Journals >Chinese Journal of Lasers
Contents
2007
Volume: 34 Issue 11
26 Article(s)
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Research Article
Pulsed Dye Laser Amplifier with 50 W Output Power
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The principle and method of designing double-side transversely-pumped high-power pulsed dye laser amplifier are presented based on the simplified rate equation of transversely-pumped dye laser amplifier at quasi-steady state. A double-side transversely pumped dye laser amplifier with 50 W output power was developed basThe principle and method of designing double-side transversely-pumped high-power pulsed dye laser amplifier are presented based on the simplified rate equation of transversely-pumped dye laser amplifier at quasi-steady state. A double-side transversely pumped dye laser amplifier with 50 W output power was developed based on the results of physical design of high power pulsed dye laser amplifier. The experimental study has been performed on this dye laser amplifier pumped by copper vapor laser (CVL). The output power of the amplifier was over 52 W, and the extraction efficiency was up to 41%. The experimental results of the extraction efficiency and output power related to the laser wavelength, input dye laser power and pump beam′s temporal and spatial performance have been given. Furthermore, the influence of dye solution concentration on the beam quality of the double-side transversely-pumped dye laser amplifier has been discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1466 (2007)
High Brightness Operation of Fiber Coupling Multiplex Diode Lasers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A high brightness fiber coupling laser module with multiplex diode lasers (LDs) has been designed and fabricated. The diode laser chips has been fabricated with AlGaAs/GaAs material with broad waveguide and double quantum wells structure by molecular beam epitaxy (MBE), and the module contains 4 collimated single broadA high brightness fiber coupling laser module with multiplex diode lasers (LDs) has been designed and fabricated. The diode laser chips has been fabricated with AlGaAs/GaAs material with broad waveguide and double quantum wells structure by molecular beam epitaxy (MBE), and the module contains 4 collimated single broad area stripe diode lasers which can reach to continuous wave (CW) 5 W output power with emission width of 100 μm and cavity length of 2 mm. Output combination with high beam quality has been obtained by first space beam combination of each two devices and consequent polarization beam combination,and the combined four-beam output has been coupled into a 100 μm-core quartz fiber with numerical aperture (NA) 0.22 by a simple flat-convex lens. Finally, a 10.17 W output power from the fiber with a high power density of 1.0×105 W/cm2 is achieved, and the total coupling efficiency is as high as 79%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1472 (2007)
Transient Thermal Effect in Pulsed Laser Diode End-Pumped Solid-State Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Based on the fundamental theory of heat transfer in cylinder, the transient temperature field in the laser crystal of pulsed laser diode (LD) end-pumped Nd∶YAG laser is analyzed by the finite-element method. The temperature distribution of crystal end surface in the process of temperature rise and fall is calculated inBased on the fundamental theory of heat transfer in cylinder, the transient temperature field in the laser crystal of pulsed laser diode (LD) end-pumped Nd∶YAG laser is analyzed by the finite-element method. The temperature distribution of crystal end surface in the process of temperature rise and fall is calculated in a single pulse process. The influences of beam waist width and its location on the temperature distribution and the factors influencing the thermal relaxation time are presented. Based on the theory of ray trace, the time variation of optical path difference at the center and fringe of crystal end surface caused by temperature gradient after the temperature distribution in the crystal reaches a dynamic balance is analyzed. The results show that the increase of beam waist width or rearward shift the beam waist without changing beam waist width will reduce the end surface temperature when the laser beam waist is located on the pumped end surface. Increasing the heat transfer coefficient of cooling liquid or flow velocity of air, reducing the air temperature or the radius of laser crystal can shorten the thermal relaxation time. After the transient temperature distribution reach a dynamic balance, the temperature in crystal and relative optical path difference (OPD) caused by radial temperature gradient will periodically change with time..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1476 (2007)
