The effect of surface morphology on laser-induced crystallization of hydrogenated intrinsic amorphous silicon (a-Si:H) thin films deposited by PECVD is studied in this paper. The thin films are irritated by a frequency-doubled (λ=532 nm) Nd:YAG pulsed nanosecond laser. An effective melting model is built to identify the variation of melting regime influenced by laser crystallization. Based on the experimental results, the established correlation between the grain growth characterized by AFM and the crystalline fraction (Xc) obtained from Raman spectroscopy suggests that the crystallized process form amorphous phase to polycrystalline phase. Therefore, the highest crystalline fraction (Xc) is obtained by a optimized laser energy density.
The laser performance of a short-length Yb-doped rod-type photonic crystal fiber (PCF) laser is studied experimentally both in the three-level scheme and quasi-four-level scheme in this contribution. In the free oscillation mode, the rod-type PCF laser produce 13.6 W output power on the quasi-four-level system with center wavelength of 1030 nm. The laser operating on the three-level system is obtained with the introduction of specialized feedback around the 976 nm radiation. Up to 7 W output power is generated with wavelength centered in 978 nm.
We demonstrate a passive coherent beam combination of two nanosecond amplifiers by using an all-optical feedback loop. An electro-optic amplitude modulator is utilized to tune the pulse width and the pulse repetition frequency of combined laser pulse. The positive correlation between the visibility of far-field coherent patterns and the pulse duty ratio is found. The range of tunable pulse repetition frequency is from 2.023 MHz to 6.069 MHz, and the range of tunable pulse width is from 10 ns to 50 ns. The maximum visibility is up to 85%. This approach presented here provides a promising way for power scaling of high power nanosecond fiber laser and maintaining beam quality simultaneously.
Laser-induced fluorescence (LIF) of high-purity fused silica irradiated by ArF excimer laser is
studied experimentally. LIF bands of the fused silica centered at 281nm, 478nm and 650nm are
observed simultaneously. Furthermore, the angular distribution of the three fluorescence peaks is
examined. Microscopic image of the laser modified fused silica indicates that scattering of the
generated fluorescence by laser-induced damage sites is the main reason for the angular distribution
of LIF signals. Finally, the dependence of LIF signals intensities of the fused silica on laser power
densities is presented. LIF signals show a squared power density dependence, which indicates that
laser-induced defects are formed mainly via two-photon absorption processes.
The inscription method of FBGs on large-mode-area double-clad fibers (LMA-DCFs) with phase mask technique was
described. A pair of LMA FBGs was prepared and the center wavelengths of them were both around 1076nm with 3 dB
bandwidths of about 0.5nm. The reflectivities of them are 99% and 10% in the fundamental mode, respectively. In order
to be protected and to withstand high-power laser, the FBGs were metally packaged, and then applied to an Yb<sup>3+</sup>-doped
LMA-DCF laser as the laser cavity. An output power of 314 W centered at 1075.71 nm with a slope efficiency of 60%
A master-oscillator fiber power amplifier system with a 4.5-m-long Yb3+-doped homemade large-mode-area double-clad fiber is reported. Up to 156 W average power of 1064 nm amplified pulse, corresponding to a slope efficiency of 64.9%, has been demonstrated. The amplified pulse possesses a pulse duration of 24 ns and a repetition rate of 50 kHz and demonstrates a good beam quality (M=2.81 and M=2.66), although no special transverse-mode-controlling techniques were adopted.
Based on the frustrated total internal reflection theory, a leaky large-mode-area double clad fiber is
designed. The propagation constants and leakage loss of the fundamental mode LP<sub>01</sub> and sub-low order
mode LP<sub>11</sub> is investigated by using of the matrix method. Results show that the designed fiber can
operate with single-mode.
A narrow-linewidth master-oscillator fiber power amplifier system with homemade large-mode-area fiber is
demonstrated. Some fundamental characteristics of this system, including the output power characteristics, the emission
spectrum characteristics, as well as the confirmation of single-frequency operation are investigated in detail. The system
generates up to 7.3 W of single-frequency radiation at a wavelength of 1064 nm with 39% slope efficiency and 26%
optical-optical power conversion efficiency.
The authors report stable short high-repetition-rate Q-switched pulses in acousto-optic Q-switched ytterbium-doped
double-clad fiber lasers. This device uses a diode pumped at 975 nm to end pump the large mode area double-clad fiber
laser. In the experiment acousto-optic modulator is used as a special Q-switching in the F-P cavity. As a result, sub 100
nanosecond pulses are obtained with varying the acoustic-optic repetition rate from 1 kHz to 100 kHz. The Q-switching
technique provides a novel method to generate short pulses at high repetition rate.
