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Contents
2002
Volume: 29 Issue 10
22 Article(s)
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Research Article
Study on the Near-field Scanning Optical Microscopy Based on Self-consistent Theory
[in Chinese], [in Chinese], and [in Chinese]
In this paper, the probe sample interaction equations based on dipole self consistent theory are given, and the resolution of near field scanning optical microscopy is calculated numerically. The analysis results show that the light intensity received by the probe is the outcome of interference of light fields radiatedIn this paper, the probe sample interaction equations based on dipole self consistent theory are given, and the resolution of near field scanning optical microscopy is calculated numerically. The analysis results show that the light intensity received by the probe is the outcome of interference of light fields radiated by sample, and that the distance between probe and sample and the interference of light fields radiated by sample play the important roles for the resolution of NSOM..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 871 (2002)
Effect of Resonator Thermal Deformation on Focusing Characteristics in Flying Optics for a High Power CO2 Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
For a high power CO 2 laser, its work medium and resonator components including mirrors and coupler will be distorted under the condition of high power laser output. Although with various cooling methods for the resonator, the distortions always happen under different output powers. It means the Rayleigh range Z R ofFor a high power CO 2 laser, its work medium and resonator components including mirrors and coupler will be distorted under the condition of high power laser output. Although with various cooling methods for the resonator, the distortions always happen under different output powers. It means the Rayleigh range Z R of the certain resonator is varying under different output power. The change rule of Rayleigh range Z R of output beams caused by the output coupler thermal deformation at various output power are researched. An adaptive optics system, which can compensate the change of Rayleigh range Z R and revises the effect caused by the thermal distortion of the output coupler, was used. Good focusing characteristics in flying optics is achieved in this way..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 875 (2002)
Analysis and Simulation on Annealing of Long-period Fiber Grating inHydrogen-loaded Fiber
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Considered the refractive index changes caused by hydrogen molecular, this paper developed a simple model based on three layer step index waveguide and coupled mode theory to analyze and simulate the annealing of long period fiber grating inscribed in hydrogen loaded fiber. The results agree well with the experiments.Considered the refractive index changes caused by hydrogen molecular, this paper developed a simple model based on three layer step index waveguide and coupled mode theory to analyze and simulate the annealing of long period fiber grating inscribed in hydrogen loaded fiber. The results agree well with the experiments..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 911 (2002)
Influencing of Phase Mask Characteristic on Optical Fiber Grating (OFG) Performance
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In this article the influence of phase mask characteristic on OFG performance is introduced. The theory analysis and experiments show that the characteristic of the phase mask directly influence the power flatten coefficient and the time delay deviation (TDD) of the chirped OFG, then the TDD will influence dispersion eIn this article the influence of phase mask characteristic on OFG performance is introduced. The theory analysis and experiments show that the characteristic of the phase mask directly influence the power flatten coefficient and the time delay deviation (TDD) of the chirped OFG, then the TDD will influence dispersion effect of chirped OFG, so the parameters of the phase mask must be stricted. By choosing good quality phase mask and controlling the UV scan exposal course, the high quality OFG is fabricated which has the time delay deviation less than 20 ps and its reflectivity is flatness with ripple coefficient less than 1 dB..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 915 (2002)
Beam Transmission
Pattern Characteristics of Collimated Laser Beam in a Turbulent Atmosphere Ⅰ.Characteristic Radii
[in Chinese]
Besides the effective radius R eff , the robust radius R rbt and the sharpness radius R shp are introduced. The validity of three kinds of radii, two characteristic radii, for describing the pattern quality are test through numerically generated patterns of a collimated laser beam propagating through a turbulenBesides the effective radius R eff , the robust radius R rbt and the sharpness radius R shp are introduced. The validity of three kinds of radii, two characteristic radii, for describing the pattern quality are test through numerically generated patterns of a collimated laser beam propagating through a turbulent atmosphere, and main results could be summarized as follows. R rbt and R eff are equivalent for Gaussian beams, but the former can be used for more general patterns. Both of them are not valid for evaluating the pattern quality; and R shp can well used for the purpose. For laser beam patterns in the turbulence under very weak fluctuation condition, in a very limited extent, the pattern quality for half of them will be degraded, and for another half the quality will be refined. With increase of the fluctuation condition, the quality of more and more patterns will be degraded, and there still be some patterns whose quality will be refined in a deeper extent..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 889 (2002)
Laser Thermal Effects in Beam Control System on the Emitted Laser Quality