Thermal-Induced Birefringence-Compensated Laser System with Two Nd∶YAG Rods
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The thermal-induced birefringence is a key factor limiting the output power of a laser system in fundamental mode. Birefringence compensation is mandatory for high power lasers with good beam quality. The principle of birefringence compensation by use of two Nd∶YAG rods is investigated. Considering the thickness of a qThe thermal-induced birefringence is a key factor limiting the output power of a laser system in fundamental mode. Birefringence compensation is mandatory for high power lasers with good beam quality. The principle of birefringence compensation by use of two Nd∶YAG rods is investigated. Considering the thickness of a quartz polarization rotator, a revised model is presented by use of proper cavity structure and components with a 4f imaging spatial filter for birefringence compensation. The depolarization ratio less than 2.5% is achieved experimentally. By means of matrix optics, a cavity containing a two-rod system is equivalent to a thin lens, which allows one to analyze the system properties such as stability of the resonator and beam radius in the cavity. A positive lens is inserted into the cavity to enlarge the fundamental mode volume, 61W linearly polarized output is obtained in a lamp continuous wave (CW)-pumped Nd∶YAG laser. It is shown that the birefringence compensation is essential for a dynamic stable resonator with a lage fundamental mode volume..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1483 (2007)
High Efficiency 23.6 W, 2 μm Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A high-repetition-rate high-efficiency 2 μm laser was demonstrated. The tuning curve of the type Ⅱ phase matching KTP crystal pumped by 1.064 μm laser was calculated and it shows that when cut at φ=0°, θ=54°, a KTP optical parametric oscillator (OPO) gets output at near degenerated wavelength at 2 μm. The pumA high-repetition-rate high-efficiency 2 μm laser was demonstrated. The tuning curve of the type Ⅱ phase matching KTP crystal pumped by 1.064 μm laser was calculated and it shows that when cut at φ=0°, θ=54°, a KTP optical parametric oscillator (OPO) gets output at near degenerated wavelength at 2 μm. The pump source was 1.064 μm Nd∶YAG module. Walk-off compensation was realized by two short crystals in intracavity doubly resonant optical parametric oscillator (DROPO) and the average power of 23.6 W at 2.12 μm is obtained. The pulse repetition frequency of acoustic-optic Q-switch was 7 kHz and the slope efficiency of 808 nm laser diode (LD) to 2 μm laser was higher than 19%..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1488 (2007)
Passive Mode-Locking in Nd∶YAG Laser Using Nanocrystalline Silicon Embedded in SiNxFilm
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The nanocrystalline silicon embedded in SiNx (nc-Si-SiNx) film was prepared by radio-frequency (RF) magnetron sputtering technique and thermal annealing. The film of 200 nm thick was deposited on silica glass slice. The average diameter of nanocrystalline silicon in the film annealed at 800 ℃ for three hours was about The nanocrystalline silicon embedded in SiNx (nc-Si-SiNx) film was prepared by radio-frequency (RF) magnetron sputtering technique and thermal annealing. The film of 200 nm thick was deposited on silica glass slice. The average diameter of nanocrystalline silicon in the film annealed at 800 ℃ for three hours was about 1.7 nm according to X-ray diffraction (XRD) spectrum. The passive mode-locking operation of a flash-lamp pumped Nd∶YAG laser was achieved by inserting the nc-Si-SiNx film as the saturable absorber into the plane-concave resonator. A single pulse train with average pulse duration of 32 ps and energy of 25 mJ was obtained when the cavity length was 120 cm. The sustained time of a single pulse train was about 480 ns and the modulation depth of mode-locking was nearly 100%. The nc-Si-SiNx film passive mode-locking at 1.06 μm laser was mainly ascribed to two-photon saturable absorption and fast energy relaxation processes of carriers excited by laser in the nanocrystalline silicon since the energy band gap of the nanocrystalline silicon affected by the quantum confinement related effects was larger than the photon energy of 1.06 μm laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1498 (2007)
Multi-Wavelength Fiber Ring Laser with Semiconductor Optical Amplifier