Fiber Lasers are most powerful solid state lasers available for various applications, they are capable of providing diffraction, limited power with compact, efficient and cost effictive system. In this paper, we report a master, oscillator fiber power amplifier for pulsed operation from 20kHz to 100kHz. A 4m double cladding fiber has central core of 43um and inner core of about 600/650um is used as amplifier, the seed source is a pulsed laser with output power of 1 W at 1064nm. A fraday isolator protect the seed laser from backflection from fiber amplifier. The MOPA system is analysied by transient gain model, pulsed amplified characteristics of double cladding fiber are caulated and compared with experimantal results at different pumping power and repetition rate.The fiber amplifier is pumped by laser diode at wavelength of 795nm with pumping power of 230W, the system can emits average power upto 133.8 W with repetition rate of 100kHz.
Polycrystalline ceramic Nd:YAG laser material enables new possibilities in designing the laser medium
with respect to dopant, size and geometry. In this paper, a 184W continuous-wave Nd<sup>3+</sup>-doped ceramic
Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (Nd : YAG) laser with optical to optical efficiency of about 44.3% has been developed. Laser output
power characteristics as well as the thermal lensing and birefringence properties of the ceramic laser rods were
investigated. The sample used in this experiment was a 3.5mm diameter, 87mm long ceramic YAG rod with
0.6% Nd<sup>3+</sup> concentration. And the end faces of the rod were flat and antireflection-coated at 1064 nm. The
pumping geometry used in this work was a diffusive optical cavity with narrow slits for side-pumping.
A master-oscillator fiber power amplifier (MOPA) system with a 4-m-long Yb3+-doped homemade large mode area (LMA) double-clad fiber is reported. The system emits up to 133.8 W of amplified radiation at a wavelength of 1064 nm and a repetition rate of 100 kHz, limited only by the available pump power. Peak power of 300 kW at 20 kHz with a pulse duration of 15 ns is obtained.
The performance of long-haul dispersion managed DWDM soliton systems is systematically studied. It is found that the values of Q factor and optimal window for some channels are very different. The optimized bandwidth of inserted optical filter and dispersion map are suggested.
A high power Ytterbium-doped fiber laser (YDFL) with China-made double clad fiber (DCF) is introduced in this paper. The Geometric parameter and laser characteristics of the newly designed fiber have been studied. When both ends of the fiber were pumped by two
high-power laser diode with the total lunched power about 600W , we got the laser output of 330W, with an optical-to-optical efficiency of 55%.
We simulated beam combination of Yb-Doped Double-Clad-Fiber(DCF) lasers theoretically by using a new external cavity and this system suits both of 1D array and 2D array. The numerical simulation result of 1D linear array shows that light energy from fiber lasers can be coupled into fiber cores through a single round trip. In comparison with several 2D arrays, we find that both the radius of the central spot shroten with the number of fibers increasing, on the contrary, the optical feedback through a single round trip coupled into cores increase gradually.
This paper introduces ZnO semiconductor optical amplifiers. In this paper, stimulated emission from zinc oxide nanoparticles are discussed in low and high powder density samples. 4 nm linewidth emission peak are observed in ZnO nanoparticles pump by Nd:YAG laser with 8 ns pulse width in high powder density sample. Scattering is strong when the nanoparticle density is high. And strong scattering is the reason of narrow peak in the nanoparticle. We also investigate the influence of the excitation spot area and the scatter concentration on the laser threshold in the TiO<sub>2</sub>/Rhodamine B gain media, with frequency-doubled output of a mode-locked Nd:YAG laser (20 Hz repetition rate, 6 ns pulse width). Monte Carlo methods with ring laser were employed to calculate the threshold gain required for modeling the input-output characteristics in scattering gain media. We performed a Monte Carlo simulation of random walks in the geometry. With the increased pump area, the laser threshold is decreased. If we add more scatterers in the Rhodamine B, the laser threshold will reduce.
The heat generation in a flashlamp-pumped Nd:glass disk amplifier is studied by the simulation of the whole pumping process, which is based on the ray-tracing method. The results of temperature rise distribution as well as gain distribution are presented. The evolution of heat generation in disk during the pumping process is discussed in detail. Some main factors related with the thermal effect, such as the quantum efficiency, fluorescence lifetime, and pulse duration, are investigated through studying the ratio of the heat generation to energy storage in the gain medium. The influence of each parameter on heat generation is studied carefully, and the results provide ways to decrease the heat generation during the pumping process.
