Amplification of fluorescence using collinear picosecond optical parametric amplification at degeneracy

We demonstrate the output characteristic of broadband parametric amplification of incoherent light pulses in a 355-nm pumped degenerate picosecond optical parametric amplification with either saturated or unsaturated amplification.The optical parametric amplifier is seeded by the fluorescence generated in a solution of pyridine-1 dye in ethanol.With the saturated amplification,we can obtain high energy incoherent light pulses,whose full width at half maximum bandwidth varies from 16 nm to 53 nm for the different phase matching angles near degeneracy.Moreover,the unsaturated bandwidth of the amplified pulses fits well to the calculated result at degeneracy.Selecting s-polarized fluorescence with a Glan-Taylor prism,the maximum bandwidth of the amplified fluorescence is found to be 59 nm for a purely s-polarized seed.The maximum output energy is 0.67 mJ for the optical parametric amplifier.By using an optical filter and compressor,the generated high energy incoherent light has great potential as the incoherent pump,signal or idler wave of a parametric down-conversion process,so that a wave with a high degree of coherence can be generated from an incoherent pump light.     

Enhancement of Gain in L-Band Bismuth-Based Erbium-Doped Fibre Amplifier Using an Un-pumped EDF and Midway Isolator

A hybrid L-band erbium-doped fibre amplifier (EDFA) with enhanced gain characteristic is demonstrated without a significant noise figure penalty. It uses a backward C-band amplified stimulated emission from both the ends of a bismuth-based EDFA system to pump an unpumped erbium-doped fibre (EDF) for gain enhancing. The maximum gain enhancement of 4.0dB is obtained at wavelength 1604nm with EDF length of 20m. The gain spectrum is reasonably fiat in this amplifier compared with the amplifier without an EDF. The gain varies from 27.4 dB to 30.2 dB at wavelength region 1564-1608 nm with incorporation of 20 m EDF. Noise figure also varies from 6.0 to 7.TdB at this wavelength region.     

Millijoule pulse energy picosecond fiber chirped-pulse amplification system

The efficient generation of a 1.17-mJ laser pulse with 360 ps duration using an ytterbium (Yb)-doped fiber amplifier chain seeded by a homemade mode-locked fiber laser is demonstrated experimentally.A specially designed figure-of-eight fiber laser acts as the seed source of a chirped-pulse amplification (CPA) system and generates mode-locked pulses with hundreds of picosecond widths.Two kinds of large-mode-area (LMA) double-clad Yb-doped fibers are employed to construct the pre-amplifier and main amplifier.All of the adopted instruments help avoid severe nonlinearity in fibers to raise sub-nanosecond pulse energy with acceptable signal-to-noise ratio (SNR).The output spectrum of this fiber-based CPA system shows that amplified spontaneous emission (ASE) is suppressed to better than 30 dB,and the onset of stimulated Raman scattering is excluded.     

Anisotropic stimulated emission cross-section measurement in Nd:YVO_4

As a crucial parameter in the design and analysis of laser performances, stimulated emission(SE) cross-section is currently considered to be dependent on several factors, such as temperatures and eigen-polarizations for anisotropic crystals. In contrast with these factors, impact of propagating directions upon SE cross-section has garnered less attention.In this paper, to investigate the SE cross-section in arbitrary propagating directions, fluorescence spectra for the transition ~4F_(3/2)→~4I_(11/2) in Nd:YVO_4 are measured in different propagating directions. Based on Fuchtbauer–Ladenburg equation model, the propagating direction-dependent SE cross-section spectra in Nd:YVO_4 are obtained for the first time, to our best knowledge. A novel concept of anisotropic SE cross-section is proposed to interpret the propagating direction-dependent effect. The experiment results reveal that for an arbitrary propagating direction the SE cross-section of e light around 1064 nm can be expressed as a superposition from two principle axial propagating directions with a weight of plane projection.     

Generation of a compact high-power high-efficiency normal-dispersion pumping supercontinuum in silica photonic crystal fiber pumped with a 1064-nm picosecond pulse

Broadband normal dispersion pumping supercontinuum （SC） generation in silica photonic crystal fiber （PCF） is investigated in this paper. A 1064-nm picosecond fiber laser is used to pump silica PCF for the SC generation. The length of PCF is optimized for the most efficient stimulated Raman scattering process in the picosecond pump pulse region. The first stimulated Raman Stokes peak is located in the anomalous dispersion regime of the PCF and near the zero dispersion wavelength; thus the SC generation process can benefit from both a normal dispersion pumping scheme and an anomalous dispersion pumping scheme. The 51.7-W SC spanning from about 700 nm to beyond 1700 nm is generated with an all-fiber configuration, and the pump-to-SC conversion efficiency is up to 90%. In order to avoid the output fiber end face damage and increase the stability of the system, an improved output solution for the high power SC is proposed in our experiment. This high-efficiency near-infrared SC source is very suitable for applications in which average output power and spectral power density are firstly desirable.     