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A semiconductor optical amplifier (SOA) multi-wavelength fiber ring laser with a Mach-Zehnder (M-Z) fiber interferometer was reported and stable multi-wavelength continuous-wave lasing oscillations with channel spacing of 100 GHz are achieved with the 3 dB spectral bandwidth of 19.5 nm and signal-to-noise ratio higher A semiconductor optical amplifier (SOA) multi-wavelength fiber ring laser with a Mach-Zehnder (M-Z) fiber interferometer was reported and stable multi-wavelength continuous-wave lasing oscillations with channel spacing of 100 GHz are achieved with the 3 dB spectral bandwidth of 19.5 nm and signal-to-noise ratio higher than 30 dB. It is observed that the output power variation of the 22 wavelengths in 17.9 nm is 1.2 dB and total output power is 5.1 dBm. The wide spectrum and low output power variation acquired in this laser are attributed to the self-averaging of multi-wavelength optical power induced by gain saturation and four-wave mixing ( FWM ) in SOA under the low cavity loss condition. The decrease of the spectral bandwidth and center wavelength with the decrease of driving current of SOA or the increase of cavity loss observed in the experiment was also discussed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1502 (2007)
Lumped Fiber Nonlinear Noise Compensation Based on Volterra Theory
[in Chinese], [in Chinese], and [in Chinese]
The semi-analytical solution of nonlinear Schrdinger equation (NLSE) is obtained by Volterra series theory, and the semi-analytical expression of coupling crosstalk between the useful pulses and amplified spontaneous emission (ASE) induced by the combined effects of fiber loss, dispersions and nonlinearities is derivedThe semi-analytical solution of nonlinear Schrdinger equation (NLSE) is obtained by Volterra series theory, and the semi-analytical expression of coupling crosstalk between the useful pulses and amplified spontaneous emission (ASE) induced by the combined effects of fiber loss, dispersions and nonlinearities is derived in a high-speed long-haul fiber-optic system, which is made up of multi-span with each including a transmission fiber and an erbium doped fiber amplifier (EDFA), and the relational expression between the output signal at the receiver and the input signal at the transmitter of multi-span transmission is also obtained. Besed on the time-domain filtering method of Wiener filtering, a Wiener filter is designed at the receiver to filter the multiplicative crosstalk noise mentioned above. Its applications in pre-, post-lumped and distributed dispersion compensation system, as well as “one-for-three” compensation fiber spans transmission lines with scaled translational symmetry are proved feasible by numerical simulations, which provide a novel solution to improve fiber input power and nonlinear channel capacity..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1527 (2007)
Beam Transmission
Modification of Aberration Nondiffraction Beams in Manufacture Error of Elliptical Axicon
[in Chinese], [in Chinese], and [in Chinese]
Beam′s oblique incidence and manufacture error of an axicon have a great influence on the quality of zero-order Bessel beams. Generally, the manufacture error is that the cross section of the axicon is not a circle but an ellipse. Based on the diffraction and geometry optics, the quality equivalence between the beam′s Beam′s oblique incidence and manufacture error of an axicon have a great influence on the quality of zero-order Bessel beams. Generally, the manufacture error is that the cross section of the axicon is not a circle but an ellipse. Based on the diffraction and geometry optics, the quality equivalence between the beam′s oblique incidence in a circular axicon and beams incidence in vertical angle in an elliptical axicon are analyzed. The diffractive optical patterns in oblique illumination on a circular axicon and the manufacture error in an elliptical axicon were simulated according to the calculation. The method to modify the influence on the nondiffraction Bessel beam of an elliptical axicon by rotating the axicon is proposed and the approximately perfect Bessel beams are obtained. The experimental result agrees with the theoretical analysis and numerical simulation..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1538 (2007)
Biomedical Photonics and Laser Medicine
Repair Effects and Damage of Cell of Wheat Seedlings Exposed to Enhanced Ultraviolet-B Radiation by He-Ne Laser
