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Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

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Early Posting

Accepted papers to appear in an upcoming issue

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August


Fourier filter augmented with trainer histograms

  • Kaveh Heidary
  • received 07/11/2014; accepted 08/20/2014; posted 08/21/2014; Doc. ID 216816
  • [full text: PDF (425) KB)]
  • Abstract: This paper describes a computationally efficient method for boosting the performance of correlation filters. The correlation filter is augmented with an array of histograms and the associated affinity numbers, obtained from the training image set utilized in construction of the filter. In the operation phase, histograms of sensor images are examined only at the image neighborhoods where the correlation filter provides initial indications of target occurrence. The presence of target is affirmed at image locations that pass both the peak cross correlation and histogram tests. Results of numerous experiments demonstrate that reinforcement of the spatial correlation filter with the trainer histograms leads to more robust Fourier filters for target detection and classification.

Keywords (OCIS):

  • (100.4550) Image processing : Correlators
  • (100.3008) Image processing : Image recognition, algorithms and filters
  • (100.4999) Image processing : Pattern recognition, target tracking

Super resolved passive imaging of remote moving object on top of sparse unknown background

  • Asaf Ilovitsh and Zeev Zalevsky
  • received 07/24/2014; accepted 08/20/2014; posted 08/21/2014; Doc. ID 217754
  • [full text: PDF (892) KB)]
  • Abstract: A new passive method for improving the contour resolution of a moving object, and overcoming the diffraction limit without having any a priori information is presented. The resolution improvement is obtained using a sequence of low resolution images taken at different positions of an unknown object moving in respect to an unknown background. The super resolving process has two steps. First, a high resolution estimation of the background is reconstructed using deconvolution algorithm. Second, the captured set of low resolution images are decoded by the deconvolved background, and a high resolution image of the object’s contour is generated.

Keywords (OCIS):

  • (100.2000) Image processing : Digital image processing
  • (100.6640) Image processing : Superresolution
  • (280.0280) Remote sensing and sensors : Remote sensing and sensors

Fully-phase image encryption using double random- structured phase masks in gyrator domain

  • Hukum Singh, A. Yadav, Sunanda Vashisth, and Kehar Singh
  • received 07/10/2014; accepted 08/20/2014; posted 08/22/2014; Doc. ID 216730
  • [full text: PDF (3525) KB)]
  • Abstract: We propose a method for fully-phase image encryption based on double random-structured phase mask encoding in the gyrator transform (GT) domain. The security of the system is strengthened by parameters used in the construction of structured phase mask (SPM) based on devil’s vortex Fresnel lens (DVFL). The input image is recovered by using the correct parameters of the SPMs, transform orders of the GT, and conjugate of the random phase masks (RPMs). The use of a DVFL-based SPM enhances security by increasing the key space for encryption, and also overcomes the problem of axis-alignment associated with an optical set-up. The proposed scheme can also be implemented optically. The computed values of mean-squared-error (MSE) between the retrieved and the original image, show the efficacy of the proposed scheme. We have also investigated the scheme’s sensitivity to the encryption parameters, and robustness against occlusion and multiplicative Gaussian noise attacks.

Keywords (OCIS):

  • (100.2960) Image processing : Image analysis
  • (100.3010) Image processing : Image reconstruction techniques
  • (100.5070) Image processing : Phase retrieval
  • (100.5090) Image processing : Phase-only filters
  • (110.2350) Imaging systems : Fiber optics imaging
  • (110.2990) Imaging systems : Image formation theory