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The thermal effects, produced by the high energy laser in a beam control system, are numerically analyzed in this paper. The effects on the laser density and beam facula quality at far field are studied in particular. The propagation of laser is described by the paraxial wave equations, solved by the phase screen technThe thermal effects, produced by the high energy laser in a beam control system, are numerically analyzed in this paper. The effects on the laser density and beam facula quality at far field are studied in particular. The propagation of laser is described by the paraxial wave equations, solved by the phase screen technique and the FFT method. The thermal turbulence motion and the air density variation are governed by the complete Navier Stokes equations, so that the variety factors could be in consideration. The Navier Stokes equations are solved by using the LU SGS factorization technique. The numerical results show that, with the additional initial thermal phase at the emitter exit, the energy density and the quality of the laser beam at far field would be prominently degraded for the typical situations..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 895 (2002)
Holography and Information Processing
Adaptive Filter for Unwrapping Noisy Phase Image in Phase-stepping Interferometry
[in Chinese], [in Chinese], and [in Chinese]
An adaptive filter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median filter is adjustable according to its location in the noisy phase image. Phase unwrapping can then be done to recover the real phase image without the hampering influence of noise, especiaAn adaptive filter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median filter is adjustable according to its location in the noisy phase image. Phase unwrapping can then be done to recover the real phase image without the hampering influence of noise, especially the noise near the phase jumps. Both numerical simulation and experimental results used to examine the effectiveness of this adaptive filter are presented..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 929 (2002)
Study on Modulation-array Code Suitable for Digital Holographic Storage
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A modified coding structure, Modulation Array (MA) code, and a novel soft decision method corresponding to MA code are proposed for data processing in digital holographic storage systems. Also developed based on the MA code is a new iterative decoding algorithm, which integrates principles of modulation code detection,A modified coding structure, Modulation Array (MA) code, and a novel soft decision method corresponding to MA code are proposed for data processing in digital holographic storage systems. Also developed based on the MA code is a new iterative decoding algorithm, which integrates principles of modulation code detection, soft decision, array code error correction and Turbo code decoding. Experimental results show that when the signal to noise ratio in the channel is low and varying, and the noise parameters are difficult to calculate, this MA code can exploit the information contained in the input data effectively. As long as the raw bit error rate (BER), which is defined as the BER after global optimum threshold quantization, is around 4×10 -2 the output BER of the 8×10 MA code is equivalent to that of traditional 1∶2 modulation code (both codes have the similar code rate). For the raw BER lower than 1×10 -2 the MA code exhibits obvious advantage over the 1∶2 modulation code. Using these techniques, a preliminary experiment has been conducted to store and successfully replay multimedia data including video and audio information..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 935 (2002)
Rotating Invariance Matched Filtering Correlation Recognition Based on Inverse Filter
[in Chinese], [in Chinese], and [in Chinese]
Based on inverse filtering technique, a method of rotating invariance matched filtering correlation recognition is proposed in this paper. Using cascade modified filter method, the optimization of transmitted matched correlation peak intensity to transmitted input energy can be realized. And so the sharpness of correlaBased on inverse filtering technique, a method of rotating invariance matched filtering correlation recognition is proposed in this paper. Using cascade modified filter method, the optimization of transmitted matched correlation peak intensity to transmitted input energy can be realized. And so the sharpness of correlation peak is improved greatly. The computer simulation results show that for the rotating image, the rotating invariance matched filtering correlator of rotating 0°～32° with 4° interval proposed in this paper possesses good correlation invariance recognition performance, especially the target recognition can still be successfully in progress under the case of partly input target image..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 941 (2002)
Laser Manufacturing
Study on Laser Phase Transformation Hardening of HT250 by High Speed Axis Flow CO2 Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In this article, laser phase transformation hardening of HT250 material by high speed axis flow CO2 laser is investigated. Appropriate laser hardening parameters, such as laser power P (W),laser scanning rate V (m/min), have been optimized through a number of experiments. The effects of the parameters on the hardened zIn this article, laser phase transformation hardening of HT250 material by high speed axis flow CO2 laser is investigated. Appropriate laser hardening parameters, such as laser power P (W),laser scanning rate V (m/min), have been optimized through a number of experiments. The effects of the parameters on the hardened zone, including case depth, micro hardness distributions etc. are analyzed. The experiment shows that the axis flow CO 2 laser, which commonly outputs low mode laser beam, also can heat treat materials as long as the treating parameters used are rational. During the experiments, the surface qualities of the specimens treated with optimized parameters were enhanced, which incoincided with former results. According to the experimental results, the relation between the optimized parameters, the laser power densities q and the scanning rates V is given..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 945 (2002)
