bluuebunny/crossref_metadata_2025 huggingface dataset:
Lidar In-space Technology Experiment - Overview and Early Results
Authors: McCormick M. Patrick
Published: February 2023

The September 1994 Shuttle flight of the Lidar In-space Technology Experiment (LITE) brought to fruition 10 years of effort at NASA's Langley Research Center where it was built. Being the first flight of a spaceborne lidar to measure atmospheric constituents and parameters and surface properties, it culminates the efforts of many worldwide over the last 20 years to usher in this new remote sensing technique from space.
New Generation Lidar Systems for Eye Safe Full Time Observations
Authors: Spinhirne James D.
Published: February 2023

The traditional lidar over the last thirty years has typically been a big pulse low repetition rate system. Pulse energies are in the 0.1 to 1.0 J range and repetition rates from 0.1 to 10 Hz. While such systems have proven to be good research tools, they have a number of limitations that prevent them from moving beyond lidar research to operational, application oriented instruments. These problems include a lack of eye safety, very low efficiency, poor reliability, lack of ruggedness and high development and operating costs.
High resolution Interferometer Sounder - An Accurate Method for Profile Retrieval Without the Use of Contemporary "First Guess" Data
Authors: Smith W.L. , Huang H.L. , Ma X.L. , Woolf H. M. , Revercomb H.E.
Published: February 2023

The High resolution Interferometer Sounder (HIS), is a Michelson interferometer which observes the spectrum of infrared radiance (3.5 - 18 μm) with a spectral resolution ( λ/Δλ) better than 2000/1. During 1994, the HIS flew aboard the NASA ER-2 during a series of flights between Christchurch New Zealand and the Antarctic ice shelf as part of the Airborne Southern Hemisphere Ozone Experiment (ASHOE). The intent of the HIS was to retrieve atmospheric profiles of temperature, water vapor, and ozone beneath the Aircraft (20 Km) flight level. The profile retrievals are needed to validate global Numerical Weather Prediction (NWP) models used to prescribe the thermodynamic and dynamic variables used to estimate the chemical interactions and transports of the molecules responsible for Ozone depletion (i.e., the "Ozone Hole"). In order to accomplish this objective, a procedure for profile retrieval had to be developed which was both accurate and independent of the contemporary meteorological observations which influence NWP models; needless to say a model forecast could not be used as an initial guess for the retrieval process. Because of the extensive cloudiness over the Southern Oceans, the method had to be able to provide accurate retrievals above clouds, regardless of their altitude or their opacity. This paper describes the method developed for this application and provides results from the spectral radiance data obtained during the ASHOE to demonstrate their accuracy.
Alexandrite Laser Transmitter Development for Airborne Water Vapor DIAL Measurements
Authors: Chyba Thomas H. , Ponsardin Patrick , Higdon Noah S. , DeYoung Russell J. , Browell Edward V.
Published: February 2023

In the DIAL technique, the water vapor concentration profile is determined by analyzing the lidar backscatter signals for laser wavelengths tuned "on" and "off a water vapor absorption line. Desired characteristics of the on-line transmitted laser beam include: pulse energy ≥100 mJ, high-resolution tuning capability (uncertainty < 0.25 pm), good spectral stability (jitter <0.5 pm about the mean), and high spectral purity (>99%).1 The off-line laser is generally detuned less than 100 pm away from the water vapor line. Its spectral requirements are much less stringent.
Remote Sensing Measurements of Atmospheric Methane at 2.3 microns with a Nonmechanical GFCR
Authors: Wang Liang-guo , Sachse Glen , Wallio Andrew , LeBel Peter , Vay Stephanie
Published: February 2023

Gas filter correlation radiometer (GFCR) is a passive remote sensing technique used in a variety of atmospheric measurements.1 In recent years, a nonmechanical optical switching GFCR has been invented and developed at NASA Langley Research Center. The principle of the new GFCR and some preliminary lab experimental results were reported in earlier papers.2,3 The use of a polarization modulator, in conjunction with a polarization beamsplitter, enables rapid optical switching without mechanically moving parts. In comparison with the conventional GFCR, which involves mechanical chopping or switching between two optical paths, the nonmechanical GFCR possesses some very attractive advantages such as fast sampling rate, high reliability, low weight and long operational life time.
Absolute Frequency Wind Measurements for Doppler-Rayleigh Lidar
Authors: Friedman J.S. , Castleberg P.A. , Cho J.Y.N. , Tepley C.A. , Kelley M.C.
Published: February 2023

The Doppler-Rayleigh lidar at Arecibo Observatory has been in operation since May 1990 obtaining wind data in the region of the atmosphere between 10 and 60 km altitude where it is difficult to measure atmospheric properties by balloons, satellites, or radars. An injection-seeded Nd:YAG laser coupled with a Fabry-Perot etalon receiver are capable of giving a frequency resolution of about 20 MHz. The etalon is pressure tuned in discrete steps about the center frequency of the transmitter. To get the horizontal component of the wind vector, the laser is pointed 30° off the zenith to the north or south and to the east or west. A zero wind marker for reference is obtained by pointing the lidar vertically. It is assumed that vertical winds are substantially smaller than horizontal and not measurable by the lidar. Long term drifts in the center frequency caused by both drift in the seed laser and in the etalon receiver are compensated for by taking out the drift of the fringes measured in the vertical direction. This uncertainty in frequency drift of the system and the need to depend on the assumption of zero vertical wind velocities are weaknesses in the measurements, and they render the uncertainty of Doppler shift measurements to be much greater than 20 MHz.
Line-center/Side-line Diode Laser Seeding for DIAL Measurements of the Atmosphere
Authors: Sachse Glen , Wang Liang-guo , Antill Charles , Ismail Syed , Browell Edward
Published: February 2023