(SANDIA) Precision alignment of integrated optics in hybrid microsystems

  • Amber Young, Jeff Hunker, A. Ellis, Sally Samora, Joel Wendt, Peter Maunz, and Daniel Stick
  • received 07/02/2014; accepted 08/20/2014; posted 08/20/2014; Doc. ID 208006
  • [full text: PDF (1114) KB)]
  • Abstract: We achieve sub-micron precision in the integration of micro-optics with surface electrode ion traps. The high-precision alignment is accomplished using off-axis linear Fresnel zone plates (FZPs). Four pairs of FZPs are fabricated on the optics chip containing the high-numerical aperture (NA) micro-lens, a diffractive optical element (DOE). The four pairs of FZPs enable alignment in all six-degrees of freedom. Four corresponding alignment rulers are etched in the top metal layer of the ion trap, enabling quantification of misalignment. The integration of optics for efficient light delivery and the collection of fluorescence from trapped ions is key to achieving scalability in quantum information processing. An accurate and precise approach to the integration of DOEs advances the scalability of surface electrode ion traps and many other hybrid microsystems.

Keywords (OCIS):

  • (130.0130) Integrated optics : Integrated optics
  • (220.1140) Optical design and fabrication : Alignment
  • (050.1965) Diffraction and gratings : Diffractive lenses
  • (130.6622) Integrated optics : Subsystem integration and techniques
  • (130.3990) Integrated optics : Micro-optical devices

Engineering chromatic dispersion and effective nonlinearity in dual slot waveguide

  • Jing Yan, Yan Liu, and Genquan Han
  • received 06/30/2014; accepted 08/20/2014; posted 08/20/2014; Doc. ID 214853
  • [full text: PDF (657) KB)]
  • Abstract: In this paper, we propose a new dual slot based on rib-like structure, which exhibits a flat and near-zero dispersion over 198-nm-wide wavelength range. Chromatic dispersion of dual slot silicon (Si) waveguide is mainly determined by waveguide dispersion due to the manipulating mode effective area rather than by the material dispersion. Moreover, the nonlinear coefficient and effective mode area of the waveguide are also explored in detail. A nonlinear coefficient of 1460 /m/W at 1550 nm is achieved, which is 10 times larger than that of the Si rib waveguide. By changing different waveguide variables, both the dispersion and nonlinear coefficient can be tailored, thus enabling the potentials for a highly nonlinear waveguide with uniform dispersion over a wide wavelength range, which could benefit the performance of broadband optical signal system.

Keywords (OCIS):

  • (130.0130) Integrated optics : Integrated optics
  • (190.0190) Nonlinear optics : Nonlinear optics
  • (230.7370) Optical devices : Waveguides

Optical interference-based multiple-image encryption using spherical wave illumination and gyrator transform

  • Muhammad Abuturab
  • received 07/28/2014; accepted 08/20/2014; posted 08/28/2014; Doc. ID 219944
  • [full text: PDF (12287) KB)]
  • Abstract: A new optical interference-based multiple-image encryption using spherical wave illumination and gyrator transform is proposed. In this proposal, each secret color image is divided into normalized red, green and blue component images and independently encoded into corresponding phase-only component images. Then each phase-only component image of all the images are combined together to produce a single-phase only component image as an input component image, which is bounded with a random phase mask to form a complex image. The two phase-only masks are analytically obtained from the inverse Fourier transformation of the complex image. The host image is chosen as the first phase-only mask and the complex image hidden in host image is regarded as the second phase-only mask. The spherical wave is generated to simultaneously illuminate phase-only masks. Then two modulated masks are gyrator transformed. The corresponding transformed images are phase truncated to obtain encrypted images, and amplitude truncated to construct decryption keys. The decryption keys, angles of gyrator transform, wavelength and radius of the spherical wave, and individual decryption keys for authorized users are very sensitive keys, which enhance the security layers of the system. The proposed system can be implemented by using opto-electronic architecture. Numerical simulation results demonstrate the flexibility of the system.