A novel trapezoid prism homogenizer is used to improve the uniformity of output energy density of excimer laser. The principle and the design requirements of the novel trapezoid prism are analyzed theoretically, and the optimal position of uniform section is calculated. Using this novel homogenizer, the fluctuation of beam uniformity of XeCl excimer laser is less than 4%. The result is better than that obtained from a normal prism homogenizer. The evaluating norms of excimer laser beam uniformity are analyzed in detail. The process window defines uniformity requirements of excimer laser, while the energy fraction answers the problem of useful percentage of energy within a giving process window. The top-hat factor defines the uniformity in the whole energy range, and the dynamic range is the variation range of screen-homogenizer in the specific application. Using this evaluating norm the uniform beam obtained by the novel trapezoid prism homogenizer is analyzed.
A new method for side-pumping double-cladding fiber was researched. A quartz column of 3mm length was cut away from D-shape double-cladding fiber which has a transverse sectional dimension of 350μm×400μm. Then the column-fiber coupler was fabricated by gluing the column onto the side of inner cladding . The pumping light was coupled into the inner cladding from the end of the D-shape quartz column. When the output power was 1.3W from the forward end of the coupler, the optimum efficiency is 85%. This method can be suitable for pumping the fiber laser and amplifier of several watts output power.
A highly efficient Yb doped double clad fiber laser, one end pumped by a 975nm diode attack source and generating up to 115.6 of CW output power at 1100nm is reported in this paper, the maximum optical-optical conversion efficiency is 79% and the slope efficiency is about 69%. The frequency doubling of the fiber laser is obtained with conversion efficiency of 6% by using PPLN as nonlinear optical material.
The output characteristics of double cladding fiber laser are investigated pumped by 915nm and 975nm diode lasers. The average effective absorption coefficients for two kinds pump wavelengths are given. A 20W Ytterbium - doped fiber laser in 1110nm region with near diffraction limited beam spread angle are reported.
The wavelength characteristics of Yb<sup>3+</sup>-doped double cladding fiber are investigated pumping by 915nm and 975nm high power laser diode respectively. The relationship between the pumping power and pumping wavelength on laser output are measured and discussed in detail.
We will discuss reults of the experimental and theoretical study of the low-frequency noise in GaN/AlGaN 2D structures and examine possible sources of noise, including contacts, surface and 2D channel itself. 2D GaN/AlGaN heterostructures exhibit a much small level of 1/f noise than bulk GaN films. In the frame of model linking noise to the tail states, this might be explained by a high degeneracy of the 2D electrons in this structures. Due to the electron degeneracy, the tail states mechanism of the 1/f noise is suppresed in GaN-based 2D structures. Our measurements show that contacts does not contribute much to overall low frequency niose. Concentration dependence of the Hooge parameter points out to the tunneling mechanism of noise in these structures.
In this paper, the principles of laser-materials interaction by UV laser have been reviewed. In addition, several successful applications by using pulsed UV laser including surface treatment, surface ablation as well as formation of nanometer particles have been presented.
Graft copolymerization of acrylamide (AAm) onto poiy (ethylene terephthalate) using a XeC1 excimer laser was performed to improve surface hydrophilicity. Laser irradiation and graft polymerization were conducted simultaneously. The samples treated were characterized by contact angle measurements, XPS analysis, and microscopic observation. The surface hydrophilicity was improved significantly after AAm was grafted onto the film. The factors influencing the graft reaction were studied to understand the mechanism of laser-induced graft polymerization, deducing that a peroxide-initiated radical polymerization occurs during laser-induced graft polymerization. The N/C ratio of the surface changed from nil for untreated sample and irradiated but non-grafted sample to 0. 11 for grafted sample. The O/C ratio increased gradually in the order of untreated, irradiated but non-grafted and grafted under the chosen treatment condition. Carbon particles formed on the grafted surface as higher laser fluence was employed were observed.
UV-laser induced changes on surface structure and properties of Poly(ethylene terephthalate) (PET) fabric were discussed. Scanning electron microscope (SEM) observation revealed the morphological modification of PET fabrics with the ablation of 308nm excimer laser. The contact angle measurement and vertical drop test were used to find out the difference in the wetting property of the untreated and laser ablated PET fabric. Extra carboxylic radicals and increased amorphous part on the surface of the laser-ablated fabric were estimated by the attenuated total reflectance Fourier-transform infrared spectrum (ATR FT-IR) analysis. Dyeing property of the PET fabric was changed evidently by laser irradiation.