The ability of DIAL systems to probe deeply into the atmosphere is enhanced if the pulsed laser is capable of sequentially operating at different wavelengths, each wavelength corresponding to a different absorption cross-section of the gas of interest. Such wavelength versatility is particularly important for airborne or spacebome DIAL measurements of H2O(v) due to its strong vertical gradient (several orders of magnitude). Strong H2O(v) cross-sections are necessary to retrieve H2O(v) data from high altitudes while the use of weaker cross sections enables penetration of the DIAL laser pulses to lower altitudes.
Contrail Observation by Ground-Based Scanning Lidar: Spatial Growth
Authors: Freudenthaler Volker , Homburg Frank , Jäger Horst
Published: February 2023

The analysis of satellite data reveals an additional cloud cover due to contrails of 0.4% over mid-Europe (Schumann and Wendling, 1990) and up to 2% over the eastern part of the Atlantic Ocean ( Bakan et.al., 1994). The contrails consist of ice crystals and form from the additional water vapour emitted by high flying aircrafts. Their persistence (up to some hours) depends on the ambient temperature and humidity (Appelman, 1953, Boin and Levkov, 1994). To evaluate the impact of contrails on the earth's radiation budget, their extension and optical parameters must be known. This paper describes a scanning lidar system dedicated to the measurement of contrails, and an analysis of the temporal and spatial evolution of seven contrails.
Water Vapor Spectroscopy in the 815-nm Wavelength Region for Differential Absorption Lidar Measurements
Authors: Ponsardin Patrick , Browell Edward V.
Published: February 2023

The differential absorption lidar (DIAL) technique was first applied to the remote measurement of atmospheric water vapor profiles from airborne platforms in 1981 [1]. The successful interpretation of the lidar profiles relies strongly on an accurate knowledge of specific water vapor absorption line parameters: line strength, pressure broadening coefficient, pressure-induced shift coefficient and the respective temperature-dependence factors [2]. NASA Langley Research Center has developed and is currently testing an autonomous airborne water vapor lidar system: LASE (Lidar Atmospheric Sensing Experiment). This DIAL system uses a Nd:YAG-pumped Ti:Sapphire laser seeded by a diode laser as a lidar transmitter. The tunable diode has been selected to operate in the 813-818 nm wavelength region. This 5-nm spectral interval offers a large distribution of strengths for temperature-insensitive water vapor absorption lines. In support of the LASE project, a series of spectroscopic measurements were conducted for the 16 absorption lines that have been identified for use in the LASE measurements. Prior to this work, the experimental data for this water vapor absorption band were limited - to our knowledge - to the line strengths and to the line positions [3].
The New Design of the IFU Tropospheric Ozone Lidar
Authors: Eisele H. , Trickl T.
Published: February 2023

In 1990, a UV lidar for measurements of the vertical distribution of tropospheric ozone was completed at IFU. The wide range of this system (0.1 to 10 km) has made possible investigations of ozone in all layers of the troposphere. In 1991, the operation of the lidar started. Almost 580 sets of backscatter profiles were recorded during that year and the diurnal and annual ozone variations in the different seasons could be traced.
Recent Developments and Field Tests of the NASA Langley Research Center Airborne Water Vapor DIAL System
Authors: Higdon Noah S. , Chyba Thomas H. , Ponsardin Patrick , De Young Russell J. , Browell Edward V.
Published: February 2023

An airborne differential absorption lidar (DIAL) system has been developed at the NASA Langley Research Center for the remote measurement of water vapor (H2O) and aerosols in the lower troposphere. Significant modifications to the laser transmitters and other major subsystems have been implemented during the past two years to improve the system's performance and field reliability. The previous configuration of the airborne H2O DIAL system and the associated atmospheric data collected during flight tests at Wallops Flight Facility are described in detail in two recently published papers (Higdon et al., 1994 and Ponsardin et al., 1994). The modified system is to be flight tested in late 1994, and the system performance characteristics and preliminary atmospheric H2O and aerosol data from these flights are discussed in this paper.
An Interleave Retrieval Method for Oversampled Limb Scans
Authors: Gordley Larry L. , Marshall Benjamin T. , Deaver Lance E.
Published: February 2023

Rodgers1 presents a general approach for error analysis of retrievals based on a linearization of the retrieval problem. This approach allows calculation of retrieval error from uncertainties in the input radiances and in each of the forward radiance model parameters. These terms are weighted according to the sensitivity of the retrieval to each of them. We use this framework to describe the results of an error analysis performed on HALOE2 data. This paper will show the effect of using oversampled profile data and an interleave retrieval technique by application of formal error analysis.
An Algorithm to Derive Aerosol Properties From Multi-Wavelength/Angle Radiance Measurements
Authors: Porter John N. , Clarke Antony D. , Rolland Phillipe
Published: February 2023