Keywords (OCIS):

  • (050.0050) Diffraction and gratings : Diffraction and gratings
  • (070.0070) Fourier optics and signal processing : Fourier optics and signal processing
  • (100.2000) Image processing : Digital image processing
  • (070.2615) Fourier optics and signal processing : Frequency filtering
  • (060.4785) Fiber optics and optical communications : Optical security and encryption

Broadband Infrared Beam Splitter for Spaceborne Interferometric InfraRed Sounder

  • Tianyan Yu, Dingquan Liu, and Yang Qin
  • received 04/11/2014; accepted 08/19/2014; posted 08/25/2014; Doc. ID 209936
  • [full text: PDF (466) KB)]
  • Abstract: Broadband infrared beam splitter on ZnSe substrate used for Spaceborne Interferometric InfraRed Sounder (SIIRS) is studied in the spectral range of 4.44-15μm. Both broadband antireflection coating and broadband beam-splitter coating in this beam splitter are designed and tested. To optimized the optical properties and the stability of the beam splitter, suitable infrared materials were selected and improved deposition techniques are applied. The designed structures matched experimental data well and the properties of the beam splitter meet the application specification of SIIRS.

Keywords (OCIS):

  • (310.1210) Thin films : Antireflection coatings
  • (310.1620) Thin films : Interference coatings
  • (310.1860) Thin films : Deposition and fabrication
  • (310.3840) Thin films : Materials and process characterization
  • (310.6860) Thin films : Thin films, optical properties
  • (310.4165) Thin films : Multilayer design

Control of mid-spatial frequency errors considering the pad groove feature in smoothing polishing process

  • Xuqing Nie, Shengyi Li, Hao Hu, and Qi Li
  • received 07/08/2014; accepted 08/18/2014; posted 08/21/2014; Doc. ID 216569
  • [full text: PDF (1637) KB)]
  • Abstract: Mid-spatial frequency error (MSFR) should be strictly controlled in modern optical systems. As an effective approach to suppress the MSFR, smoothing polishing (SP) process is not easy to handle because it can be affected by many factors. This paper mainly focuses on the influence of pad groove which has not been researched yet. SP process is introduced and the important role of pad groove is explained in detail. Relationship between the contact pressure distribution and groove feature including groove section type, groove width, and groove depth is established, and the optimized result is achieved with finite element method. The different kinds of groove patterns are compared utilizing the numerical superposition method established scrupulously. The optimal groove is applied in the verification experiment conducted on a self-developed SP machine. The RMS value of the MSFR after SP process is diminished from 2.38 nm to 0.68 nm, which reveals that the selected pad can smooth out the MSFR to a great extent with proper SP parameters, while the newly generated MSFR due to the groove can be suppressed to a very low magnitude.

Keywords (OCIS):

  • (220.0220) Optical design and fabrication : Optical design and fabrication
  • (220.4610) Optical design and fabrication : Optical fabrication
  • (220.5450) Optical design and fabrication : Polishing

Flame spectra-temperature estimation based on a color imaging camera and a spectral reconstruction technique

  • Carlos Toro N., Luis Arias P., Sergio Torres, and Daniel Sbarbaro
  • received 05/23/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 212493
  • [full text: PDF (1841) KB)]
  • Abstract: In this paper, a low cost practical pixel-based flame spectrum and temperature estimation system based on flame color images is proposed. A spectral resolution of ~0.4nm is achieved with an optical system formed by a color camera, a linear model, a flame’s spectral training data and a spectral reconstruction procedure. As a proof of concept, the estimated spectra is compared to local measurements performed with a commercial spectrometer. In order to estimate the absolute flame temperature maps, two radiometric images at different wavelengths are reconstructed and the two color pyrometry method is applied. Experiments show errors of about 4.0% over the estimated temperature, making this system a practical tool for flame sensing in combustion process monitoring.

