Fiber bragg gratings made with a phase mask and 800-nm femtosecond radiation

High-quality retroreflecting fiber Bragg gratings were written in standard Ge-doped telecom fiber (Corning SMF-28) after a few minutes exposure with pulsed 800-nm, 120-fs laser radiation by use of a deep-etch silica zero-order nulled phase mask optimized for 800 nm. Induced index modulations of 1.9 x 10(-3) were achieved with peak power intensities of 1.2 x 10(13) W/cm2 without any fiber sensitization. The fiber gratings are stable and did not erase after 2 weeks at 300 degrees C. The primary mechanism of induced index change results from a structural modification to the fiber core.     

Bragg grating recording in low-defect optical fibers using ultraviolet femtosecond radiation and a double-phase mask interferometer

The fabrication of Bragg reflectors in fluorine depressed cladding silicate glass and SMF-28 fibers by employing a double-phase mask interferometer and 248 nm, 500 fs laser radiation is demonstrated here. The maximum refractive index changes obtained were of the order of 6 x 10(-4) for pulse intensities of 220 GW/cm(2) and accumulated energy densities of 3.5 kJ/cm(2). The Bragg gratings fabricated in the F-doped fiber endured temperatures greater than 700 degrees C, while those inscribed in the standard telecom fiber demarcated at 900 degrees C. The experimental results presented depict that the combination of the two phase mask interferometer and the 248 nm photon at sub-TW/cm(2) intensities constitute an efficient route in the fabrication of Bragg gratings in low-defect silicate glass optical fibers.     

Planar Bragg gratings made by excimer-laser modification of ion-exchanged waveguides

The refractive indices of planar silver-ion-exchanged waveguides have been modified by UV excimer laser irradiation (lambda=193 nm) . The effective index changes of the fundamental modes of the waveguides after exposition are as large as 2x10(-2) . The procedure permits the fabrication of integrated optical components in a direct way, with neither the use of standard lithography nor previous sensitizing of the substrate. Optical characterization of the irradiated samples is presented. By the use of appropriate masks, we have fabricated planar Bragg gratings.     

Effect of composition gradient on CuIn3Te5 single-crystal properties and micro-Raman and infrared spectroscopies

The topography and roughness evolution of surfaces etched by laser-induced backside wet etching (LIBWE) is investigated in detail. The etching of sub-m gratings with a period of 760 nm into flat surfaces by means of interfering laser beams shows a saturation of the grating depth within 20 pulses. The over-etching of already microstructured surfaces results in the change of the cross section and in reduction of the microstructure height with increasing pulse number. The decrease in height of sub-micron gratings from 125 to less than 10 nm within 15 laser pulses causes a substantial roughness reduction. The depth limitations in etching of the gratings as well as the height reduction of microstructures are the result of the influence of the surface topography to the heat flow. The more efficient heating of surface peaks in contrast to the valleys results in higher etch rates and probably causes the smooth surfaces observed in LIBWE processing. The thermal diffusion length determines the structure dimension influenced by this smoothing effect. PACS 81.65.Cf; 81.05.Je; 42.70.Ce; 42.55.Lt     

Fast optical recording in dye-doped liquid crystals

Light-induced director reorientation in dye-doped nematic liquid crystals was recently reported to be an efficient method of writing permanent holographic gratings with high sensitivity [Phys. Rev. Lett. 82, 1855 (1999)]. We report the achievement of stable director reorientation in the same materials by means of a single 4-ns pulse of the second harmonic of a Nd:YAG laser. Fast recording of high-resolution holographic gratings (more than 500 lines/mm) can be obtained with an energy density as low as 7x10(-3)J /cm(2) .     

Fabrication of 550 nm gratings in fused silica by laser induced backside wet etching technique

A series of 550 nm spacing gratings were fabricated in fused silica by laser induced backside wet etching (LIBWE) method using the fourth harmonic of a Q-switched Nd:YAG laser (wavelength: λ = 266 nm; pulse duration: FWHM = 10 ns). During these experiments we used a traditional two-beam interference method: the spatially filtered laser beam was split into two parts, which were interfered at a certain incident angle (2θ = 28°) on the backside surface of the fused silica plate contacting with the liquid absorber (saturated solution of naphthalene-methyl-methacrylate c = 1.85 mol/dm³). We studied the dependence of the quality and the modulation depth of the prepared gratings on the applied laser fluence and the number of laser pulses. The surface of the etched gratings was characterized by atomic force microscope (AFM). The maximum modulation depth was found to be 180-200 nm. Our results proved that the LIBWE procedure is suitable for production of submicrometer sized structures in transparent materials.     