A knowledge of aerosol optical properties and concentrations is required for modeling their impact on radiative transfer. These aerosol properties are often derived from passive radiation measurements at several wavelengths. In doing this, one encounters the problem that the multi-wavelength information is not sufficient to address the various unknown aerosol properties including concentration, aerosol size distribution, phase function, single scatter albedo and index of refraction. In order to address this problem, a new aerosol model was developed from in-situ aerosol measurements which were carried out in the Pacific, Atlantic and Indian Ocean. After sorting each aerosol distribution by their dry mass they were combined and a double lognormal curve was used to fit the resulting distributions. A example of the model sulfate accumulation mode and sea salt coarse mode is shown in figures 1 and 2.
Lidar Measurements at Lauder, NZ
Authors: McGee Thomas J. , Gross Michael , Singh Upendra , Kimvilakani Patrick
Published: February 2023

In March of 1994, the GSFC Stratospheric Ozone Lidar was deployed to the Network for the Detection of Stratospheric Change (NDSC) site at Lauder, NZ. This was in conjunction with a series of NASA ER-2 flights from Christchurch, NZ south to the Antarctic Circle. These flights were organized to study the chemistry of the stratosphere before, during and after the formation of the well-known "ozone hole". Lidar measurements were made at four different time periods corresponding to the times of the ER-2 flights. Lauder is situated nearly along the flight path as the aircraft flew south and so the lidar measurements provide a checkpoint for the ozone, aerosol and temperature instruments on board the aircraft. Whenever the weather permitted, lidar measurements were made as near to dawn, prior to the flight, and as near to sunset, after the flight. This provided data as close to the aircraft transit time as possible.
Ozone vertical distribution retrieval from ground-based high resolution infrared solar spectra
Authors: Pougatchev N. S. , Connor B. J. , Rinsland C. P.
Published: February 2023

A practical procedure for the retrieval of ozone vertical profiles from ground-based high resolution Fourier transform infrared solar spectra has been developed. The analysis is based on a multilayer line-by-line forward model and a semi-empirical version of the optimal estimation inversion method of Rodgers [1]. The 1002.6-1003.2 cm-1 spectral interval has been selected for the analysis on the basis of synthetic spectrum calculations (see Fig. 1). This interval contains numerous ozone lines covering a range of intensities and providing retrieval sensitivity from ground level to about 35 km. Characterization of the method and an error analysis have been performed. For a spectral resolution of 0.05–0.01 cm-1 and a signal-to-noise ratio ≥100 the retrieval is stable with a vertical resolution of ≈5 km attainable near the surface degrading to ≈10 km in the stratosphere. Synthetic spectra studies show that the a priori profile and weak constraints selected for the retrievals introduce no significant biases for a wide range of ozone profiles.
Total Column Ozone Retrieval from the Visible Chappuis Band: Comparisons with Standard Ultraviolet Measurements
Authors: Michalsky Joseph , Harrison Halstead
Published: February 2023

Standard measurements of total column ozone are made in the ultraviolet portion of the spectrum in the Huggins bands, using wavelengths between 305 and 340 nm. Dobson spectrophotometers (Dobson 1931), Brewer spectrophotometers (Wardle et al. 1963), and M-83 filter ozonometers (Gushchin et al. 1985) are standard ground-based instruments for these ultraviolet total column ozone measurements. They each use wavelength pairs to get a differential absorption between strong and relatively weaker portions of the ozone spectrum.
Fourier transform infrared sounding for the NDSC
Authors: Mankin William G.
Published: February 2023

Global, high quality measurements of the composition and physical conditions of the stratosphere are necessary for progress in the studies of changes in the ozone layer. To this end, the Network for Detection of Stratospheric Change (NDSC) has been established, based on the premise that a better global picture can be obtained by combining data from satellites, which have wide geographic coverage, with data from a few groundbased stations, where the instruments can be carefully characterized and calibrated repeatedly and a wide variety of instruments can be used simultaneously, than can be obtained with either type of data alone. The NDSC consists of a set of high quality remote sounding research stations for observing and understanding the physical and chemical state of the stratosphere1. The stations include both primary and complementary observing sites. The data from these stations are complemented with satellite measurements. The observations are targeted primarily at ozone and related chemical compounds and parameters.
Intercomparison of Lidar-Derived Temperatures during the MLO3 NDSC Validation at Mauna Loa, HI, August, 1995
Authors: McGee T. J. , Gross M. R. , Singh U. , McDermid I. S. , Barnes J. , Hofmann D.
Published: February 2023

During August of 1995, a number of scientific groups gathered at Mauna Loa Observatory, on the island of Hawaii, to participate in an ozone lidar instrument validation campaign. The two ozone lidars which participated, also are capable of retrieving upper atmosphere temperature profiles from the data collected and so it was decided to use this opportunity to compare the temperature capabilities of the instruments. NOAA has for many years operated a Rayleigh lidar at the site. This had just recently been upgraded to a Nd-YAG lidar. The Goddard Space Flight Center also shipped a new Temperature and Aerosol Lidar to the site for this campaign.
Determination of Column Water Vapour Content of the Atmosphere by using the backscattered Solar Radiation at the Top of the Atmosphere
Authors: Tahl Sigrun , Schönermark Maria v.
Published: February 2023