Keywords (OCIS):

  • (110.0110) Imaging systems : Imaging systems
  • (120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
  • (120.4630) Instrumentation, measurement, and metrology : Optical inspection
  • (280.2470) Remote sensing and sensors : Flames

Wavefront aberrations of x-ray dynamical diffraction beams

  • Keliang Liao, Youli Hong, and Weifan Sheng
  • received 07/02/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 215182
  • [full text: PDF (827) KB)]
  • Abstract: The effects of dynamical diffraction in x-ray diffractive optics with large numerical aperture render the wavefront distortion difficult to be described by using the aberration polynomials, yet knowledge of them plays an important role in a vast variety of scientific problems ranging from optical testing to adaptive optics. Although the diffraction theory of optical aberrations was established decades ago, its application in the area of x-ray dynamical diffraction theory is still lacking. Here, we conduct a theoretical study on the aberration properties of x-ray dynamical diffraction beams. By treating the modulus of the complex envelope as the amplitude weight function in the orthogonalization procedure, we generalize the non-recursive matrix method [Opt. Lett. 32, 74-76 (2007)] for the determination of orthonormal aberration polynomials, wherein Zernike-DDT and Legendre-DDT polynomials are proposed. As an example, we investigate the aberration evolution inside a tilted multilayer Laue lens (MLL). The corresponding Legendre-DDT polynomials are obtained numerically, which represent balanced aberrations yielding minimum variance of the classical aberrations of an anamorphic optical system. The balancing of classical aberrations and their standard deviations are discussed. We also present the Strehl ratio of the primary and secondary balanced aberrations.

Keywords (OCIS):

  • (220.1010) Optical design and fabrication : Aberrations (global)
  • (340.7460) X-ray optics : X-ray microscopy
  • (080.1005) Geometric optics : Aberration expansions

Experimental Observation of Different Soliton-types in A Net-normal Group-dispersion Fiber Laser

  • Qiangzhou Rong, Zhongyao Feng, Xueguang Qiao, Zhihua Shao, and Dan Su
  • received 07/08/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 216551
  • [full text: PDF (674) KB)]
  • Abstract: Different soliton-types are observed in a net-normal group-dispersion fiber laser based on nonlinear polarization rotation (NPR) for passively mode locking. The proposed laser can deliver dispersion-managed (DM) soliton, typical dissipation solitons (DS) and quasi-harmonic mode-locked pulse (QHMLP), soliton bundle, and especially dark pulse by only appropriately adjusting the linear cavity phase delay bias (LCPDB) using one polarization controller (PC) at the fixed pump power. These nonlinear waves show different features, including the spectral shapes and time traces. The experimental observations show that the five soliton-types could exist in the same laser cavity, which implies that integrable systems, dissipative system, and dark pulse regime can transfer and be switched in a passively mode-locked laser. Our studies not only verify the numeral simulation of the different soliton-types formation in a net-normal group-dispersion operation but also provide insight into Ginzburg-Landau equation (GLE) systems.

Keywords (OCIS):

  • (140.0140) Lasers and laser optics : Lasers and laser optics
  • (140.3500) Lasers and laser optics : Lasers, erbium
  • (140.3510) Lasers and laser optics : Lasers, fiber

Analyzing the effect of synthetic scene resolution, sampling interval and signal-to-noise ratio on hyperspectral imaging sensor simulation

  • Dongxing Tao, Huijie Zhao, Guorui Jia, and Yan Yuan
  • received 04/04/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 204627
  • [full text: PDF (493) KB)]
  • Abstract: Sensor simulation model is an important tool for the design of new Earth imaging system. As the input of the model, the characters of synthetic spectral scene image data cube (SSSIDC) play an important role for the accuracy of the simulation. Based on a general sensor simulation model, the effect of SSSIDC resolution, sampling interval (SI) and signal-to-noise ratio (SNR) on simulated data is analyzed respectively. Analysis shows that the simulated data characters are the function of model parameters and SSSIDC characters. The result can be used for evaluating the errors of simulated data, giving criteria for scene image synthesis, and designing appropriate model parameters for expected simulation. Some simulation experiments are designed to demonstrate the analysis, and the results show that the analysis is valid.