In this study, high efficient backward Raman compression has been achieved by a 10J KrF pump laser from Heaven-1 MOPA system using focused-beam geometry. A preliminary stage of experiments was carried out in CIAE with main results reported here. Up to 1.7J of first backward Stokes(268nm) output with pulse duration of 1.5ns was obtained as the pump (248nm) laser was 1OJ of energy and 22ns of pulse duration. The pulse duration is compressed by 15 times with total energy conversion efficiency up to 17%. The high conversion efficiency of backward SRS is considered mainly attributing to the focused geometry. The mechanisms of backward Stokes pulse self-shortening and forward-backward gain asymmetry compensating have been discussed. The backward Stokes pulse duration is considered to be much less than it was observed using a relatively lower bandwidth oscillograph. Further experimental research on precision time measurement will be performed later this year.
The fiber laser's excellent focus and efficiency, small size and light weight makes it highly promising not only for telecommunication, but also for industry and medical applications. In a double clad fiber laser, the inner cladding for guiding the pump light is provided around a core doped with active ion (e.g. YB3+, Nd3+, Er3+, etc.). The recent progress of fiber laser is reviewed at first in this paper. Different shapes of inner cladding are investigated to increase the pumping efficiency. Beam-shaping optics deliver high-power beams as the pumping source is discussed. Finally, a 4.9W cw double-clad fiber laser demonstration experiment in SIOM is described.
In this paper, We have proposed a new cross section shape of inner cladding benefited from the conception of unsteady cavity in laser technology. The absorption characteristic of this new type double-clad fiber is analyzed in detail with ray tracing method. For this new type and rectangular double-clad fibers, with core diameter 8im and pump area 100?mX 100?m, about 98% pumped propagation rays are absorbable after 100 times reflection in the inner cladding, so it is possible to achieve very high absorption efficiency. However, for circular, offset and D shape double-clad fibers, with same core diameter and pump area above, only 10%, 50%,80% pumped propagation rays are absorbable.
A relative good and economical method has been presented to fabricate V-grooves on LiNbO<SUB>3</SUB> crystal for passive fiber alignment. It ha been experimentally investigated of excimer laser ablated V-grooves on LiNbO<SUB>3</SUB> crystal. Two excimer lasers were employed for comparison experiment with the wavelength of 308nm and 193nm respectively. It has been shown that 308nm wavelength performed a poor role in fabricating grooves on LiNbO<SUB>3</SUB> crystal, particularly on both ablation sped and surface quality, while 193nm wavelength showed excellent performance. The corresponding ablation threshold of LiNbO<SUB>3</SUB> crysatl at 193nm has been found to be as low as 0.5J/cm<SUP>2</SUP>. At laser fluence of 3J/cm<SUP>2</SUP> and 1200 shots of laser irradiation, V-grooves with some 130 micrometers have been fabricated without visible damage near the grooves. Oxygen buffering atmosphere has been utilized for improving ablation surface cleansing.
In this paper, a fast process of fabrication of diffractive optical elements by excimer laser ablation of polymer films is mainly described. Dammann grating on PI and PC materials with feature size of 2 micrometers are successfully fabricated.
In this paper, a fast process of fabrication of diffractive optical elements by excimer laser ablation of polymer films is mainly described. For fabrication of a two-level diffractive element, fewer steps and less time are needed.
In this paper, the direct ablation of polymer films of PMMA, PI, PC and K9 glass has been studied at wavelengths of 193 nm and 308 nm. The ablation characteristics of microstructuring is mainly discussed and compared. The ablation qualities of PC, PMMA and K9 glass by XeCl (308 nm, 30 ns) excimer laser are very poor. The ablation performances of PMMA and K9 glass by ArF (193 nm, 17 ns) excimer laser are medium. Smooth surfaces and sharp edges with micron transverse resolution and submicron depth precision can be obtained by the ablation of PI at 308 nm, and PI, PC at 193 nm.
In this paper, the direct ablation of polymer films of PMMA, PI, PC and K9 glass has been studied at wavelength of 193nm and 308nm. The ablation characteristics of microstructuring is mainly discussed and compared. The ablation qualities of PC, PMMA and K9 glass by ArF excimer laser are medium. Smooth surfaces and sharp edges with micron transverse resolution and submicron dep precision can be obtained by the ablation of PI at 308nm, and PI, PC at 193nm.
For flexible structuring of a great variety of materials such as polymers ceramics and glass materials, excimer laser radiation has turned out to be a particularly appropriate tool. The excimer laser etching enables the manufacturing of micro-holes and grooves in the micrometer range, as well as the production of complex 3D topographies. In this paper, the surface characteristics of polymer and glass are compared after been etched by 308nm and 197nm UV excimer lasers, the results show that the use of ArF laser allows processing a surface quality close to that of the optics and fabricating ridges about 2micrometers - width. Finally, a rotational mask system is proposed to generate Fresnel lens.