The Modular Optoelectronical Scanner (MOS) is working on the Indian Remote Sensing Satellite (IRS) as well as on the PRIRODA module of the Russian Space Station MIR. MOS had been built by the Institute of Space Sensor Technology of the German Aerospace Research Establishment (DLR) and was mainly developed for determining the colour and the substances of the ocean and the coastal waters. The sensor launched with the IRS consists of three units: the main sensor, which is the imaging biospectrometer MOS-B equipped with 13 channels between 408 nm and 1010 nm with a bandwidth of approximately 10 nm, the imaging atmosphere-spectrometer MOS-A provided with four small channels within the oxygen-A-band at 760 nm and a MOS-C-Camera working at 1.6 μm. A technical description of the MOS is given by Neumann (1995).
Remote Sensing of Tropospheric Ozone and its Precursors
Authors: Beer Reinhard
Published: February 2023

Two closely-related imaging infrared Fourier Transform Spectrometers - the Tropospheric Emission Spectrometer (TES; scheduled for launch on the Earth Observing System CHEM-I platform in 2001) and the Airborne Emission Spectrometer (AES; completed in 1994 and flown on a variety of NASA aircraft) - are aimed at elucidating the chemistry of the troposphere on global and regional scales with far better coverage (spatial and temporal) than is feasible with in situ sensors during intermittent field and aircraft campaigns.
Atmospheric Lidar as a Commercial Venture
Authors: Ulitsky Arkady , Carswell Allan
Published: February 2023

Many atmospheric lidars have been constructed but there is little progress in commercial product development. Some of the factors involved are discussed based on Optech’s experience.
Tropospheric Wind Measurements with an Airborne Scanning Coherent Doppler Lidar
Authors: Rothermel Jeffry , Hardesty R. Michael , Howell James N. , Johnson Steven C. , Menzies Robert T. , Tratt David M. , Cutten Dean R.
Published: February 2023

Since the first remote wind measurements in 1967, coherent Doppler lidar has become established as a unique tool for atmospheric research. Remote sensing of the two-dimensional horizontal wind field with airborne coherent Doppler lidar was demonstrated in 1981 using a low-energy scanning CO2 lidar.1 The scanner and operations control system were subsequently improved to enable wind field measurements at multiple vertical levels, and the system was reflown in 1984.2 Subsequent advances in coherent CO2 laser technology resulted in the development of a frequency-stable, high energy-per-pulse transmitter (~1 J) which was delivered to the National Oceanic and Atmospheric Administration (NOAA) and incorporated into an existing portable ground-based lidar system.3 Thus the possibility arose for the cooperative development of an airborne system with dramatically improved performance, hence greater scientific applications, owing to lower backscatter sensitivity and broader spatial coverage. In 1992 the lidar atmospheric remote sensing groups of the National Aeronautics and Space Administration (NASA) Marshall Space Flight Center (MSFC), NOAA Environmental Technology Laboratory (ETL), and Jet Propulsion Laboratory (JPL) jointly developed MACAWS, the Multicenter Airborne Coherent Atmospheric Wind Sensor. Existing components were used when possible to minimize programmatic costs. The high-energy laser transmitter is borrowed from the NOAA windvan lidar.3 The ruggedized optical table assembly is borrowed in part from an airborne backscatter lidar developed and flown by JPL. The scanner, telescope and other components are borrowed from a previous airborne Doppler lidar system which was limited in performance primarily to high-backscatter boundary layer features.1,2 Some hardware modifications were required to ensure flight safety, reliability, and compatibility with the aircraft environment.
Regional ozone mapping with the Airborne Emission Spectrometer (AES) for flights during the July, 1995 Southern Oxidants Study in Nashville, TN
Authors: Worden H. , Nandi S. , Rider D. , Beer R.
Published: February 2023

We present our retrievals of urban and rural ozone abundance, temperature and humidity for data taken with the 0.07 cm-1 resolution, 3.3 to 14 micron AES Fourier transform spectrometer.
Passive Remote Sensing of Elements of the Aerosol Scattering Matrix: Simulations
Authors: Zhang Tianming , Gordon Howard R.
Published: February 2023

Based on an algorithm presented by Wang and Gordon 1 for estimating the aerosol scattering phase function P11(Θ) and single scattering albedo ω0 from measurements of sky radiance and aerosol optical thickness over the oceans, we formulated and tested2,3 an extension that utilizes the radiance reflected from the ocean atmosphere system (e.g., measured by aircraft or by space-borne sensors) in addition to the sky radiance measured at the surface, to improve the estimates of P11(Θ) and ω0. This work was based on employing the scalar radiative transfer (SRTE) in an iterative scheme in which trial functions P11(Θ) and ω0 were systematically varied until a pair was found that reproduced the measured radiances. As the SRTE was used, the polarization of the light field in the atmosphere was ignored. Here, we extend the earlier work by including polarization effects, i.e., we modify the algorithm by using the vector radiative transfer (VRTE) in the inversion. This allows estimation not only of P11(Θ) and ω0, but also of the 12 element of the aerosol-scattering Mueller matrix, P12(Θ).
Turn-Key Raman Lidar for Profiling Atmospheric Water Vapor, Clouds, and Aerosols at the US Southern Great Plains Climate Study Site
Authors: Goldsmith J. E. M. , Blair Forest H. , Bisson Scott E.
Published: February 2023

