzed. These simulations can be used to set process variables to minimize the extent of particle generation.
Photobase Generator Assisted Pitch Division
(2010-02) Gu, X. Y.; Bates, C. M.; Cho, Y. J.; Kawakami, T.; Nagai, T.; Ogata, T.; Sundaresan, A. K.; Turro, N. J.; Bristol, R.; Zimmerman, P.; Willson, C. G.; Gu, Xinyu; Kawakami, Takanori; Nagai, Tomoki; Willson, C. Grant
The drive to sustain the improvements in productivity that derive from following Moore's law has led the semiconductor industry to explore new technologies that enable production of smaller and smaller features on semiconductor device. Pitch division techniques and double exposure lithography are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by modifying the lithographic process. This paper presents a new technique that enables pitch division in the printing of gratings using only a single exposure that is fully compatible with the current manufacturing tools. This technique employs a classical photoresist polymer together with a photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator (PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the low dose regions. This photoactive system can be exploited in the design of both positive tone and negative tone resist formulations that provide a developed image of a grating that is twice the frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half pitch relief image after development. Through this new technique, a 45 nm half pitch line and space pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This corresponds to a k(1) factor of 0.13. The principles, the materials design and the first lithographic evaluations of this system are reported.
Photobase Generator Enabled Pitch Division: A Progress Report
(2011-04) Gu, X. Y.; Cho, Y. J.; Kawakami, T.; Hagiwara, Y.; Rawlings, B.; Mesch, R.; Ogata, T.; Kim, T.; Seshimo, T.; Wang, W. D.; Sundaresan, A. K.; Turro, N. J.; Gronheid, R.; Blackwell, J.; Bristol, R.; Willson, C. G.; Cho, Younjin; Hagiwara, Yuji; Mesch, Ryan; Ogata, Toshiyuki; Kim, Taeho; Seshimo, Takehiro; Wang, Wade; Willson, C. Grant
Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice the pitch of a mask. The proof-of-concept has been published in the previous paper[1, 2] and demonstrated by others[1]. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the LER in this process. Challenges were summarized toward low LER and good performing pitch division. Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.
Planarizing Material For Reverse-Tone Step And Flash Imprint Lithography
(2010) Ogawa, Tsuyoshi; Takei, Satoshi; Jacobsson, B. Michael; Deschner, Ryan; Bell, William; Lin, Michael W.; Hagiwara, Yuji; Hanabata, Makoto; Willson, C. Grant; Ogawa, Tsuyoshi; Jacobsson, B. Michael; Deschner, Ryan; Bell, William; Lin, Michael W.; Hagiwara, Yuji; Willson, C. Grant
Reverse-tone Step and Flash Imprint Lithography (S-FIL/R) requires materials that can be spin coated onto patterned substrates with significant topography and that are highly-planarizing. Ideally, these planarizing materials must contain silicon for etch selectivity, be UV or thermally curable, have low viscosity, and low volatility. One such novel material in particular, a branched and functionalized siloxane (Si-12), is able to adequately satisfy the above requirements. This paper describes a study of the properties of epoxy functionalized Si-12 (epoxy-Si-12) as a planarizing layer. An efficient synthetic route to epoxy-Si-12 was successfully developed, which is suitable and scalable for an industrial process. Epoxy-Si-12 has a high silicon content (30.0 %), low viscosity (29 cP @ 25 degrees C), and low vapor pressure (0.65 Torr @ 25 degrees C). A planarizing study was carried out using epoxy-Si-12 on trench patterned test substrates. The material showed excellent planarizing properties and met the calculated critical degree of planarization (critical DOP), which is a requirement for a successful etch process. An S-FIL/R process using epoxy-Si-12 was demonstrated using, an Imprio (R) 100 (Molecular Imprints Inc., USA) imprint tool. The results indicate that epoxy-Si-12 works very well as a planarizing layer for S-FIL/R.
Polymer Bound Photobase Generators And Photoacid Generators For Pitch Division Lithography
(2011-04) Cho, Y. J.; Gu, X. Y.; Hagiwara, Y.; Kawakami, T.; Ogata, T.; Rawlings, B.; Li, Y. J.; Sundaresan, A. K.; Turro, N. J.; Bristol, R.; Blackwell, J. M.; Willson, C. G.; Cho, Younjin; Gu, Xinyu; Hagiwara, Yuji; Kawakami, Takanori; Rawlings, Brandon; Willson, C. Grant
The semiconductor industry is pursuing several process options that provide pathways to printing images smaller than the theoretical resolution limit of 193 nm projection scanners. These processes include double patterning, side wall deposition and pitch division. Pitch doubling lithography (PDL), the achievement of pitch division by addition of a photobase generator (PBG) to typical 193 nm resist formulations was recently presented. 1 Controlling the net acid concentration as a function of dose by incorporating both a photoacid generator (PAG) and a PBG in the resist formulation imparts a resist dissolution rate response modulation at twice the frequency of the aerial image. Simulation and patterning of 45 nm half pitch L/S patterns produced using a 90 nm half pitch mask were reported. 2 Pitch division was achieved, but the line edge roughness of the resulting images did not meet the current standard. To reduce line edge roughness, polymer bound PBGs and polymer bound PAGs were investigated in the PDL resist formulations. The synthesis, purification, analysis, and functional performance of various polymers containing PBG or PAG monomers are described herein. Both polymer bound PBG with monomeric PAG and polymer bound PAG with monomeric PBG showed a PDL response. The performance of the polymer bound formulations is compared to the same formulations with small molecule analogs of PAG and PBG.
Polymer Dissolution Model: An Energy Adaptation Of The Critical Ionization Theory
(2009-02) Chauhan, S.; Somervell, M.; Scheer, S.; Mack, C.; Bonnecaze, R. T.; Willson, C. G.; Chauhana, Siddharth; Bonnecaze, Roger T.; Willson, C. Grant
The current scale of features size in the microelectronics industry has reached the point where molecular level interactions affect process fidelity and produce excursions from the continuum world like line edge roughness (LER). Here we present a 3D molecular level model based on the adaptation of the critical ionization (CI) theory using a fundamental interaction energy approach. The model asserts that it is the favorable interaction between the ionized part of the polymer and the developer solution which renders the polymer soluble. Dynamic Monte Carlo methods were used in the current model to study the polymer dissolution phenomenon. The surface ionization was captured by employing an electric double layer at the interface, and polymer motion was simulated using the Metropolis algorithm. The approximated interaction parameters, for different species in the system, were obtained experimentally and used to calibrate the simulated dissolution rate response to polymer molecular weight and developer concentration. The predicted response is in good agreement with experimental dissolution rate data. The simulation results support the premise of the CI theory and provide an insight into the CI model from a new prospective. This model may provide a means to study the contribution of development to LER and other related defects based on molecular level interactions between distinct components in the polymer and the developer.