Smoke Particles' Recognition and Monte Carlo Simulation of Laser Scattering Characters
[in Chinese], [in Chinese], and [in Chinese]
Based on the particle laser scattering, the paper puts forward a smoke recognition system with multi sensor array. And then a Monte Carlo method is described to simulate the scattering characters of smoke particles. By changing the sizes, refractive index of the smoke particles and incident angles of light source, the Based on the particle laser scattering, the paper puts forward a smoke recognition system with multi sensor array. And then a Monte Carlo method is described to simulate the scattering characters of smoke particles. By changing the sizes, refractive index of the smoke particles and incident angles of light source, the simulation results fit well with the classical results derived from Mie scattering theory..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 950 (2002)
Research on the Laser Fiber-optic Pressure Measurement Technique for Offshore Oil Exploration
[in Chinese], and [in Chinese]
A novel reflex fiber optic pressure sensor used in the offshore oil exploration was proposed. Based on the original network compensation technique, the long term stability and the measurement accuracy of the intensity modulated fiber optic sensors were tremendously improved. The error compensation principle of the sensA novel reflex fiber optic pressure sensor used in the offshore oil exploration was proposed. Based on the original network compensation technique, the long term stability and the measurement accuracy of the intensity modulated fiber optic sensors were tremendously improved. The error compensation principle of the sensor was theoretically described. Preliminary experimental results indicated the feasibility and practicability, and the estimated pressure measurement accuracy will reach 0.1 MPa. The measurement stability can reach 0.15% when it was applied on the underground crude oil exploration..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 955 (2002)
Laser Physics
Study on the Self Mode-locking Yb-doped Fiber Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A stable ns pulse has been generated from a self mode locking Yb doped fiber laser using Yb doped fiber Bragg grating with 15 dB reflectivity as a reflector, and the pulse width is less than 5 ns. The average output power about 3 mW and repetition rate of 25 MHz are obtained under stable mode locking condition. The lasA stable ns pulse has been generated from a self mode locking Yb doped fiber laser using Yb doped fiber Bragg grating with 15 dB reflectivity as a reflector, and the pulse width is less than 5 ns. The average output power about 3 mW and repetition rate of 25 MHz are obtained under stable mode locking condition. The laser threshold is 18 mW and energy convert efficiency is 5%. The cause and characteristics of the self mode locking fiber laser have been also investigated..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 865 (2002)
Wavelength Changeable L-band Er-doped Fiber Laser Usinga High-birefringence Fiber Loop Mirror
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A linear cavity erbium doped fiber laser operating in L band, which utilizes amplified spontaneous emission (ASE) as a secondary pump source, is presented. The output wavelength can be changed from 1583 nm to 1600 nm by using a high birefringence fiber loop mirror as a wavelength filter and the stability of the output A linear cavity erbium doped fiber laser operating in L band, which utilizes amplified spontaneous emission (ASE) as a secondary pump source, is presented. The output wavelength can be changed from 1583 nm to 1600 nm by using a high birefringence fiber loop mirror as a wavelength filter and the stability of the output laser was very good..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 868 (2002)
Dissociation of the NaK (E) State and Branching Ratio of the Na(3PJ) Fine-structure Levels
[in Chinese], and [in Chinese]
The process studied is Na(3S)+K(4S)+nhν→Na(3PJ)+K(4S)+(n-1)hν, where the laser frequency ν is tuned in the wings of the Na resonance transition. The branching ratio is defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic NaD1 and D2 lines, respectively. The branching is determined in the The process studied is Na(3S)+K(4S)+nhν→Na(3PJ)+K(4S)+(n-1)hν, where the laser frequency ν is tuned in the wings of the Na resonance transition. The branching ratio is defined as I(D1)/I(D2) where I(D1) and I(D2) are measured intensities of the atomic NaD1 and D2 lines, respectively. The branching is determined in the K density range of 2～8×10 20 m-3 . The ratio is measured for detuning ranging from about 300 cm-1 in the blue wing to 100 cm -1 in the red wing of the Na3P multiplet. The ratio of dissociation rates and the fine structure changing cross section are obtained. The branching is found to be strongly detuning dependent in the vicinity of the NaK near wing satellites. Fine structure changing cross section has also been measured for resonant excitation of Na3P J state. The results are discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 879 (2002)
Theory and Simulation of Amplified Pulses from Chirped-pulse Laser Amplifier
[in Chinese], [in Chinese], and [in Chinese]
Using parameters of Nd∶glass and Ti∶sapphire, simulation to nonlinear SchrAo¨Gdinger equation about chirped pulse propagation was demonstrated by split step Fourier method, the effect of self phase modulation, gain narrowing and gain saturation to amplified chirped pulses was discussed, and distorted intensity pUsing parameters of Nd∶glass and Ti∶sapphire, simulation to nonlinear SchrAo¨Gdinger equation about chirped pulse propagation was demonstrated by split step Fourier method, the effect of self phase modulation, gain narrowing and gain saturation to amplified chirped pulses was discussed, and distorted intensity profiles of amplified pulses were also demonstrated here. Putting emphasis on the effect of self phase modulation and inter relationship between self phase and other two nonlinear effects, the analysis presented here is valid for high power laser amplifier designing..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 882 (2002)