There are clearly identified scientific requirements for continuous profiling of atmospheric water vapor at the Department of Energy, Atmospheric Radiation Measurement program, Southern Great Plains CART (Cloud and Radiation Testbed) site in northern Oklahoma. Research conducted at several laboratories has demonstrated the suitability of Raman lidar for providing measurements that are an excellent match to those requirements. We have developed and installed a ruggedized Raman lidar system that resides permanently at the CART site, and that is computer automated to eliminate the requirements for operator interaction. In addition to the design goal of profiling water vapor through most of the troposphere during nighttime and through the boundary layer during daytime, the lidar provides quantitative characterizations of aerosols and clouds, including depolarization measurements for particle phase studies.
Cross-Correlation Techniques for Determining Absorbed Laser Lines in Remote Sensing
Authors: MacKerrow E.P. , Tieé J.J. , Schmitt M.J. , Whitehead M.J.
Published: February 2023

Multi-wavelength differential absorption lidar (DIAL) can be used for remote sensing of atmospheric effluents. If the composition of a remote chemical mixture is known apriori, the wavelengths used by the multi-wavelength lidar can be directly determined via absorption cross sections. Laser lines that are absorbed by a chemical, i.e. “on-lines”, are used along with a few non-absorbed laser lines, i.e. “off-lines”. If a remote chemical mixture is unknown, then measurements are usually made with as many different laser lines as possible to reveal a chemical signature. Only after the return signals at all of these lines are processed, averaged or smoothed, does one have a chance of determining which lines were actually absorbed by the remote chemical species. This can be a lengthy process depending upon the amount of pulse averaging needed to reduce random fluctuations and noise below the level of the chemical absorption signal. Further more, the wavelength variations of the target reflectivity create a fixed spectral pattern which is imposed on the atmospheric chemical absorption spectrum.
Nanosphere scattering simulations for efficient thin film solar cells
Authors: Sekhon Jagmeet Singh , Verma S S
Published: February 2023

The suitability of few commonly used plasmonic materials (e.g., Au, Ag and Cu) was demonstrated for enhancing the absorption efficiency of Si solar cells in the visible to near infrared region. It is summarized that the use of Cu nanosphere (with size more than Au) can help to make cheap solar cells with almost same efficiency as Au with a result of less reduction in photocurrent at lower wavelength regime in comparison to Ag. The results indicate that Cu could be more creditable for plasmonic solar cells in comparison to Ag and Au.
Single-mode Optical Waveguides using Fluorinated Polyimides
Authors: Matsuura Tohru , Ando Shinji , Matsui Shinsuke , Hirata Hirooki , Sasaki Shigekuni , Yamamoto Fumio
Published: February 2023

Polymer optical waveguides are attractive for economical and practical optoelectronic devices and interconnections in optical communication systems.1) High thermal stability should have the first priority in optical waveguides used for these purposes so as to provide compatibility with high-performance electronic device fabrication. Sullivan2) has reported thermally-stable ridge waveguides with a loss of 0.3 dB/cm at 0.83 μm fabricated with polyimide. We have synthesized new fluorinated polyimides with high optical transparency at the optical communication wavelengths of 1.3 and 1.5 μm.3) These polyimides are also being applied to low loss and multi-mode optical waveguides. However, single-mode optical waveguides are required for telecommunication systems to allow matching with single-mode optical fibers. This paper describes the first fabrication of single-mode optical waveguides using fluorinated polyimides and an evaluation of the waveguides.
Activation volumes associated with chromophore motion in corona poled guest-host polymers
Authors: Brower Shane C. , Hayden L. Michael
Published: February 2023

Non-linear optical (NLO) polymers have recently been the subject of considerable interest for applications in various electro-optic and photonic devices, including optical switches, light modulators, optical interconnects, and high density optical data storage devices.1,2 This interest is partly a result of their excellent optical properties: large optical non-linearity, low dielectric constants, and high transparency over a wide range of wavelengths.2,3,4,5 In addition, NLO polymers have the advantages of low cost and ease of processibility into thin films.4,5 However, the use of NLO polymers in commercial applications will require a material with a stable second order NLO susceptibility.
Fabrication of Vertically Stacked Coupler Using Electro-Optic Polymer
Authors: Hikita M. , Watanabe T. , Shuto Y. , Amano M. , Yoshimura R. , Tomaru S. , Kozawaguchi H.
Published: February 2023

Polymer waveguides have been of growing interest in the fields of integrated optics and optical interconnections. Vertical couplers and switches have been attracting considerable attention as key elements in three dimensional optical devices.1-4) This paper describes a vertically stacked coupler consisting of polymers incorporating electro-optic ( EO ) polymer fabricated using spinning, photolithography and reactive ion etching ( RIE ) techniques.5,6) This process notes it possible to control the spacing between two stacked waveguides and to design two waveguides independently. This gives advantages over previously reported methods such as photobleaching.7-9) Optical intensity modulation at 10 kHz is also demonstrated in a device with electrodes.
Asymmetric Fabry-Perot Electro-Optic Modulators Containing a Polymeric Film
Authors: Wang C.H. , Lloyd A.D. , Wherrett B.S. , Bone D.J. , Harvey T.G. , Ryan T.G. , Carter N.
Published: February 2023

Many organic polymeric materials have been developed that possess electro-optic coefficients exceeding that of LiNbO3 [1]. These materials lend themselves to incorporation within Fabry-Perot structures to form an electro-optic modulator [2], with potential for high modulation speeds and a wide range of commercially viable applications which are enabled by their ease of processing.
Light-Induced Second-Harmonic Generation in Azo-Dye Polymers
Authors: Charra F. , Kajzar F. , Fiorini C. , Nunzi J. M. , Raimond P.
Published: February 2023