Keywords (OCIS):

  • (280.0280) Remote sensing and sensors : Remote sensing and sensors
  • (280.4788) Remote sensing and sensors : Optical sensing and sensors
  • (280.4991) Remote sensing and sensors : Passive remote sensing

Real-time infrared target tracking based on l₁ minimization and compressive features

  • Ying Li, Pengcheng Li, and Qiang Shen
  • received 08/14/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 209650
  • [full text: PDF (2870) KB)]
  • Abstract: Target tracking in infrared (IR) imagery is a challenging task due to low resolution, low signal-to-noise ratios (SNRs), occlusion, obscurity and poor target visibility. This task could be even more difficult when real-time requirements have to be taken into account. This paper presents a real-time infrared target tracking under complex conditions based on l₁ minimization and compressive features. Firstly, we adopt a sparse measurement matrix to project the high dimensional Harr-like features to low dimensional features that are applied to the appearance modeling. This appearance model allows significant reduction in the computational cost of the target tracking phase. Then, the appearance model is introduced into the framework of the popular l₁ tracker. Each infrared target candidate is represented by the appearance template based on the structure of sparse representation. Finally, the candidate which has the minimum reconstruction error is selected as the tracking result. The proposed tracking method can combine the real-time advantages of the compressive tracking and the robustness of the l₁ tracker. Experimental results on challenging infrared image sequences including both aerial targets and ground targets show that the proposed algorithm has better robustness and real-time performance in comparison with two latest state-of-the-art tracking algorithms.

Keywords (OCIS):

  • (100.0100) Image processing : Image processing
  • (100.2000) Image processing : Digital image processing
  • (100.4993) Image processing : Pattern recognition, Baysian processors
  • (100.4999) Image processing : Pattern recognition, target tracking

Analysis of Nonlinear Optical and Dynamic Gain Effects of Moderate-Power, Pulse-Position-Modulated, Erbium-Doped Fiber Amplifiers for Deep-Space Applications

  • Haomin Yao, Malcolm Wright, and John Marciante
  • received 05/05/2014; accepted 08/18/2014; posted 08/19/2014; Doc. ID 211413
  • [full text: PDF (751) KB)]
  • Abstract: Lasers for use in deep-space applications such as interplanetary optical communications employ multi-Watt resonantly-pumped dual-clad erbium-doped fiber amplifiers and the pulse-position modulation scheme. Nonlinear optical effects and dynamic gain effects often impair their performance and limit their operational range. These effects are analyzed theoretically and numerically with a time-dependent two-level propagation model, respectively. Self-phase modulation and stimulated Raman scattering are found to limit the usable data format space. In operational regimes free from nonlinear effects, dynamic gain effects such as the variation in the output pulse energy and square-pulse distortion are quantified. Both are found to primarily depend on the symbol duration and can be as large as 28% and 21%, respectively.

Keywords (OCIS):

  • (060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
  • (140.3280) Lasers and laser optics : Laser amplifiers
  • (140.3500) Lasers and laser optics : Lasers, erbium
  • (230.2285) Optical devices : Fiber devices and optical amplifiers
  • (200.2605) Optics in computing : Free-space optical communication

Fano resonance properties of gold nanocrescent arrays

  • Yingzhou Huang, Zhongwei Liao, Zhou Bingpu, Shunbo Li, Shuxia Wang, and Weijia Wen
  • received 07/22/2014; accepted 08/18/2014; posted 08/26/2014; Doc. ID 217500
  • [full text: PDF (856) KB)]
  • Abstract: The Fano resonance induced by symmetry breaking could improve the sensitivity of localized surface plasmon resonance sensor. In this work, the spectra of gold nanocrescent arrays are measured and confirmed by simulation results through finite element method (FEM). The Fano resonance presented in the spectra could be modulated by the symmetry breaking with different waist widths, which are understood through plasmonic hybridization theory with the help of surface charge distribution. Our results indicate the Fano lineshape is generated by the coherent coupling of quadrupole plasmon mode QH of nanohole and antibonding plasmon mode DAB of nanocrescent. Finally, the high figure of merit (FoM = 1.6~3.5) of Q mode in visible region illustrates this nanocrescent Fano sensor is of great application value in the biological and chemical scientific fields.

