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August


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

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

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

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

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

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

Reduction of moiré for coarse integral volumetric imaging

  • Shimpei Sawada, Yukio Ueda, and Hideki Kakeya
  • received 06/16/2014; accepted 08/14/2014; posted 08/18/2014; Doc. ID 213787
  • [full text: PDF (1856) KB)]
  • Abstract: This paper proposes two moiré reduction methods for coarse integral volumetric displays composed of multilayer display panels. The quality of the image presented by the conventional multilayer integral imaging stays relatively low because of the moiré pattern, which appears due to the layering structure of display panels with limited pixel aperture. The authors propose two methods to solve this problem. The first method is to add another layer of convex lens array with short focal length on the front side of the layered display panels. The second method is to enlarge the pixel pitch of the back layer panel while fixing that of the front layer panel.

Keywords (OCIS):

  • (080.2740) Geometric optics : Geometric optical design
  • (100.6890) Image processing : Three-dimensional image processing
  • (120.2040) Instrumentation, measurement, and metrology : Displays

Design and Simulation of a Nano-Scale Electro-Plasmonic 1×2 switch based on Asymmetric Metal-Insulator-Metal Stub filters

  • Ahmad Naseri Taheri and Hassan Kaatuzian
  • received 05/28/2014; accepted 08/14/2014; posted 08/27/2014; Doc. ID 213004
  • [full text: PDF (1007) KB)]
  • Abstract: A compact nano-scale electro-plasmonic 1×2 switch based on asymmetrical metal-insulator-metal stub filters is introduced. The structure is designed and analyzed based on the Transmission Line Method (TLM) and the switching operation of the device is numerically simulated and verified by the Finite Element Method (FEM). It is found that by adjusting the length of the stubs on each output branch of the structure the Surface Plasmon Polaritons (SPPs) are guided to only one of the output ports. By altering the refractive index of the Electro-Optical material (DAST) as the core of the structure with a 10V applied voltage, the SPPs are steered to the opposite port. The reflected SPPs from one stub filter enhance the output intensity of the reciprocal filter. The operating wavelength of the switch is the communication wavelength λ=1550nm. Nevertheless, it can be easily redesigned for another wavelength in the range of 800nm to 2000nm. The insertion losses and the extinction ratios guarantee an almost symmetrical switching for two outputs. The overall size of the switch is 400nm×450nm×600nm. The bandwidth of the switch is anticipated over 100GHz.

Keywords (OCIS):

  • (230.2090) Optical devices : Electro-optical devices
  • (130.4815) Integrated optics : Optical switching devices
  • (250.5403) Optoelectronics : Plasmonics

Injected Current Reshaping in Distance Measurement by Laser Self-Mixing Interferometry

  • Ke Kou, Xingfei Li, Li Li, and Hongbiao Xiang
  • received 06/25/2014; accepted 08/14/2014; posted 08/14/2014; Doc. ID 214486
  • [full text: PDF (419) KB)]
  • Abstract: Self-mixing interferometry (SMI), as an extreme simple and compact laser range finding technique, is especially appropriate to develop minitype sensors for narrow space and small precision parts. In order to enhance the distance resolution performance of this technique, we described the mechanism of nonlinearity in laser frequency under injected current tuning, and proposed a current reshaping method to linearize the laser frequency to attain higher resolution in the scheme of SMI. The proof of nonlinearity was obtained through numerical simulation by considering the change of temperature and carrier concentration and experiment by complex wavelet analysis. Current reshaping method, based on the experimental data of wavelength versus injected current, was proposed to suppress the nonlinearity and improve the distance resolution to better than 20 μm over the range of 2.4-20.4 cm. The influence of tuning parameters and other sources of error was discussed additionally.

Keywords (OCIS):

  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (120.3940) Instrumentation, measurement, and metrology : Metrology
  • (120.4630) Instrumentation, measurement, and metrology : Optical inspection
  • (280.3420) Remote sensing and sensors : Laser sensors
  • (140.3518) Lasers and laser optics : Lasers, frequency modulated

(LC2014) Photographic Observation and Optical Simulation of a Pollen Corona Display in Japan

  • Souichiro Hioki and Hironobu Iwabuchi
  • received 07/02/2014; accepted 08/14/2014; posted 08/15/2014; Doc. ID 215247
  • [full text: PDF (1187) KB)]
  • Abstract: Brightness and chromaticity profiles were extracted from a vivid solar corona image taken with a digital camera in Sendai, Japan, to compare with a radiative transfer simulation applying Lorenz–Mie theory and single-scattering approximation. The comparison revealed suspended particles having a narrow particle size distribution peaking at radius 14.5 μm. Presumably, pollen of an indigenous coniferous tree, the cryptomeria (Cryptomeria japonica), is responsible for the corona display. The extracted brightness and chromaticity profiles are reproduced well by assuming the presence of a water soluble aerosol and dust in addition to the pollen. We find that photographic analysis of corona displays, similar to that used to measure cloud particle size, is applicable to estimating pollen particle size distribution and column number density.