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The seedlings of wheat (Jinmai 8) were exposed to He-Ne laser with 5 mW·mm-2 power density, enhanced ultraviolet-B radiation (UV-B) (10.08 kJ·m-2·d-1) and the combination of He-Ne laser and enhanced UV-B radiation respectively for 5 days. Changes about production rate of superoxide anion, malondialdehydeThe seedlings of wheat (Jinmai 8) were exposed to He-Ne laser with 5 mW·mm-2 power density, enhanced ultraviolet-B radiation (UV-B) (10.08 kJ·m-2·d-1) and the combination of He-Ne laser and enhanced UV-B radiation respectively for 5 days. Changes about production rate of superoxide anion, malondialdehyde (MDA) content, ultraviolet absorption value and conductance of exosmic fluid of wheat seedlings, content of soluble protein and chlorophyll were measured to analyze the repair role of He-Ne laser irradiation. The results showed that He-Ne laser irradiation on the wheat seedlings led to the decrease of the production rate of superoxide anion, MDA content and ultraviolet absorption value and conductance of exosmic fluid of wheat seedlings. The content of soluble protein and chlorophyll increased to 76.66% and 1.79 mg/g respectively. It suggested that those changes about production rate of superoxide anion, MDA, ultraviolet absorbing value and conductance, soluble protein and chlorophyll were related to the repair capacity of the wheat seedings. Therefore, the damage of wheat seedlings induced by enhanced UV-B radiation can be repaired partly by He-Ne laser..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1594 (2007)
Holography and Information Processing
Shrinkage of Photopolymer for Holographic Recording Materials
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
An explicit relation between the Bragg shift of the grating readout angle and the shrinkage of photopolymer samples is presented based on the changes in amplitude and direction of the grating vector, caused by lateral shrinkage and thickness shrinkage of photopolymer after exposure. A two-step experimental method to meAn explicit relation between the Bragg shift of the grating readout angle and the shrinkage of photopolymer samples is presented based on the changes in amplitude and direction of the grating vector, caused by lateral shrinkage and thickness shrinkage of photopolymer after exposure. A two-step experimental method to measure the Bragg shift of the unslanted grating and slant grating in photo polymer separately is designed and implemented with blue light readin and red light readout. The lateral shrinkage and thickness shrinkage of two self-made blue-light photopolymer samples are calculated respectively, and their volume shrinkage are obtained. The results show that the volume shrinkage of the sample with modified composition is less than 0.5%. This study also shows that the lateral shrinkage of photopolymer is generally not negligible. By using this method, it is easier to measure the shrinkage of a large amount of photopolymer samples, and find the relation between shrinkage and compositions of photopolymer..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1543 (2007)
Laser Manufacturing
Laser Penetration Brazing of Brass and Low Carbon Steel
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A continuous wave (CW) Nd∶YAG laser with a output power of 1 kW was used to join H62 brass and 20# low carbon steel with a thickness of 2 mm. The focused laser beam with a diameter of 0.3 mm was irradiated at the brass side of the butt joint. Thus the brass was penetratingly melted and interacted with the solid steel tA continuous wave (CW) Nd∶YAG laser with a output power of 1 kW was used to join H62 brass and 20# low carbon steel with a thickness of 2 mm. The focused laser beam with a diameter of 0.3 mm was irradiated at the brass side of the butt joint. Thus the brass was penetratingly melted and interacted with the solid steel to form a brazing joint. The brass is penetratingly welded, and the low carbon steel is brazed. This process is called laser penetration brazing (LPB). The interfacial characterizations of the joint were investigated by metallographic microscope, scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS). The results show that the element diffusion and solution occur and metallurgical bonding is achieved between brass and steel. The width of the interaction layer is about 3μm. The brass weld is harder than that brass substrate and the failure occurs at the brass substrate but weld judged from the data of bursting test. The mechanic performance of H62 brass and 20# low carbon steel butt joint by laser penetration brazing can meet the demand of industrial application..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1562 (2007)
Microheater Array Fabrication by Laser Micro-Cladding Method
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The 2×2 and 1×4 microheater arrays have been fabricated by laser micro-cladding. The effect of laser power and scanning speed on the line width have been studied. The results demonstrate that the line width increases with the increase of laser power, and decreases with the increase of laser scanning speed. ThThe 2×2 and 1×4 microheater arrays have been fabricated by laser micro-cladding. The effect of laser power and scanning speed on the line width have been studied. The results demonstrate that the line width increases with the increase of laser power, and decreases with the increase of laser scanning speed. The performances of the 2×2 microheater array were tested. The effect of heating time, voltage and position on the temperature were studied. The results demonstrate that the temperature of the microheater increases with the increase of heating time and becomes unchangeable in the end. The temperature of the microheater increases with the increase of voltage. The temperature the heated area decreases with the increase of the distance to the microheater. And the calefactive speed was calculated when the voltage was stable, and it is up to 0.45 ℃/s. Lastly, some examples for microheaters array were demonstrated..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1567 (2007)