The permanent all-optical poling of an azo-aromatic acrylic copolymer is experimentally demonstrated. The microscopic mechanism involves an orientational hole-burning and trans to cis isomerisation.
Saturable Absorption in Organic Semiconductor Doped Polymers
Authors: Carroll M. , Bloor D. , Cross G.H.
Published: February 2023

In recent years there has been great interest in semiconductor doped glasses with respect to their third order nonlinear optical, (nlo) properties [1]. Such systems have been found to have large third-order nonlinearities, and have exhibited enhancements in their nonlinearities when the semiconductor crystallites within the glass are very small, on the scale of tens of Angstroms. These enhancement effects have been attributed to quantum confinement effects which manifest themselves when the crystallite dimensions are reduced below the Bohr radius of the exciton associated with the nonlinearity. So far interest has centred on systems consisting of inorganic semiconductors such as CdS and CdSe[2] in host glasses and occasionally polymers [3]
Femtosecond difference transmission and difference phase spectra measured by frequency domain interferometer
Authors: Kobayashi Takayoshi , Tokunaga Eeiji
Published: February 2023

The pump-probe spectroscopy with a white-light continuum pulse has been playing major roles in femtosecond absorption spectroscopy because difference transmission spectra (DTS) can be obtained by using a multichannel spectrometer without scanning a probe wavelength. On the other hand, femtosecond phase spectroscopy, which is complementary to femtosecond absorption spectroscopy, is still in the primitive stage. This is mainly because there have been no methods by which difference phase spectra (DPS) can be obtained with a multichannel spectrometer as in the case of DTS.
Spectroscopy of Polymers with Multiple Nonlinear Techniques
Authors: Stegeman George I. , Torruellas William , Cha Myoungsik , Mukamel Shaul , Wang Hong Xiang , Takahashi Akira , Meth Jeff
Published: February 2023

The nonlinear mechanisms underlying the third order nonlinearity of any material can be studied by using nonlinear spectroscopy over an appropriate range of photon energy. Traditionally in the field of organic materials, third harmonic generation has been the principal probe used. A number of THG experiments have been successfully interpreted in terms of a limited number of contributing molecular states.[1] For conjugated polymers the best results to date have been obtained in terms of 4 "essential" states, the ground state (1Ag), the one photon o exciton state (1Bu), a dominant two photon state (mAg) and a second one photon state (nBu) which is weakly coupled to the ground state, but strongly coupled to the strong mAg two photon o state. In the past we have successfully interpreted our THG data using these four states.[1] However, when we extended our measurements to other nonlinear spectroscopic techniques such as non-degenerate three wave mixing and two photon absorption, we were no longer able to obtain satisfactory fits to all of our data simultaneously. We describe here a combined experiment-theory program in which we have studied the nonlinear spectra of a variety of nonlinear polymers in an effort to find a better interpretation of their nonlinear mechanisms.
Ultrafast Laser Characterization of Non-Linear Optical Chromophores
Authors: Lotshaw William T. , Staver P. Randall , Stewart K. Randall , Yakymyshyn Christopher P.
Published: February 2023

We have undertaken a program of femtosecond non-linear optical (NLO) spectroscopy in which the NLO properties of chromophores are interrogated both in solution (as isolated molecules) and in the polymeric or crystalline solid which will be used in actual photonic devices. The materials investigated are either χ2 or χ3 materials in their primary applications, although the results of these studies may indicate substantial cross-functionality. The laser source used for these studies, a synchronously pumped Ti:Sapphire laser which was developed in-house, was choosen for it’s broad tunability in a spectral region (680 nanometers to 1050 nanometers) which spans both nonresonant and resonant laser-material interactions in many candidate photonic materials. The short (nominally 40 femtoseconds at the sample position) pulse duration of this source coupled with optical heterodyne detection of the nonlinear optical response of the sample material permits interrogation of the complex χ3 over a bandwidth of nearly 700 cm−1 around the center frequency of the laser throughout the nearly 400 nanometer tuning range. Apart from the primary goal of merely measuring the magnitude and dispersion of the electronic and vibrational contributions to χ3 as an electronic resonance is approached, the more ambitious goal of these studies is to understand the effects of structure in the solid state upon the bulk NLO properties once the (isolated) molecular properties are ‘in hand’.
Modified Polyimide Polymers for Electro-Optic Applications
Authors: Prêtre Ph. , Kaatz P.G. , Bohren A. , Günter P. , Zysset B. , Ahlheim M. , Lehr F.
Published: February 2023

Novel amorphous nonlinear optical (NLO) polymers with modified polyimide backbones and functionalized azo chromophores have been synthesized for applications as electro-optic materials. The most attractive aspects of these polymers are the ease of modification of the NLO side-chain chromophores and the high thermal stability provided by glass transition temperatures in excess of 140 °C. The dispersion of the linear and nonlinear optical properties of these polymers has been determined. The time-temperature behaviour of the chromophore relaxation has been modeled to obtain estimates of the lifetimes of electro-optic devices using these polymers.
Photobleachable Donor-Acceptor-Donor Chromophores with Enhanced Thermal Stability
Authors: Ermer Susan , Leung Doris S. , Lovejoy Steven M. , Valley John F. , Stiller Marc
Published: February 2023