Keywords (OCIS):

  • (010.1110) Atmospheric and oceanic optics : Aerosols
  • (010.1290) Atmospheric and oceanic optics : Atmospheric optics
  • (010.1310) Atmospheric and oceanic optics : Atmospheric scattering
  • (010.1690) Atmospheric and oceanic optics : Color

An underwater blast wave pressure sensor based on polymer film fiber F-P cavity

  • Wang Junjie, Wang Meng, Xia Minghe, Xu Jian, Peng Li, Yang Minghong, and Jiang Desheng
  • received 11/04/2013; accepted 08/14/2014; posted 08/18/2014; Doc. ID 200516
  • [full text: PDF (729) KB)]
  • Abstract: This paper describes the theoretical and experimental aspects of an optical underwater shock wave sensor based on polymer film optical fiber F-P cavity manufactured by vacuum deposition technology. The transduction mechanism of the sensor involves a normally incident acoustic stress wave that changes the thickness of the polymer film, thereby giving rise to a phase shift. This transient interferometric phase is interrogated by a three-phase-step algorithm. Theoretically, the sensor-acoustic-field interaction principle is analyzed, and the phase modulation sensitivity based on theory of waves in the layered media is calculated. Experimentally, a static calibration test and a dynamic calibration test are conducted using a piston-type pressure calibration machine and a focusing type electromagnetic shock wave. Results indicate that the repeatability, hysteresis and nonlinearity of the sensor with the pressure under 55MPa are 1.816%, 1.729% and 1.814%, respectively. Therefore, the overall measurement accuracy is ±[1.816%+1.729%+1.814%)/2] ≈ ±3.409% within the full range, and the dynamic response time is less than 0.767 µs. Finally, the three aspects that need further study for practical use are pointed out.

Keywords (OCIS):

  • (060.2370) Fiber optics and optical communications : Fiber optics sensors
  • (120.0280) Instrumentation, measurement, and metrology : Remote sensing and sensors
  • (120.2230) Instrumentation, measurement, and metrology : Fabry-Perot
  • (120.3930) Instrumentation, measurement, and metrology : Metrological instrumentation
  • (120.4640) Instrumentation, measurement, and metrology : Optical instruments
  • (120.5475) Instrumentation, measurement, and metrology : Pressure measurement

Broadly wavelength tunable acoustic-optically Q-switched Tm:LSO laser

  • T. Feng, K. Yang, S. Zhao, J. Zhao, W. Qiao, T. Li, L. Zheng, and J. Xu
  • received 07/02/2014; accepted 08/13/2014; posted 08/14/2014; Doc. ID 215219
  • [full text: PDF (753) KB)]
  • Abstract: A broadly wavelength tunable acoustic-optically Q-switched Tm:LSO laser has been presented for the first time, to our best knowledge. The emission wavelength was tuned in a broad spectral region over 111 nm ranging from 1959 nm to 2070 nm. A shortest pulse duration of 345 ns with a beam quality of M2≤1.65 was obtained at pulse repetition frequency of 1 kHz, corresponding to a maximum single pulse energy of 0.26 mJ and peak power of 0.75 kW. The experimental results indicated the Tm:LSO crystal an outstanding potential of obtaining broadly wavelength tunable and low PRF laser pulses at 2 μm.

Keywords (OCIS):

  • (140.3460) Lasers and laser optics : Lasers
  • (140.3480) Lasers and laser optics : Lasers, diode-pumped
  • (140.3540) Lasers and laser optics : Lasers, Q-switched
  • (140.3600) Lasers and laser optics : Lasers, tunable

Resolution properties of transmission-mode exponential-doping Ga0.37Al0.63As photocathode

  • Honggang Wang, Xiaoqian Fu, Xuehong Ji, Yujie Du, Jian Liu, Yunsheng Qian, and Benkang Chang
  • received 05/30/2014; accepted 08/13/2014; posted 08/13/2014; Doc. ID 213158
  • [full text: PDF (600) KB)]
  • Abstract: Using the modulation transfer function obtained by establishing and solving the two-dimensional continuity equation, we have calculated and comparatively analyzed the resolution characteristics of transmission-mode exponential-doping and uniform-doping Ga0.37Al0.63As photocathodes. The calculations show that, compared with the uniform-doping Ga0.37Al0.63As photocathode, the exponential-doping structure can improve significantly not only the resolution but also the quantum efficiency of photocathode. This improvement is different from the approach for high resolution by reducing the emission layer thickness and the electron diffusion length or by increasing the recombination velocity of back-interface , which results in low quantum efficiency. Furthermore, the improvement of resolution and quantum efficiency for transmission-mode exponential-doping Ga0.37Al0.63As photocathode is the result of the effect of the built-in electric field on electrons transport and lateral diffusion.

Keywords (OCIS):

  • (040.3780) Detectors : Low light level
  • (160.6000) Materials : Semiconductor materials
  • (230.0250) Optical devices : Optoelectronics
  • (250.0040) Optoelectronics : Detectors

Two synchronized modes of ultrashort optical pulses in a two-beam pumped Ti:sapphire laser

  • Changjun Zhu, Guoqing Zhang, Bing Xue, and Xuejun Zhai
  • received 05/16/2014; accepted 08/13/2014; posted 08/14/2014; Doc. ID 212260
  • [full text: PDF (474) KB)]
  • Abstract: A two-beam-pumped dual-cavity Ti:sapphire laser in which femtosecond and picosecond laser pulses can be produced has been constructed. Two synchronized modes, femtosecond-femtosecond pulse synchronization and femtosecond-picosecond pulse synchronization, have been achieved, respectively. In the mode of femtosecond-femtosecond pulse synchronization, laser pulses of 26 fs and 23 fs were generated in the two laser cavities, respectively, with a timing jitter of 7 fs. In the mode of femtosecond-picosecond pulse synchronization, laser pulses of 29 fs and 1.49 ps were generated in the femtosecond and picosecond cavities, respectively, with a timing jitter of 30 fs. The results show that the operating stability and pulse synchronization are primarily governed by cross mode-locking which is induced by cross-phase modulation in the two laser cavities.

Keywords (OCIS):

  • (320.5550) Ultrafast optics : Pulses
  • (320.7080) Ultrafast optics : Ultrafast devices
  • (320.7090) Ultrafast optics : Ultrafast lasers
  • (320.7160) Ultrafast optics : Ultrafast technology

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