Keywords (OCIS):

  • (240.6680) Optics at surfaces : Surface plasmons
  • (280.4788) Remote sensing and sensors : Optical sensing and sensors
  • (250.5403) Optoelectronics : Plasmonics

Investigation of subwavelength grating structure for enhanced surface plasmon resonance detection

  • M. Tahmasebpour, M. Bahrami, and A. Asgari
  • received 04/15/2014; accepted 08/18/2014; posted 08/18/2014; Doc. ID 210104
  • [full text: PDF (4719) KB)]
  • Abstract: A metallic subwavelength grating structure built on a thin gold film is studied for surface plasmon resonance (SPR) detection of refractive index variations of biological buffer solutions. By employing the finite element analysis as a numerical method, characteristics of the angle interrogated SPR sensor were calculated and discussed in broad operating wavelength varying from visible to near–infrared (NIR). The effects of grating structural parameters such as grating depth, grating period and grating fill factor in different operating wavelengths have been evaluated on the sensor performance parameters of sensitivity, full width at half minimum (FWHM), minimum reflectance at resonance (MRR) and resonance angle. Numerical results indicate that adjusting grating geometrical parameters can enhance the performance parameters of the sensor specially in the NIR wavelengths. The enhanced sensor performance parameters for optimizing grating geometry have been explored in detail for visible and NIR wavelengths of 633 nm and 984 nm, respectively. These findings are important for developing of localized surface plasmon sensors with enhanced performance.

Keywords (OCIS):

  • (240.6680) Optics at surfaces : Surface plasmons
  • (280.4788) Remote sensing and sensors : Optical sensing and sensors
  • (050.6624) Diffraction and gratings : Subwavelength structures

Experimental study and analytical model of deformation of magnetostrictive films as applied to mirrors for X-ray space telescopes

  • Xiaoli Wang, Peter Knapp, S. Vaynman, M. Graham, Jian Cao, and M. Ulmer
  • received 05/12/2014; accepted 08/16/2014; posted 08/18/2014; Doc. ID 211875
  • [full text: PDF (886) KB)]
  • Abstract: The desire of continuously gaining new knowledge in Astronomy has pushed the frontier of engineering methods to deliver lighter, thinner, high quality mirrors at an affordable cost for use in an X-ray observatory. To address these needs, we have been investigating the application of magnetic smart materials (MSMs) deposited as a thin film on mirror substrates. MSMs have some interesting properties that make the application of MSMs to mirror substrates a promising solution for making the next generation of X-ray telescopes. Due to the ability to hold a shape with an impressed permanent magnetic field, MSMs have the potential to be the method used to make light weight, affordable X-ray telescope mirrors. This paper presents the experimental setup of measuring the deformation of the magnetostrictive bimorph specimens under an applied magnetic field, and the analytical and numerical analysis of the deformation. As a first step in the development of tools to predict deflections, we deposited Terfenol-DTM on the glass substrates. We then made measurements that were compared with the results from the analytical and numerical analysis. The surface profiles of thin-film specimens were measured under an external magnetic field with White Light Interferometry (WLI). The analytical model provides good predictions of film deformation behavior under various magnetic field strengths. This work establishes a solid foundation for further research to analyze the full three-dimensional deformation behavior of magnetostrictive thin films.