Cylinder Welding Control Technology of Integrated Laser Manufacturing System
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
To solve the difficulties in laser welding cylinder, laser system, robot system and rotary machine system are controlled synchronously by means of PROFIBUS-DP field-bus, GALIL movement controller card and COMM techniques. A novel method of multifunctional control laser welding for integrated laser manufacturing systemsTo solve the difficulties in laser welding cylinder, laser system, robot system and rotary machine system are controlled synchronously by means of PROFIBUS-DP field-bus, GALIL movement controller card and COMM techniques. A novel method of multifunctional control laser welding for integrated laser manufacturing systems is presented. Experiments based on this method were carried out and the results proved that the multifunctional control laser welding could meet the demands of practical applications, such as speed changing, power changing and angle deflexion. And problems of laser welding cylinder, such as welding instability and pits appeared at the end of welding, were solved. Programming is realized by VC++ object-oriented tools..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1571 (2007)
Model of One-Dimensional Thermal Stress Applied in Paint Removal by Q-Switched Short Pulse Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The thermal stress model was put forward in the paint removal from substrate by Q-switched laser pulses. With the one-dimensional equation of heat conduction, the thermal stress generated by thermal expansion was calculated. The adhesion force between the paint and the substrate was calculated according to adhesion forThe thermal stress model was put forward in the paint removal from substrate by Q-switched laser pulses. With the one-dimensional equation of heat conduction, the thermal stress generated by thermal expansion was calculated. The adhesion force between the paint and the substrate was calculated according to adhesion formula. If the thermal stress is greater than the adhesion force, the paint will be removed from the substrate by the laser action. When the Nd∶YAG laser with wavelength of 1064 nm and pulse width of 10 ns is used to remove orange paint from Fe substrate, the cleaning threshold is 0.5 J/cm2 and the irradiation time required for paint removal and the temperature change of Fe substrate were calculated according to the theoretical model. The experimental cleaning threshold is 0.57 J/cm2, which is in accordance with the theoretical result. From the experiments and theoretical model it is found that if the laser fluence is too high, the temperature of Fe substrate will exceed the melting point of Fe and the Fe substrate will be broken. And the paint removal on Al substrate by laser was taken into account..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1577 (2007)
Preparation of Silver Nanoparticles Colloid by Pulsed Laser Ablation
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Silver nanoparticles colloid was prepared by pulsed laser ablation of silver target for 10 min in distilled water at different repetition rate and laser fluence to study the effect of laser ablation parameters on the silver nanoparticles colloid. Particles size, morphology and absorption spectroscopy of the obtained naSilver nanoparticles colloid was prepared by pulsed laser ablation of silver target for 10 min in distilled water at different repetition rate and laser fluence to study the effect of laser ablation parameters on the silver nanoparticles colloid. Particles size, morphology and absorption spectroscopy of the obtained nanoparticles colloid were characterized by ultraviolet to visible (UV-Vis) spectrophotometer and transmission electron microscope (TEM), and the average diameter and diameter distribution were analyzed by Image-ProPlus software. The results showed that the average diameter of the silver nanoparticles prepared at repetition rate of 10 Hz and laser fluence of 4.2 J/cm2 was the smallest (D=17.54 nm), the distribution of particle size was narrowest (δ=36.86 nm) and the morphologies were fairly homogeneous. So it was confirmed that control of nanoparticles size and shape was possible by laser ablation parameters. In addition, based on the experimental results, the effects of laser ablation parameters on the silver nanoparticles colloid was discussed in terms of fragmentation and melting induced aggregation of colloidal particles by self-absorption of laser pulses..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1582 (2007)
