Simplified Homodyne Detection for FM Chirped Lidar

The investigation of global warming requires more sensitive altimeters to better map the global ice reserves. A homodyne detection scheme for FM chirped lidar is developed in which dechirping is performed in the optical domain, simplifying both the optical and the RF circuits compared to heterodyne detection. Experiments show that the receiver sensitivity approaches the quantum limit and surpasses the performance of direct and heterodyne detection. In addition, the required electrical bandwidth of the photodiode and receiver RF circuitry are both significantly reduced, facilitating the use of large area photodetector arrays. A field trial using a 5"-aperture diameter telescope and a 370-m target range verified the sensitivity estimation and demonstrates the feasibility of this technique. The problem of homodyne carrier fading is addressed by incorporating a phase diversity receiver using a 90-degree optical coupler. Finally, an outline of the future direction of research is given

Tunable excitation source for coherent Raman spectroscopy based on a single fiber laser

This is the published version. ©Copyright 2011 AIP PublishingWe demonstrate a wavelength tunable optical excitation source for coherent Raman scattering (CRS) spectroscopy based on a single femtosecondfiber laser. Electrically controlled wavelength tuning of Stokes optical pulses was achieved with soliton self frequency shift in an optical fiber, and linear frequency chirping was applied to both the pump and the Stokes waves to significantly improve the spectral resolution. The coherent anti-Stokes Raman scattering (CARS)spectrum of cyclohexane was measured and vibrational resonant Raman peaks separated by 70 cm−1 were clearly resolved. Single laser-based tunable excitation may greatly simplify CRS measurements and extend the practicality of CRS microscopy

Fiber Laser Based Nonlinear Spectroscopy

To date, nonlinear spectroscopy has been considered an expensive technique and confined mostly to experimental laboratory settings. Over recent years, optical-fiber lasers that are highly reliable, simple to operate and relatively inexpensive have become commercially available, removing one of the major obstacles to widespread utilization of nonlinear optical measurement in biochemistry. However, fiber lasers generally offer relatively low output power compared to lasers traditionally used for nonlinear spectroscopy, and much more careful design is necessary to meet the excitation power thresholds for nonlinear signal generation. On the other hand, reducing the excitation intensity provides a much more suitable level of user-safety, minimizes damage to biological samples and reduces interference with intrinsic chemical processes. Compared to traditional spectroscopy systems, the complexity of nonlinear spectroscopy and imaging instruments must be drastically reduced for them to become practical. A nonlinear spectroscopy tool based on a single fiber laser, with electrically controlled wavelength-tuning and spectral resolution enhanced by a pulse shaping technique, will efficiently produce optical excitation that allows quantitative measurement of important nonlinear optical properties of materials. The work represented here encompasses the theory and design of a nonlinear spectroscopy and imaging system of the simplest architecture possible, while solving the difficult underlying design challenges. With this goal, the following report introduces the theories of nonlinear optical propagation relevant to the design of a wavelength tunable system for nonlinear spectroscopy applications, specifically Coherent Anti-Stokes Spectroscopy (CARS) and Förster Resonance Energy Transfer (FRET). It includes a detailed study of nonlinear propagation of optical solitons using various analysis techniques. A solution of the generalized nonlinear Schrödinger equation using the split-step Fourier method is demonstrated and investigation of optical soliton propagation in fibers is carried out. Other numerical methods, such as the finite difference time domain approach and spectral-split step Fourier methods are also described and compared. Numerical results are contrasted with various measurements of wavelength shifted solitons. Both CARS and FRET test-bed designs and experiments are presented, representing two valuable biochemical measurement applications. Two-photon excitation experiments with a simplified calibration process for quantitative FRET measurement were conducted on calmodulin proteins modified with fluorescent dyes, as well as modified enhanced green fluorescent protein. The resulting new FRET efficiency measurements showed agreement with those of alternative techniques which are slower and can involve destruction of the sample. In the second major application of the nonlinear spectroscopy system, CARS measurement with enhanced spectral resolution was conducted on cyclohexane as well as on samples of mouse brain tissue containing lipids with Raman resonances. The measurements of cyclohexane verified the ability of the system to precisely determine its Raman resonances, thus providing a benchmark within a similar spectral range for biological materials which have weaker Raman signal responses. The improvement of spectral resolution (resonance frequency selectivity), was also demonstrated by measuring the closely-spaced resonances of cyclohexane. Finally, CARS measurements were also made on samples of mouse brain tissue which has a lipids-based Raman signature. The CARS spectrum of the lipid resonances matched well with other cited studies. The imaging of mouse brain tissue with Raman resonance contrast was also partially achieved, but it was hindered by low signal to noise ratio and limitations of the control hardware that led to some dropout of the CARS signal due to power coupling fluctuations. Nevertheless, these difficulties can be straightforwardly addressed by refinement of the wavelength tuning electronics. In conclusion, it is hoped that these efforts will lead to greater accessibility and use of CARS, FRET and other nonlinear spectral measurement instruments, in line with the promising advances in optics and laser technology