基于AgI2-缔合微粒共振散射效应测定阳离子表面活性剂

在pH 3.5 NaAc-HCl介质中,Ag 与过量的I-形成可溶性AgOI2-;当十六烷基三甲基溴化铵(CT-MAB)与AgI2-共存时形成粒径为700 nm的(CTMA-AgI2)n缔合微粒,在360 nm处产生一个共振散射峰,在470 m处产生一同步散射峰.CTMAB浓度cCTMAB在2.0～50.0×10-7mol·L-1范围内与散射光强度I360nm呈线性关系,回归方程为I360nm=2.03×107 cCTMAB 0.48,相关系数r为0.998 5,检出限为8.0×10-8mol·L-1.据此建立了一个测定阳离子表面活性剂含量的共振散射光谱法,用于水样分析,结果满意.共振散射光谱和激光散射研究表明,CTMAB 与AgI2-可通过静电力形成疏水性的CTMA-AgI2缔合物分子,该缔合物分子自动聚集形成稳定的(CTMA-AgI2)n缔合微粒.由于该缔合微粒仅在360 nm处产生共振散射效应,故体系呈乳白色.     

Spectroscopy and continuous-wave diode-pumped laser action of Yb3+:YVO4

The growth, spectroscopic properties, and laser performance of Yb:YVO4 crystal with laser diode pumping are reported. A peak absorption cross section of 7.4 x 10(-20) cm2 at 985 nm, a radiative lifetime of 0.25 ms, and a stimulated-emission cross section of 1.25 x 10(-20) cm2 at 1008 nm for pi polarization were determined for the Yb3+ ions in YVO4. Continuous-wave laser action of Yb:YVO4 at 1020-1027 nm was demonstrated with an output power of 610 mW and a slope efficiency of 49%.     

Electronic mechanism for refractive-index changes in intensively pumped Yb:YAG laser crystals

Refractive-index changes accompanying changes in population of electronic levels of Yb3+ ions in a Yb:YAG laser disk under intense diode and laser pumping have been studied by use of both a highly sensitive polarization interferometer and transient grating testing at 633 nm. The electronic change of the index that is due to excitation of the Yb3+ ions (which have different polarizability of ground state 2F7/2 and excited level 2F5/2) is strongly predominant over the thermal component. The polarizability differences are deltap (1.9 +/- 0.8) x 10(-26) and (1.95 +/- 0.25) x 10(-26) cm3 as measured at 633 nm in interferometric and transient grating experiments, respectively.     

Continuous-wave laser operation of Yb:LuVO4

We report on the room-temperature spectroscopic properties and continuous-wave laser operation of a new Yb:LuVO4 crystal. The peak absorption cross section for the pi-polarization is 8.42 x 10(-20) cm2 at 985 nm, and the stimulated emission cross section at 1020 nm is 1.03 x 10(-20) cm2. An output power of 0.36 W at 1041 nm was obtained with a slope efficiency of 47% by use of Ti:sapphire laser pumping. With diode pumping the output power reached 1.05 W at the highest available incident pump power of 6.8 W.     

Holographic reflection gratings in azobenzene polymers

Writing and reading of reflection gratings in films of an azo side-group polymer are reported. The gratings were induced holographically by use of an argon-ion laser at 488 nm. The measured diffraction efficiency was in the range 2-10%. To estimate the scattering of the reflected light within the material, we further characterized the gratings by calculating a characteristic transmission. A distinct minimum for this transmission was observed, which was redshifted farther from the writing wavelength for gratings written in 50-microm polymer samples.     