Keywords (OCIS):

  • (340.0340) X-ray optics : X-ray optics
  • (340.7470) X-ray optics : X-ray mirrors
  • (350.1260) Other areas of optics : Astronomical optics
  • (310.6845) Thin films : Thin film devices and applications
  • (220.1080) Optical design and fabrication : Active or adaptive optics

A method to remove the effect of ambient temperature on radiometric calibration

  • Songtao Chang, Yaoyu Zhang, Zhiyuan Sun, and Min Li
  • received 07/18/2014; accepted 08/15/2014; posted 08/18/2014; Doc. ID 217232
  • [full text: PDF (446) KB)]
  • Abstract: High precision radiometric calibration is essential for infrared imaging systems, especially in scientific applications where an accurate quantitative analysis is required. Nevertheless, calibration and radiometry are usually not simultaneously performed. Hence the discrepancy of ambient temperature between calibration and actual measurement can generate significant measurement errors unless the calibration results have been properly corrected. To overcome the restriction, we studied the effect of ambient temperature on radiometric calibration, then derived the relationship between calibration results and ambient temperature considering the integration time. A novel method compensating for the impact of ambient temperature on the calibration of a cooled infrared system is proposed. Several experiments are performed, and the results indicate that the proposed method can not only ensure the accuracy of calibration but achieve calibration results under any ambient temperature and arbitrary integration time.

Keywords (OCIS):

  • (040.2480) Detectors : FLIR, forward-looking infrared
  • (040.3060) Detectors : Infrared
  • (120.6810) Instrumentation, measurement, and metrology : Thermal effects
  • (290.2648) Scattering : Stray light
  • (010.5630) Atmospheric and oceanic optics : Radiometry

Propagation characteristics of a focused laser beam in a Strontium Barium Niobate photorefractive crystal under reverse external electric field

  • B. Liang, Q. Guo, Y. Wang, G. Deng, Y. Jiang, S. Zhang, G. Fu, and P. Simmonds
  • received 05/01/2014; accepted 08/15/2014; posted 08/26/2014; Doc. ID 211171
  • [full text: PDF (588) KB)]
  • Abstract: The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=Is/Ib) under reverse external electric field. In the range 20 > R > 0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03 > R > 0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to “enhancement”, not “screening” of the external electrical field.

Keywords (OCIS):

  • (160.5320) Materials : Photorefractive materials
  • (190.4400) Nonlinear optics : Nonlinear optics, materials
  • (190.5330) Nonlinear optics : Photorefractive optics
  • (190.6135) Nonlinear optics : Spatial solitons

Bandwidth optimization of femtosecond pure-rotational coherent anti-Stokes Raman scattering by pump/Stokes spectral focusing

  • Sean Kearney
  • received 07/10/2014; accepted 08/14/2014; posted 08/26/2014; Doc. ID 216703
  • [full text: PDF (683) KB)]
  • Abstract: A simple spectral focusing scheme for bandwidth optimization of gas-phase rotational coherent anti-Stokes Raman scattering (CARS) spectra is presented. The method is useful when femtosecond pump/Stokes preparation of the Raman coherence is utilized. The approach is of practical utility when working with laser pulses that are not strictly transform limited, or when windows or other sources of pulse chirp may be present in the experiment. A delay between the femtosecond preparation pulses is introduced to shift the maximum Raman preparation away from zero frequency and toward the Stokes or anti-Stokes side of the spectrum with no loss in total preparation bandwidth. Shifts of 100 cm−1 or more are attainable and allow for enhanced detection of high-energy (150-300 cm−1) rotational Raman transitions at near transform-limited optimum sensitivity. A simple theoretical treatment for the case of identical pump and Stokes pulses with linear frequency chirp is presented. The approach is then demonstrated experimentally for typical levels of transform-limited laser performance obtained our laboratory with nonresonant CARS in argon and Raman-resonant spectra from a lean H2/air flat flame.

Keywords (OCIS):

  • (120.1740) Instrumentation, measurement, and metrology : Combustion diagnostics
  • (190.1900) Nonlinear optics : Diagnostic applications of nonlinear optics
  • (190.4380) Nonlinear optics : Nonlinear optics, four-wave mixing
  • (300.6230) Spectroscopy : Spectroscopy, coherent anti-Stokes Raman scattering
  • (320.2250) Ultrafast optics : Femtosecond phenomena

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