Analysis of Silicon Surface Profile of Pulsed Laser Bending Processing
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Surface properties such as profile and crystal phase of bent silicon samples by long laser pulses were analyzed. The results indicated that the irradiated surface was divided into ambient region, transition region and main function region. The surfaces of the transition region and main function region were changed seriSurface properties such as profile and crystal phase of bent silicon samples by long laser pulses were analyzed. The results indicated that the irradiated surface was divided into ambient region, transition region and main function region. The surfaces of the transition region and main function region were changed seriously, and massing stacking fault and ripple profile were found respectively. The typical transformation of amorphous silicon was not found at Raman spectrum of the main function region, and only existed tiny Si-Ⅰ→Si-Ⅲ conversion. Meanwhile the crystal-plane orientation was changed seriously compared to the initial crystal-plane by X-ray crystal-plane identification, and crystal distortion and thinning appeared in the region irradiated..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1589 (2007)
Laser Physics
Numerical Simulation of Thermodynamics in Cooling for Heat Capacity Laser
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
The thermodynamic model of laser medium was established to study the thermodynamic characteristic in laser medium cooling of heat capacity laser. The exchange heat on the end surface of laser medium was regarded as the heat source of the transient heat conduction equation. The heat conduction model in cooling was got. The thermodynamic model of laser medium was established to study the thermodynamic characteristic in laser medium cooling of heat capacity laser. The exchange heat on the end surface of laser medium was regarded as the heat source of the transient heat conduction equation. The heat conduction model in cooling was got. The transient temperature field in the laser medium cooling was got. Then, the thermal stress of the laser medium was got. By using numerical simulation, the cooling time, and the different in temperature and thermal stress of the YAG medium and the GGG medium at different cooling condition were obtained. The cooling time is greatly decreased as the convective heat transfer coefficient is increased from 0.1 W·cm-2·K-1 to 0.5 W·cm-2·K-1. The cooling time is little decreased as the convective heat transfer coefficient increased from 0.5 W·cm-2·K-1 to 1 W·cm-2·K-1. The cooling time of YAG medium is less than that of GGG medium at the same volume and the same initial temperture field. The difference in temperatue and the maximal equivalent stress of YAG medium are less than that of GGG medium′ at the same cooling condition..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1507 (2007)
Ultra-Short Pulses Self-Similar Evolution Conditions in Normal Dispersive Fiber Amplifiers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Ultrashort pulses can evolve into self-similar parabolic pulses with a linear chirp in optical fiber amplifiers with normal group velocity dispersion, and the evolution result can affect the consequent pulse compression. The influences of the initial pulse width and energy as well as fiber dispersion and gain coefficieUltrashort pulses can evolve into self-similar parabolic pulses with a linear chirp in optical fiber amplifiers with normal group velocity dispersion, and the evolution result can affect the consequent pulse compression. The influences of the initial pulse width and energy as well as fiber dispersion and gain coefficient on the pulse self-similar evolution were numerically studied by split-step Fourier method, and the results reveal that dispersion length is the key factor determining whether the pulse can evolve self-similarly or not. When the dispersion length is close to fiber length (just severalfold), the initial pulse can evolve into a parabolic pulse; the larger the difference between the dispersion length and fiber length, the worse the self-similar evolution. Increasing the initial pulse energy can accelerate the pulse self-similar evolution, and therefore decrease the distance for self-similar evolution. Under a given amplifier total gain the higher the gain coefficient is, for the effect of nonlinear distortion, the worse the self-similar evolution is. When the gain coefficient is 0.95 m-1, the total gain of the amplifier is 3.3 dB larger than that when the gain coefficient is 3.8 m-1..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1512 (2007)