Islamic Applications of Automatic Question-Answering

search engine aims to retrieve full documents whereas a question answering system aims to extract the exact answer. A question answering system involves the process of accepting a NL (Natural Language) question, analyzing, and processing to match against a knowledge base to generate the right answer from documents for users. For the Holy Quran this involves accepting the NL question and processing it to retrieve the right verse or verses from our Quran knowledge base. Question answering systems can use two types of algorithms: rule based techniques and/or AI (Artificial Intelligence) based techniques. Question Answering systems have three main components: question classification, information retrieval and answer extraction. We present a rule-based system for the Holy Quran that retrieves the right verse(s) from the Holy Quran instead of generating NL answers. We use a java program to extract the answer from a MS-Access database which contains our knowledge base for our Quran question answering system. We find that the system gives better results for the question after improving the system by removing stop words

Studi Awal Makrozoobentos di Kawasan Wisata Sungai Kalimas, Monumen Kapal Selam Surabaya

Sungai merupakan salah satu ekosistem perairan darat yang memiliki banyak kompleksitas dari penyusun organismenya maupun ancaman terhadap keberlangsungan ekosistem hayati. Salah satu faktor biotik yang dapat dijadikan indikator kesehatan sungai adalah makrozoobentos. Penelitian ini bertujuan untuk mengetahui jenis-jenis makrozoobentos di kawasan wisata sungai Kalimas, Monumen Kapal Selam (Monkasel) Surabaya sebagai studi awal biodiversitas dan kompleksitas struktur trofuk di Kalimas Surabaya. Pengambilan sampel dilakukan di sepanjang sungai sisi Monkasel menggunakan Ekman Grab (Buttom grab). Identifikasi dilakukan di Laboratorium Ekologi, Biologi Fakultas Sains, ITS dan di analisa menggunakan indeks biodiversitas. Berdasarkan hasil, diketahui bahwa makrozoobentos yang ditemukan adalah 8 spesies dengan nilai indeks biodiversitasnya 0,82

Fiber Laser Based Two-Photon FRET Measurement of Calmodulin and mCherry-E0GFP Proteins

This is the peer reviewed version of the following article: Adany, P., Johnson, C. K. and Hui, R. (2012), Fiber laser based two-photon fret measurement of calmodulin and mcherry-E0GFP proteins. Microsc. Res. Tech., 75: 837–843. doi:10.1002/jemt.22002, which has been published in final form at http://doi.org/10.1002/jemt.22002. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The speed and accuracy of Förster Resonance Energy Transfer (FRET) measurements can be improved by rapidly alternating excitation wavelengths between the donor and acceptor fluorophore. We demonstrate FRET efficiency measurements based on a fiber laser and photonic crystal fiber as the source for two-photon excitation (TPE). This system offers the potential for rapid wavelength switching with the benefits of axial optical sectioning and improved penetration depth provided by TPE. Correction of FRET signals for cross excitation and cross emission was achieved by switching the excitation wavelength with an electrically controlled modulator. Measurement speed was primarily limited by integration times required to measure fluorescence. Using this system, we measured the FRET efficiency of calmodulin labeled with Alexa Fluor 488 and Texas Red dyes. In addition, we measured two-photon induced FRET in an E0GFP-mCherry protein construct. Results from one-photon and two-photon excitation are compared to validate the rapid wavelength switched two-photon measurements

Two-frequency CARS imaging by switching fiber laser excitation

This is the peer reviewed version of the following article: Rentchler EC, Xie R, Hui R, JohnsonCK. Two-frequency CARS imaging by switching fiber laser excitation. Microsc Res Tech. 2018;81:413–418. https://doi.org/10. 1002/jemt.22993, which has been published in final form at https://doi.org/10.1002/jemt.22993. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.To fully exploit the power of coherent Raman imaging, techniques are needed to image more than one vibrational frequency simultaneously. We describe a method for switching between two vibrational frequencies based on a single fiber‐laser source. Stokes pulses were generated by soliton self‐frequency shifting in a photonic crystal fiber. Pump and Stokes pulses were stretched to enhance vibrational resolution by spectral focusing. Stokes pulses were switched between two wavelengths on the millisecond time scale by a liquid‐crystal retarder. Proof‐of‐principle is demonstrated by coherent anti‐Stokes Raman imaging of polystyrene beads embedded in a poly(methyl methacrylate) (PMMA) matrix. The Stokes shift was switched between 3,050 cm−1, where polystyrene has a Raman transition, and 2,950 cm−1, where both polystyrene and PMMA have Raman resonances. The method can be extended to multiple vibrational modes

Tunable excitation source for coherent Raman spectroscopy based on a single fiber laser

This is the publisher's version, also available electronically from http://scitation.aip.org/content/aip/journal/apl/99/18/10.1063/1.3657529.We demonstrate a wavelength tunable optical excitation source for coherent Raman scattering (CRS) spectroscopy based on a single femtosecondfiber laser. Electrically controlled wavelength tuning of Stokes optical pulses was achieved with soliton self frequency shift in an optical fiber, and linear frequency chirping was applied to both the pump and the Stokes waves to significantly improve the spectral resolution. The coherent anti-Stokes Raman scattering (CARS)spectrum of cyclohexane was measured and vibrational resonant Raman peaks separated by 70 cm−1 were clearly resolved. Single laser-based tunable excitation may greatly simplify CRS measurements and extend the practicality of CRS microscopy