光纤激光器光参量啁啾脉冲放大现象

实验研究了采用信号光在一块非线性晶体内被同一束泵浦光放大两次的结构来实现光参量啁啾脉冲放大过程中对参量荧光的控制,实验得到了2×106的双通总增益,输出总能量为2 mJ,信号光能量晃动小于3％ rms,此时参量荧光仅占输出总能量的1％.采用这种放大结构,提高了短信号光与长泵浦光在时域上的匹配和转换效率,抑制了参量荧光,并提高了放大信号光的能量稳定性.     

Noncollinear second harmonic generation in KDP

This paper reports experimental and analytical results on optical second harmonic generation when a noncollinear arrangement is employed. The dependence of second harmonic power on crystal length, absorption, beam radius and the angle between the two fundamental waves is obtained. Double refraction of the crystal is taken into account, but the divergence and depletion of the fundamental waves are neglected. The results of the calculations are confirmed by experiments carried out with a KDP crystal in the near field of two intersecting TEM₀₀ ruby laser beams.An extension of the theory to nonlinear interactions other than second harmonic generation - e.g. four-wave interaction - is possible.     

非线性一维光子晶体波导光双稳

利用非线性折射率系数较大且非线性时间响应较快的CdS_xSe_1-x玻璃为材料,设计并制备了非线性一维光子晶体波导光双稳器件,该器件的折射率空间分布呈正弦形式。实验测得双稳开关的阈值功率密度为1.60×10⁵W/cm²,开关时间为63ps。采用时域有限差分方法讨论了光子晶体带隙随入射光强变化而移动的情况,随着入射光功率密度的增加,光子晶体的带隙中心向短波方向移动。同时计算了该器件的双稳特性,理论计算得到双稳开关的阈值功率密度为1.40×10⁵W/cm²,开关时间约为50ps。获得了理论与实验基本一致的结果。     

Computer simulation and observation of anomalous light emission from nonlinear photonic crystal with various geometry of its elements

Recently, in papers [1, 2] were described the effect of long-time emission of photonic crystal (synthetic opals) under the action of nanosecond laser pulse. The duration of the luminescence is of the order of seconds. Despite on the other phenomena, which were considered in these papers, below we focus our attention on possible explanation of long time emission from nonlinear photonic crystal. The basis of our consideration is papers [3, 4], those deal with soliton formation in several layers of 1D nonlinear photonic crystal. Because of this, the light wave can exist in photonic crystal a long time (in ideal case—infinite time interval). Taking into account a relation between soliton duration and its maximum intensity, the leaving of laser energy from the layer of photonic crystal takes place due not full reflection from boundaries of layer. The time of light emission for this case depends on nonlinear susceptibility of photonic crystal and the intensity of laser pulse. Hence, soliton formation inside the nonlinear elements of photonic crystal can be one of the reasons of long time emission. We got in computer simulation a long time emission of 1D (layered) and 2D (circular or rectangular elements) nonlinear photonic crystal under the action of laser pulse with femtosecond duration under the conditions of soliton formation in some elements of photonic crystal. Input intensity of laser pulse, at which a soliton appears in nonlinear photonic crystal, can be ten times less due to effects of enhancement of optical intensity in periodic structure [4, 5].     

高稳定LD端面泵浦腔内倍频Nd∶YVO4/LBO连续红光激光器

设计出一种能够较好地补偿激光晶体热效应的激光谐振腔,实现了高稳定LD单端泵浦LBO腔内倍频Nd∶YVO4连续红光激光器.当晶体吸收的泵浦功率为24.56 W时,671 nm激光功率达到1.203 W,光-光转换效率4.9%,激光模式为TEM00模.在输出功率为1.08 W时,激光器1 h功率不稳定度为0.52%.     

A comparative study on dual colour soft aperture cascaded second-order mode-locking with different nonlinear optical crystals

A comparative study in terms of optimized output power and stability is made on cascaded second-order nonlinear optical mode-locking with KTP, BBO and LBO crystals for both 1064 nm and 532 nm. Large nonlinear optical phase shift achieved in a non-phase-matched second harmonic generating crystal, is transformed into amplitude modulation through soft aperturing the nonlinear cavity mode variation at the laser gain medium to mode-lock a Nd:YVO4 laser. The laser delivers stable dual wavelength cw mode-locked pulse train with pulse duration 10.3 ps and average power of 1.84 W and 255 mW at 1064 nm and 532 nm respectively for the optimum performance in type-II KTP crystal. The exceptional stability achieved with KTP is accounted by simulating the mode-size variation with phase mismatch.     