Materials and Thin Films
Deposition Rate′s Effects on Properties of LaF3Films Prepared by Thermal Boat Evaporation
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
LaF3 single-layer coatings were prepared by thermal boat evaporation at different deposition rates. Some of these films were annealed in vacuum. X-ray diffraction (XRD), Lambda 900 spectrophotometer and 355 nm Nd∶YAG laser system were employed to measure crystal structure, transmittance spectra and laser-induced damageLaF3 single-layer coatings were prepared by thermal boat evaporation at different deposition rates. Some of these films were annealed in vacuum. X-ray diffraction (XRD), Lambda 900 spectrophotometer and 355 nm Nd∶YAG laser system were employed to measure crystal structure, transmittance spectra and laser-induced damage threshold (LIDT) of the samples. Moreover, refractive index and extinction coefficient were obtained from the measured transmittance spectra. The results show that the crystallization and the preferential growth are benefited from the increase of the deposition rate, moreover, the refractive index is increased and the film gets more compact. But the defect makes the LIDT of the coating decline. In the other hand, the crystallization status will worsen if the deposition rate is too high. Meanwhile, a lot of pores appear in the film and the mechanical intensity of the film is deteriorated. Consequently, the refractive index and the LIDT are decreased. The LIDTs of the films after annealing are increased with different degree..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1557 (2007)
Measurement and Metrology
Image Mosaic Technique Based on Pseudo-Zernike Moments of Interest Points
[in Chinese], and [in Chinese]
The traditional feature-based algorithm was found to be sensitive to rotations and noise, and an automatic image mosaic technique based on pseudo-Zernike moments of interest points was proposed. Firstly the Harris corner detector was used to gain the interest points, and the pseudo-Zernike moments defined on the intereThe traditional feature-based algorithm was found to be sensitive to rotations and noise, and an automatic image mosaic technique based on pseudo-Zernike moments of interest points was proposed. Firstly the Harris corner detector was used to gain the interest points, and the pseudo-Zernike moments defined on the interest point neighborhood were computed. Through comparing the Euclidean distance of these pseudo-Zernike moments to extract the initial feature points pair, the spurious feature points pair were rejected by geometric transform model. After the geometric transform of input images, the overlapping region of two images was fused and the image stitching was finished. Experimental results demonstrate that the proposed algorithm is robust to translation, rotation, noise and slight scaling (under 1.5)..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1548 (2007)
Fast Axis Calibration of Quarter-Wave Plate by Foundamental Component Extinction
[in Chinese], [in Chinese], [in Chinese], and [in Chinese]
A method to calibrate the fast axis of a quarter-wave plate by nulling the foundamental component was proposed and the calibration principle was analyzed. The optical calibration system is composed of a laser, a polarizer, the quarter-wave plate to be calibrated, a phase modulator, an analyzer and an opto-electronic deA method to calibrate the fast axis of a quarter-wave plate by nulling the foundamental component was proposed and the calibration principle was analyzed. The optical calibration system is composed of a laser, a polarizer, the quarter-wave plate to be calibrated, a phase modulator, an analyzer and an opto-electronic detector. The azimuths of the transmission axes of the polarizer and the analyzer with respect to the major oscillation direction of the phase modulator are +45° and 0°, respectively. A collimated laser beam passes through the polarizer, the phase modulator, the quarter-wave plate and the analyzer in turn, and then is detected by the opto-electronic detector. The theoretical analyse shows that the calibration precision depends on the azimuth error of the analyzer. The feasibility of the method was verified by experiments. The maximum deviation of the calibrated fast axis azimuth of the quarter-wave plate is 0.043°, the root-mean-square error is 0.012°, and the calibration precision is 0.05°..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1553 (2007)
Optical Communication
Improvement for All-Optical Logical AND Gate Based on Cascaded Semiconductor Optical Amplifiers
[in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