An important step in the realization of active optical interconnects is the development of poled electro-optic (EO) polymer materials stable to both manufacturing and end-use environments. These environments vary according to process and ultimate application, but many require longterm thermal stability to 125 °C and short excursions to 250 °C or higher.1 Our efforts with EO polymers have been directed toward thermally stable waveguide devices2 and polyimide-based guest-host material systems.3 We recently demonstrated a proof-of-principle all-polyimide triple stack Mach-Zehnder based on DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran) as the active chromophore in the core waveguide layer.4 The structure of DCM is shown in Figure 1(a). Advantages of DCM include low absorbance at device wavelengths, photobleachability, compatibility with polyimides and their polyamic acid precursors, and commercial ability at high purity. DCM is less than optimum in its thermal characteristics, however. It out-diffuses when heated above 220 °C for significant periods of time and it plasticizes the host material. This plasticization depresses the glass transition temperature Tg, and is detrimental to long-term stability of the poled state.
Molecular first hyperpolarisabilities of Bacteriorhodopsin and Retinal chromophores as determined from Hyper Rayleigh Scattering.
Authors: Hendrickx E. , Verbiest T. , Clays K. , Persoons A.
Published: February 2023

In previous papers [1.2,3] we demonstrated the feasibility of the Hyper Rayleigh Scattering (HRS) technique for the determination of the first molecular hyperpolarizability β in a macroscopically isotropic solution. This technique has several advantages over the more classic electric field induced second harmonic generation (EFISHG) technique because no electric field is required to break the centrosymmetry of the solution. Consequently, HRS allows for an easy and accurate determination of β of charged molecules and of molecules where β originates from octopolar charge distributions. Here we demonstrate the full strength of the HRS technique by measuring the first hyperpolarisability of a protein in a buffer solution as well as the (charged) protein chromophores in different solvents.
Polymeric Integrated Optical Circuits
Authors: Su W-F. A. , Weinstein S. J. , Cooper H. C. , Beuchel J. K.
Published: February 2023

Polymeric integrated multimode waveguides (100 µm × 125 µm × 3 in.) have been developed on conventional FR-4 epoxy printed circuit boards (PCBs) using UV curable polymers and negative photolithographic technology. Through molecular engineering, solventless UV curable guiding and cladding materials with appropriate optical and mechanical properties have been synthesized for waveguide applications in the visible and near-infrared wavelength regions. The solventless feature of these materials made them possible to fabricate thick waveguides in single process. Novel planarization technique have been developed to overcome the problems of surface waviness of the PCBs. Multimode (>75 microns) waveguides have been fabricated to distribute control signals to multiple transmit/receive (T/R) modules on large-array radar antennas. To date, waveguide structures with straight, curved, Y-split and tap geometries have been designed and fabricated successfully on PCBs; good light intensity outputs from Y-split and multiple-tap buses were obtained. This paper will discuss the materials and optical circuit fabrication of the waveguide structures and the results of laboratory tests using the optical buses for control signal distribution to T/R modules.
Nonlinear Optical Properties of O2-Doped and Photopolymerized C60
Authors: Flom S. R. , Pong R. G. S. , Bartoli F. J. , Kafafi Z. H. , Rao A. M. , Eklund P. C.
Published: February 2023

The interest in the nonlinear optical (NLO) properties of the fullerenes lies in their unique structure and symmetry which are responsible for the three-dimensional delocalization of π-electrons, a property often associated with enhanced NLO properties in organic materials. At NRL, our studies have focussed on the NLO behavior of pristine films of the fullerenes in the near-infrared1,2 and visible3 spectral region. Recently, the group at Kentucky succeeded in polymerizing C60 by irradiation of oxygen-free, face-centered-cubic films with visible or ultraviolet light.4 It was found that oxygen plays an important role in the photochemistry of C60. We have recently reported on the photo-assisted diffusion of O2 into solid C60 as well as its photo-oxidation.5,6 The present paper addresses the effect of altering the electronic/chemical structure, achieved by O2-doping and photopolymerization, on the NLO properties of C60 and the dynamics of the NLO response.
Interference Phenomena in Nonlinear Dielectrics
Authors: Kaatz P. , Nosbaum P. , Bosshard Ch. , Günter P.
Published: February 2023

The Maker fringe technique remains the most common and reliable method for evaluating relative magnitudes of nonlinear optical (NLO) susceptibilties. In this work we discuss generalizations of this technique to multilayer and multi-component determination of NLO susceptibilties for second (SHG) and/or third (THG) harmonic generation. Many authors have discussed SHG and/or THG from a single crystal or slab of NLO material for the case of neglible depletion of the fundamental wave, (see e.g. [1]).
Detection of Molecular Chirality using different Optical Second-Harmonic Generation Techniques
Authors: Stolle R. , Lohr F. , Marowsky G.
Published: February 2023

In the past, second-harmonic (SH) studies of monolayers have often been applied to systems with C∞
υ
-symmetry, in most cases to systems consisting of rodlike molecules [1]. These samples are axialsymmetric with respect to the surface and possess a mirror plane of symmetry normal to the surface. If the molecules are replaced by chiral molecules of one enantiomer, this mirror symmetry is broken and the system C∞-symmetry. In the following, this is called surface chirality. Because these monomolecular films are very thin, this symmetry break can hardly be detected using linear optical techniques such as optical activity measurements. However, if the molecular chirality influences the part of the nonlinear structure responsible for SH generation, surface chirality can be detected by using nonlinear optical techniques.
In situ RHEED observation of MBE growth of organic thin films
Authors: Ishibashi Tadashi , Tamura Shin'ichiro , Seto Jun'etsu , Hara Masahiko , Sasabe Hiroyuki , Knoll Wolfgang
Published: February 2023