低强度激光辐照HeLa细胞诱导增殖效应的可见光谱特性

比较研究了可见波段405,514,633和785nm低强度激光辐照HeLa细胞的促增殖效应。实验采用100和1 000J.m-2两种有效能量密度的可见光波辐照细胞,照射后24,48,72h采用MTT法检测细胞活性。结果表明,405,633,785nm激光均能促进HeLa细胞增殖,且呈波长和时间依赖性;633nm激光辐照对细胞促增殖效应最显著;514nm激光辐照对HeLa细胞促增殖效应较不明显。不同光剂量对细胞增殖效应不同,405,633,785nm激光辐照时能量密度为1 000J.m-2的辐照组细胞增殖均较100J.m-2辐照组明显,而514nm激光辐照时1 000J.m-2辐照组与100J.m-2辐照组细胞增殖的差异不明显。     

Sudan IV dye based poly(alkyloxymethacrylate) films for optical data storage

The polymer poly{1-[2′-methyl-4′-(2″-methylphenylazo) phenylazo]-2-(m-methacryloyloxyoctyloxy}naphthalene, where m = 6, 8, 10, is synthesized by free radical addition polymerization method for holographic optical data storage. Characterization of the polymers is done by formation of the holographic grating. A study of the dependence of diffraction efficiency of the grating formed on various parameters is presented. Surface relief gratings on these polymer films are created upon exposure to argon ion laser beams at 514.5 nm without any subsequent processing steps. The surface structure of the relief gratings has been investigated by atomic force microscopy. The depth of surface relief in a typical case is found to be around 40 nm.     

Fabrication of a novel silica PLC hybrid integrated triplexer

<正>A new-style silica planar lightwave circuit(PLC) hybrid integrated triplexer,which can demultiplex 1490- nm download data and 1550-nm download analog signals,as well as transmit 1310-nm upload data,is presented.It combines SiO_2 arrayed waveguide gratings(AWGs) with integrated photodetectors(PDs) and a high performance laser diode(LD).The SiO_2 AWGs realize the three-wavelength coarse wavelength-division multiplexing(CWDM).The crosstalk is less than - 40 dB between the 1490- and 1550-nm channels, and less than - 45 dB between 1310- and 1490- or 1550-nm channels.For the static performances of the integrated triplexer,its upload output power is 0.4 mW,and the download output photo-generated current is 76μA.In the small-signal measurement,the upstream -3-dB bandwidth of the triplexer is 4 GHz,while the downstream -3-dB bandwidths of both the analog and digital sections reach 1.9 GHz.     

十二烷基硫酸钠(SDS)增强若丹明6G水溶液激光激发荧光谱研究

报道了若丹明6G水溶液添加不同浓度的表面活性剂十二烷基硫酸钠(SDS)时激光激发染料的变化,发现较低的掺入量导致R6G荧光减弱,适量SDS的加入使荧光增强,在5×10-5 mol·L-1的R6G水溶液中,加入6×10-2 mol·L-1 SDS,荧光增强因子达到3.1。当R6G浓度为1×10-4 mol·L-1时,加入2×10-2 mol·L-1,染料激光阈值显著降低。测量了不同浓度的R6G溶液的吸收光谱及加入不同浓度SDS后的荧光谱,分析了不同SDS加入量下R6G荧光减弱及增强的物理机制。     

Petawatt laser pulses

We have developed a hybrid Ti:sapphire-Nd:glass laser system that produces more than 1500 TW (1.5 PW) of peak power. The system produces 660 J of power in a compressed 440+/-20 fs pulse by use of 94-cm master diffraction gratings. Focusing to an irradiance of >7x10(20) W/cm (2) is achieved by use of a Cassegrainian focusing system employing a plasma mirror.     

Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating

We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17).     

Femtosecond holography in lithium niobate crystals

Spatial gratings are recorded holographically by two femtosecond pump pulses at 388 nm in lithium niobate (LiNbO3) crystals and read out by a Bragg-matched, temporally delayed probe pulse at 776 nm. We claim, to our knowledge, the first holographic pump-probe experiments with subpicosecond temporal resolution for LiNbO3. An instantaneous grating that is due mostly to the Kerr effect as well as a long-lasting grating that results mainly from the absorption caused by photoexcited carriers was observed. The Kerr coefficient of LiNbO3 for our experimental conditions, i.e., pumped and probed at different wavelengths, was approximately 1.0 x 10(-5) cm2/GW.