高稳定LD泵浦腔内倍频Nd∶YVO4/KTP连续绿光激光器

设计出一种能够较好地补偿激光晶体热效应的激光谐振腔，实现了高稳定LD单端泵浦KTP腔内倍频Nd∶YVO₄连续绿光激光器.当晶体吸收的泵浦功率为24.56 W时，532 nm激光功率达到5.3 W，光-光转换效率达到21.6％，激光模式为TEM00模.在输出功率5W左右时，激光器1 h功率不稳定度优于0.6％     

富勒烯有机-无机杂化材料的非共珍三阶非线性光学特性

采用中心波长800 nm、脉宽30 fs的超短激光脉冲,通过飞秒光开关技术(Optical Kerr Shutter,OKS)对富勒烯有机-无机杂化材料的飞秒超快非线性特性进行了实验研究.获得270 fs的开关时间,所得的富勒烯有机-无机杂化材料的三阶非线性系数X~(3)约为4.5×10~(-4) esu,比C_(60)分子的三阶非线性系数X~(3)高一个数量级.通过实验测定的光克尔信号强度与激发光和探测光偏振方向夹角的依赖关系表明:30 fs的超短激光脉冲激发富勒烯有机-无机杂化材料的克尔信号主要是源于光诱导双折射效应,而非用200 fs的超短激光脉冲时来自瞬态栅的自衍射效应.     

富勒烯有机-无机杂化材料的非共珍三阶非线性光学特性

采用中心波长800 nm、脉宽30 fs的超短激光脉冲,通过飞秒光开关技术（Optical Kerr Shutter,OKS）对富勒烯有机-无机杂化材料的飞秒超快非线性特性进行了实验研究.获得270 fs的开关时间,所得的富勒烯有机-无机杂化材料的三阶非线性系数χ(3)约为4.5×10－14 esu,比C60分子的三阶非线性系数χ(3)高一个数量级.通过实验测定的光克尔信号强度与激发光和探测光偏振方向夹角的依赖关系表明：30 fs的超短激光脉冲激发富勒烯有机-无机杂化材料的克尔信号主要是源于光诱导双折射效应,而非用200 fs的超短激光脉冲时来自瞬态栅的自衍射效应.     

Intensity dependence of thermal nonlinear optical activity in crystals

The thermal contribution to nonlinear optical activity in a BSO crystal was studied at 514.5 nm. The results show that the effect is only weakly dependent on laser intensity for constant beam power. By varying the laser spot size in the sample the electronic and thermal contributions to nonlinear optical activity may be separated.     

Ultrafast switching dynamics of nonlasing modes of vertical-cavity surface-emitting lasers

Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with ultrafast optical modulation. After injection of a subpicosecond laser pulse into the VCSEL cavity, nonlasing modes were excited and produced optical beating in the emission of the VCSEL. After these oscillations have died down, when the VCSEL is operating at high power and when the injected laser pulses exceed a power threshold as well, the injected laser pulses can induce the lasing to switch to a normally nonlasing mode with crossed polarization. Our measurements of the decay time of the nonlasing modes at low injected pulse energy are consistent with the interpretation of this switching as enabled by increased lifetime of the nonlasing modes at high power.     

高功率中红外3.8 μm激光器

采用1.06 μm激光泵浦准相位匹配周期极化铌酸锂（PPMgLN）晶体光参量振荡器,实现高功率高效率高重复频率3.84 μm中红外激光输出。泵浦源为椭圆光斑1.06 μm激光,PPMgLN晶体MgO摩尔分数为5%,光参量振荡器为外腔单谐振结构,采用e→e+e相位匹配,利用了PPMgLN晶体的最大非线性系数。在1.06 μm激光功率为73 W,声光Q开关工作频率为7.5 kHz的条件下,获得平均功率8.3 W,波长3.84 μm激光输出,光-光转换斜率效率14.1％,水平和垂直方向光束质量平方因子分别为1.94,4.57。     

基于非线性偏振旋转锁模的高功率光子晶体光纤飞秒激光振荡器

为了探索大模场面积光子晶体光纤锁模激光器在全正色散锁模域内的耗散孤子锁模机理, 以获得更大的单脉冲能量和更高的峰值功率, 本文搭建了以掺镱大模场面积光子晶体光纤作为增益介质的耗散孤子锁模激光器. 激光器使用环形腔结构, 利用非线性偏振旋转以及滤光片提供的耗散作用实现了稳定的锁模运转. 实验中, 从激光器振荡级直接获得了平均功率10 W, 重复频率49.09 MHz(对应202 nJ的单脉冲能量), 脉冲宽度为1.03 ps的稳定锁模脉冲输出, 经过腔外色散补偿得到的脉冲宽度为95.5 fs.     

Crystal structure,vibrational, and optical investigations of semiorganic nonlinear optical crystal: Bi3[CS(NH2)2]9Cl9· 2H2O

Tribismuthnonakisthioureanonachloride dihydrate (TBNTNC), a semiorganic nonlinear optical (NLO) material useful for frequency doubling in the IR region, has been grown by single diffusion gel technique. The grown crystal was confirmed by single crystal XRD and it crystallizes in triclinic system having P₁ space group. Vibrational analysis was carried out for the grown crystal. FTIR and FT‐Raman spectral studies were performed for analyzing and assigning the phonon vibrations and to identify the functional group contribution. The optical transmission study was carried out to examine the transmission ability of the crystal. The nonlinear optical property was confirmed by relative second harmonic generation measurement using Nd:YAG laser. Copyright © 2009 John Wiley & Sons, Ltd.     