Studies on molecular beam epitaxial growth for organic molecules (OMBE) have been attracting attentions as a new fabrication method for preparation of ultra-thin films of organic molecules. Molecular beam epitaxy (MBE) has been developed as a deposition technique for the controlled growth of atomically flat multilayer structures. Recently, this method has been applied to organic materials, while the mechanism of the growth has not been thoroughly understood compared to that of semiconductor. In this report, the growth mechanism of Lead Phthalocyanine (PbPc) thin films onto highly oriented pyrolytic graphite (HOPG) substrate by OMBE method was investigated using in situ refraction high energy electron diffraction (RHEED). RHEED has been widely used for in situ monitoring of the thin film MBE growth. The intensity of the RHEED specular beam spot oscillates according to the layer-by-layer growth[1]. In 1981, Joyce et.al. observed an oscillated phenomena of RHEED intensity with growth of semiconductor for the first time[2]. After that, a lot of work in the semiconductor field have been reported and developed. Although application for organic materials is expected, so far RHEED oscillation studies have only been reported for Copper Phthalocyanine (CuPc) on MoS2 substrate[3]. Therefore, we explored the possibilities of using in situ RHEED observations to investigate the OMBE growth mechanism of PbPc on HOPG system.
Fabrication of Out-of-Plane Branching Mirrors on Polymer Channel Waveguide
Authors: Kagami Manabu , Hasegawa Kazuo , Ito Hiroshi
Published: February 2023

Noncrystalline polymers are suitable as a low cost and high-power optical waveguide material because they have little optical damage. Optical waveguides with large core and high-A (LCHD) are effective for a high-power application, because of low power density and easy assembly. High optical power is necessary for driving an optical amplifier1 or optical devices with nonlinear optical effects or light-to-heat conversion.2 To couple these devices utilizing the waveguide, out-of-plane branching mirrors are useful (Fig. 1). These mirrors are also applicable to the coupling of optical fiber or OEIC chips3 with the optical waveguide. A channel waveguide and the mirror are usually fabricated by different mask processes.4 These complicated processes require precise mask alignment procedure. In this report, we propose a process of simultaneously fabricating out-of-plane branching mirrors and polymer channel waveguides from a slab structure by reactive ion etching (RIE).
Structural and solvatochromic studies of a series of chromophoric TCNQ derivatives with large second order nonlinearities.
Authors: Szablewski Marek , Thomas Philip , Cross Graham , Cole Jacqueline
Published: February 2023

As a result of our discovery of a novel reaction of TCNQ with triethylamine1 which led to the synthesis of DEMI (structure I, fig. 1)2, we have prepared a range of similar adducts of TCNQ with tertiary ethyl amines (structures I - VII). All of these adducts have similar structural components, a dicyanomethanide group separated from an electron deficient amino moiety by an aromatic/quinoidal ring and a "conjugated" π system. The spectral properties of these species are therefore very similar, comprising a broad charge transfer band with very little absorption to either side of it, in fact a "blue window" centred on 460 nm (fig. 2, below). As a result of their charge separated ground state, these molecules have large theoretical μβ(0) products, indicative of a high second order nonlinearity. The molecular figure of merit, μβ(0) has been calculated for I as -17,500 x 10-48esu. Three TCNQ adducts prepared by conventional reactions of TCNQ with secondary amines6 are included (IIX - X) for comparison purposes. The μβ(0) product of X has been determined7 to be -840 x 10-48 esu, assuming a calculated μ of 3.5 D. This material is however extremely insoluble and therefore difficult to work with.
Preparation, Optical Spectroscopy, and Fluorescence of Molecular Organic Composites for Light-Emitting Diodes
Authors: Sarkas Harry. W. , Merritt Charles D. , Kafafi Zakya H.
Published: February 2023

Electroluminescence from small organic molecules has been known for some time. Thirty years ago, Helfrich and Schneider reported blue-violet electroluminescence in anthracene with an external quantum efficiency as high as 8%.1 This quantum efficiency is much better than that for the best polymer-based light-emitting diode (LED) reported to date.2 In spite of the superior quantum efficiency of molecular-based electroluminescent devices, no major progress was achieved until fairly recently when Tang and VanSlyke reported the first low-voltage organic LED with an external quantum efficiency of 1% (number of photons per electron).3 The emitting layer in this device consists of a thin layer of the metal complex, tris (8-hydroxyquinolinato) aluminum (AlQ3). Later, Littman and Martie showed an enhancement in the electroluminescence quantum efficiency of AlQ3 by doping it with the highly fluorescent laser dyes, Coumarin 540, Coumarin 343, and DCM.4 The paper focuses on a new class of organic composites consisting of highly fluorescent guest molecules dispersed in AlQ3. The electronic and optical properties of organic nanostructures based on these materials are studied, as functions of the luminescent center concentration, via optical and fluorescence spectroscopies. Photoluminescence quantum yields are measured and used to probe the efficiency of energy transfer between host and guest molecules.