In the all-optical logical AND gate based on cascaded two-stage semiconductor optical amplifiers (SOAs), the output signal from the first stage has notable impact on the final result. When the bulk material SOA with a slow carrier-recovery process is used in the first-stage conversion, the conversion speed beyond 10 GiIn the all-optical logical AND gate based on cascaded two-stage semiconductor optical amplifiers (SOAs), the output signal from the first stage has notable impact on the final result. When the bulk material SOA with a slow carrier-recovery process is used in the first-stage conversion, the conversion speed beyond 10 Gibt/s can not be reached perfectly, so the speed of all-optical logical AND operation is limited. The first-stage output signal will be improved when a delayed interferometer (DI) is cascaded after the first-stage SOA, and the second-stage all-optical logical AND gate operation will also benefit from the DI cascade. The function of the DI in the revised scheme is illustrated and simulated. In experiments, inverted-signals of high-speed return-to-zero (RZ) signals and non return-to-zero (NRZ) signals are realized by the modified scheme, so a high-speed all-optical logical AND gate is achieved. All-optical logical AND gate operation at 20 Gbit/s for pseudo-random RZ signals and NRZ signals is demonstrated experimentally, and the results at 40 Gbit/s are also analyzed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1517 (2007)
Fiber Bragg Grating Based Time Phase En-Decoder with Multiple Wavelength Channels
[in Chinese], [in Chinese], and [in Chinese]
Optical code-division multi-access (OCDMA) is one of the most attractive techniques to realize all optical access network. A new OCDMA en-decoder based on super structure fiber Bragg grating (SSFBG) is proposed. Based on the equivalent phase shift theory, the proposed en-decoder adopts Sinc function as its sampling funOptical code-division multi-access (OCDMA) is one of the most attractive techniques to realize all optical access network. A new OCDMA en-decoder based on super structure fiber Bragg grating (SSFBG) is proposed. Based on the equivalent phase shift theory, the proposed en-decoder adopts Sinc function as its sampling function and needs only one phase mask plate to achieve multiple en-decoding channels with similar performance. Users with different wavelength channels can be encoded (decoded) simultaneously by the proposed multi-channel en-decoder, and the capacity and compatibility of the system with wavelength division multiple (WDM) are improved. Analysis and computer simulation are made on the structure and performance of the encoder-decoder. Result shows that each channel achieves equivalent performance with the pure phase-shift en-decoder, the auto correlative P/W rates of each channel is more than 16.3 dB, the fluctuation of P/W rates is less than 0.4 dB, and the fluctuation of auto-correlation peak is less than 0.04 for the endecoder of 127 bit Gold-series. This multi-channel en-decoder can be used in OCDMA/WDM hybrid system..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1522 (2007)
Rapid Communications
[in Chinese]
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1600 (2007)
Reviews
Optical Properties of Gold Nanoparticle and Its Application in Biological Imaging and Photothermal Therapy
[in Chinese], [in Chinese], [in Chinese], [in Chinese], [in Chinese], and [in Chinese]
Nanoparticles have attracted widespread interest in molecular biology and medicine fields for diagnostic application and biological imaging, due to their unique optical properties and facile surface chemistry. Noble metals, especially gold nanoparticles (NPs), have great potential use in biological issue imaging, canceNanoparticles have attracted widespread interest in molecular biology and medicine fields for diagnostic application and biological imaging, due to their unique optical properties and facile surface chemistry. Noble metals, especially gold nanoparticles (NPs), have great potential use in biological issue imaging, cancer diagnosis and therapy because of their surface plasmon resonance (SPR) and strong absorption induced luminescence. Au-ligand conjugates can specifically target the receptor on cancer cells, provide specific information about specific molecules, and allow molecular-specific imaging and cancer detection. Gold NPs can strongly absorb light, efficiently convert optical energy into localized heat, produce selective photothermal effect, and induce protein denaturation and cells death. The optical and photothermal properties of gold NPs are summarized, and the research progress of selective targeting of gold NPs in biological imaging, cancer diagnoses and photothermal therapy is reviewed..
Chinese Journal of Lasers
- Publication Date: Jan. 01, 1900
- Vol. 34, Issue 11, 1459 (2007)
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