非线性光栅的自适应光限幅

首次采用液晶为自聚焦媒质,夹在内表面刻有光栅的两玻璃片间,以Ar离子激光514.5nm波长的激光束垂直入射到光栅上,实验验证了该光栅的自适应光限幅特征。     

1 064 nm激光对氧化铟锡薄膜的损伤研究

 液晶光学器件在激光光束精密控制上具有重要应用前景,氧化铟锡（ITO）薄膜作为液晶光学器件的透明导电电极,是液晶器件激光损伤的薄弱环节。为此,建立了ITO薄膜激光热损伤物理模型。理论计算结果表明：1 064 nm激光对ITO薄膜的损伤主要为热应力损伤;连续激光辐照下,薄膜损伤始于靠近界面的玻璃基底内;脉冲激光辐照下,温升主要发生在光斑范围内的膜层,薄膜损伤从表面开始。利用泵浦探测技术,研究了ITO薄膜的损伤情况,测量了不同功率密度激光辐照后薄膜的方块电阻,结合1-on-1法测定了ITO薄膜的50%损伤几率阈值。实验结果表明：薄膜越厚,方块电阻越小,激光损伤阈值越低;薄膜未完全损伤前,方块电阻随激光功率密度的增加而增大。理论计算与实验结果吻合较好。设计液晶光学器件中的ITO薄膜电极厚度时,应综合考虑激光损伤、透光率及薄膜电阻的影响。     

远红外固体激光器研究进展

8～12μm波段是大气的一个窗口,被定义为长波红外波段。该波段激光对雾、烟尘等具有较强的穿透力,在激光光电对抗、激光遥感、医疗、环境监测及光通讯领域具有重要的应用前景。本文调研了常用的8～12μm非线性频率变换晶体,以及基于非线性频率变换晶体的远红外光参量振荡器的研究进展,对国内外能实现8～12μm波段激光输出的非线性晶体及激光系统进行了系统地归纳和总结,通过分析比较得出在8～12μm波段获得的最大输出能量为毫焦量级,最大功率为瓦量级。国内该技术与国外有着不小的差距,主要受制于高重频、高功率脉冲1～3μm泵浦源技术不成熟及高性能非线性晶体材料研制基础薄弱,我国在长波远红外固体激光器领域研究进展缓慢,因此研制大尺寸、高质量远红外激光晶体及输出波长更长的远红外高功率激光器已经成为激光器未来发展方向之一。     

Photonic crystal-based all-optical arithmetic circuits without SOA-based switches

Various proposed optical computing devices involve nonlinear optical operation and use semiconductor optical amplifier (SOA)-based switches as fundamental elements for logic operations. Due to the nonlinear operation, these devices suffer from high power that causes problems in very large-scale optical integration. In this paper, a method is proposed to implement arithmetic operations using a photonic crystal (PhC) cell and eliminate the SOA-based switches altogether. The proposed method is employed on designing an all-optical full adder/subtractor circuit that requires only beam combiners and photonic crystal NOT gates.     

End-pumped optical bistability Tm,Ho:YLF laser

We experimentally demonstrate strong optical bistability in a 2 μm continuous wave Tm,Ho:YLF laser with a bulk crystal. The laser is end-pumped by a 792 nm fiber-coupled laser diode. The bistable region is as wide as 1.6 W and the jump power at the turning point is as high as 82.5 mW when the temperature of the laser crystal is kept at 253 K. The influences of the cavity length and the transmission of the output coupler on the characteristics of optical bistability are obtained. The theoretical analysis shows that the bistable output in the Tm,Ho:YLF lasers comes from the combined effects of the nonlinear saturation of ground state reabsorption, the energy transfer upconversion, and the excited state absorption.     

Four-wave mixing in dual wavelength fiber laser utilizing SOA for wavelength conversion

In this paper, a novel configuration of a wavelength converter is set forth by utilizing a semiconductor optical amplifier (SOA) as a nonlinear gain medium to generate a four-wave mixing (FWM) effect by using a dual wavelength bi-erbium-doped fiber laser that uses an Arrayed Waveguide Grating (AWG) together with two optical channel selector (OSC) as selective elements to function as a dual wavelength switchable pump power. The four-wave mixing (FWM) is produced with a wavelength detuning of 7 nm from the pump and signal which used is as the converted signal at wavelength 1532.8 nm or 1534.5 nm for transferring data from the input signal at wavelength 1547.0 nm. Thus, even though the conversion efficiency is as low as −43 dB, it is still possible for applications as a wavelength converter.