Effect of Cubic Nonlinearity on Optical Parametric Amplification of Femtosecond Pulse at High Pumping Intensity
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The optical parametric amplification of femtosecond pulse at high pumping intensity is numerically simulated by computer.The effect of cubic nonlinearity on conversion efficient of the high intensity pump pulse and the envelopes of signal pulse are studied in detail. A suitable phase mismatch is introduced to compensatThe optical parametric amplification of femtosecond pulse at high pumping intensity is numerically simulated by computer.The effect of cubic nonlinearity on conversion efficient of the high intensity pump pulse and the envelopes of signal pulse are studied in detail. A suitable phase mismatch is introduced to compensate the nonlinear phase mismatch induced by cubic nonlinearity. The compensation can counteract the modulation on the signal pulse on count of cubic nonlinearity and prevent the energy converting from the signal back to pump in three wave interaction. So, higher optical conversion efficiency and better quality of amplificated signal can be gotten. An explicit explanation with cascaded nonlinear phase shift is presented..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 885 (2002)
Materials and Thin Films
Study of Laser Damage of Fused Silica and Sapphire Crystal
[in Chinese], [in Chinese], and [in Chinese]
The effect of different experiment conditions on the damage thresholds and damage morphologies of fused silica and sapphire are investigated. In addition, strengthened laser damage sterngth of fused silica is studied. Experimental results show that the laser damage thresholds of fused silica after laser pre irradiationThe effect of different experiment conditions on the damage thresholds and damage morphologies of fused silica and sapphire are investigated. In addition, strengthened laser damage sterngth of fused silica is studied. Experimental results show that the laser damage thresholds of fused silica after laser pre irradiation and acid etching treatment are increased by a factor of 70% and 80%, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 920 (2002)
Changes of Properties and Structure in Amorphous As2S3 Semiconductor Films Induced by Light Illumination
[in Chinese], and [in Chinese]
The optical absorption edges of amorphous As 2S 3 films shifted to lower energy with band gap light illumination or annealing near the glass transition temperature. The magnitude of red shift increased with the increase of the intensity of illumination light and the time of illumination and became saturated finally. ThThe optical absorption edges of amorphous As 2S 3 films shifted to lower energy with band gap light illumination or annealing near the glass transition temperature. The magnitude of red shift increased with the increase of the intensity of illumination light and the time of illumination and became saturated finally. The red shift in well annealed As 2S 3 film was reversible. Photocrystallization was also observed in the illuminated As 2S3 films with scanning electron microscope (SEM) measurements and the crystal phase was more with higher intensity of illumination light. The photoinduced effects in amorphous As 2S3 films were ascribed to photostructural changes and the change mechanisms are discussed in this paper..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 925 (2002)
Optical Communication
Impacts of Polarization Mode Dispersion on the Pulse Width in Linear Systems
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The impacts of polarization mode dispersion (PMD) on the pulse width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp, are derived. The results show that the broadening effects induced by the first order PMD are independent on group velocity dispersionThe impacts of polarization mode dispersion (PMD) on the pulse width in linear systems have been investigated. The analytical solutions, including the effects of initial frequency chirp, are derived. The results show that the broadening effects induced by the first order PMD are independent on group velocity dispersion (GVD) and chirp, which are different from the effects induced by the second order PMD. An initially chirped Gaussian pulse is taken as an example. Analytical solutions of rms pulse width are obtained before and after first order PMD compensation. It is shown that the broadening effects will be suppressed effectively by appropriately choosing GVD and chirp parameter; the post transmission compensation method will be less efficient than the PSP transmission method due to chirp..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 900 (2002)
L-band Er3+-doped Fiber Amplifier Based on Backward ASE
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
3 dB bandwidths of 56.3 nm and 47.6 nm of ASE spectra have been respectively obtained by using backward ASE pumping an unpumped EDF and a weak pumped EDF. The gain is 3.5 dB and 9.2 dB for a small input signal of 1575 nm, respectively.3 dB bandwidths of 56.3 nm and 47.6 nm of ASE spectra have been respectively obtained by using backward ASE pumping an unpumped EDF and a weak pumped EDF. The gain is 3.5 dB and 9.2 dB for a small input signal of 1575 nm, respectively..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 905 (2002)
Experimental Study on the Tunable RCE Photodetectors with Built-in Liquid-crystal Layer
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
An experiment on the tunable RCE photodetectors with built in liquid crystal layer is reported. A tuning range of 8nm has been obtained. Corresponding theoretical analysis and discussions are presented.An experiment on the tunable RCE photodetectors with built in liquid crystal layer is reported. A tuning range of 8nm has been obtained. Corresponding theoretical analysis and discussions are presented..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 29, Issue 10, 908 (2002)
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