A new technique for surface modification of polymer fibers is introduced by irradiating with UV an excimer laser, this technique can be used to modify the chemical and physical properties of fibers surface. Under certain conditions the irradiation of polymer fibers induced a characteristic morphology on the polymer fiber surface. The original smooth surface of polymer fibers changes its morphology to a rather regular roll-like structure perpendicular to the fiber axis after this treatment. The dependence of characteristic surface data on laser fluency and pulse number are studied. The mechanism for formation periodic surface is also discussed.
Beam-deflection technique was used to monitor the surface treatment of fullerence films near the ablation threshold region. When the fullerence films were irradiated by UV excimer laser with fluence below the ablation threshold, an increase of the electrical conductivity of up to six orders of magnitude was observed. The products resulting from the laser irradiation have been investigated by Raman spectroscopy.
The damage threshold of ZrO<SUB>2</SUB>/SiO<SUB>2</SUB> and HfO<SUB>2</SUB>/SiO<SUB>2</SUB> thin films was investigated in gas chamber (with oxygen gas, air, helium gas or vacuum condition) by using a scattering detector system. The experimental results show that the damage threshold is increased about 20% in oxygen gas ambient. The mechanism of these phenomena is discussed.
A polymer surface treatment irradiated system by XeCl excimer laser is designed, bond strengths are measured by shear test method. The bond strengths of fluorocarbon-resin with aluminous bar is improved by solutions such as water (H<SUB>2</SUB>O), boric acid (H<SUB>3</SUB>BO<SUB>3</SUB>), sodium hydroxide (NaOH), bluestone (CuSO<SUB>4</SUB>), sodium aluminate (NaAlO<SUB>2</SUB>) reacting with fluorocarbon-resin while XeCl excimer laser irradiating. The relationship between the adhesion force with the laser intensity and laser pulse shots are measured. The mechanism of these phenomena is discussed.
In this paper, the quenched dye lasers pumped by XeCl and KrF excimer lasers were investigated theoretically and experimentally. Dye laser pulses with duration of 0.8 ns for XeCl laser pumping and 2 ns for KrF laser pumping were obtained.
After being irradiated in air by XeCl (308 nm) excimer laser, the electrical conductivity of solid thin-film C<SUB>60</SUB> has been improved by more than six orders of magnitudes. The products resulting from laser irradiation of C<SUB>60</SUB> films have been investigated by Raman scattering and the onset of conductivity can be attributed to laser-induced oxygenation and disintegration of fullerene. Irradiated by approximately 40 ns laser pulses with different fluence, the products with different microstructure were observed. At lower fluence, the Raman features of microcrystalline graphite and fullerene polymer were observed. At a fluence just below the ablation threshold (36 mJ/cm<SUP>2</SUP>), the fullerene molecules in film were disintegrated completely and transformed to amorphous graphite.
The link of a XeCl excimer laser, a hydrogen Raman cell, and a Ti:Al<SUB>2</SUB>O<SUB>3</SUB> laser oscillator to form an integrated laser system is proposed to offer wavelength diversity for laboratory uses. The performance of the Raman conversion and the tunable output of Ti:Al<SUB>2</SUB>O<SUB>3</SUB> laser is presented in detail.
By measuring the effects of halogen concentration on the lifetime of KrF excimer laser, the impurities effects on the laser output performance are analyzed. The experimental results also show that the degration of halogen concentration is related to the laser resonator conditions.
In this paper, the ablation processes were investigated using light deflection spectroscopy as a detection method. The cumulative effect of PMMA near the ablation threshold was studied in detail, and the cutting-edge quality of photoablation was improved to some extent by a nitrogen gas stream.
The transverse gas flow excimer laser with x-ray and UV preionization were used to investigate the gas flow effects on the performance of XeCl laser. The density disturbances created by high input power density and nonuniformity of the gas velocity along the optical axis will reduce the laser power at high repetition rate.
A long pulse one Joule excimer laser was used as a pumping source
for stimulated Raman scattering in lead vapour and hydrogen. High
efficiency Raman frequency conversion into blue-green region was
obtained . A decrement of Raman conversion efficiency at high
repetition rate was observed in a sealed Raman cell. A hydrogen
gas circulating system was designed with gas pressure up to 50
Atm,it can be operated at high repetition rate without decrement
of Raman conversion efficiency.