Effects of temperature and input energy on quasi-three-level emission cross section of Nd3+:YAG pumped by flashlamp

The influence of temperature and input energy on fluorescence emission cross section of Nd³⁺:YAG crystal is studied. The stimulated emission cross sections of quasi-three-level systems are determined in a temperature range from -30 to 60 ℃ and an input energy range from 18 to 75 J. The cross section is found to decrease with the temperature and the input energy is increased. This is attributed to the thermal broadening mechanism of the emission line. This study is relevant for the development of laser design.     

122-W high-power single-frequency MOPA fiber laser in all-fiber format

We demonstrate a high-power single-frequency master oscillator power amplifier (MOPA) fiber laser.The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm,with a linewidth narrower than 20 kHz and output power of 120 mW.By using two-stage amplification,a single-frequency fiber laser with an output power of 122 W is obtained,and the optical-optical conversion efficiency is 72%.No significant amplified spontaneous emission (ASE) or stimulated Brillouin scattering (SBS) is observed.The output power can be further increased by launching more pump power.     

Fluorescence spectrum,thermal properties,and continuous-wave laser performance of the mixed crystal Nd：Lu0.99La0.01 VO4

The fluorescence spectrum and thermal properties of the mixed crystal Nd：Luo.gvLa~.o1VO4 are determined. The strongest emission peak located at 1065.6 nm had a full width at half maximum （FWHM） of 2.1 nm. Continuous-wave （CW） laser performance is demonstrated by a compact planar planar cavity that is end- pumped by a diode laser. The laser output characteristics are investigated by using output couplers with different transmissions. A maximum CW output power of 8.09 W was obtained at an incident pump power of 19.4 W, which corresponds to an optical-to-optical conversion efficiency of 41.7% and a slope efficiency of 54.6%. The dependence of optimum transmission on pump power is calculated theoretically and is found to be consistent with experimental results.     

90.4-W all-fiber single-frequency polarization-maintained 1083-nm MOPA laser employing ring-cavity single-frequency seed oscillator

A high-power all-fiber single-frequency polarization-maintained（PM）laser operating at 1 083 nm is demonstrated using a master oscillator power amplifier（MOPA）structure.The seed source of this MOPA laser system is an in-house-built ring-cavity fiber oscillator.Four-stage amplification configuration is employed, in which the maximal output power of the main amplifier is 90.4 W,corresponding to a conversion efficiency of 72.5%.The polarization extinction ratio of the output light is 13 dB.The amplified spontaneous emission is suppressed by a factor of over 25 dB,and no stimulated Brillouin scattering effect is observed when a large-mode-area and high absorption coefficient PM gain fiber is employed.     

Anomalously Strong Scattering of Spontaneously Produced Laser Radiation in the First Free-Electron Laser and Study of Free-Electron Two-Quantum Stark Lasing in an Electric Wiggler with Quantum-Wiggler Electrodynamics

We calculate the scattering cross section of an electron with respect to the spontaneously produced laser radiation in the first free-electron laser （FEL） with quantum-wiggler electrodynamics （QWD）. The cross section is 1016 times the Thomson cross section, confirming the result obtained by a previous analysis of the experimental data. A QWD calculation show that spontaneous emission in an FEL using only an electric wiggler can be very strong while amplification through net stimulated emission is practically negligible.     

Er~(3+)/Yb~(3+) codoped phosphate glass laser end-pumped by laser diode

An Er3 /Yb3 phosphate laser glass was fabricated and characterized. According to McCumber theory, the stimulated emission cross-section of Er3 ions at 1533 nm calculated by absorption spectrum was 0.84×10-20 cm2, and the fluorescence lifetime of 4I13/2 level was 8.5 ms. Continuous wave (CW) laser operation of this Er3 /Yb3 phosphate glass pumped by laser diode (LD) was demonstrated at room temperature. The maximum output power of 80 mW and slope efficiency of 16.5% were obtained.     

Probing the strange quark condensate by di-electrons from φ-meson decays in heavy-ion collisions at SIS energies

QCD sum rules predict that the change of the strange quark condensate 〈ˉss〉 in hadron matter at finite baryon density causes a shift of the peak position of the di-electron spectra from φ-meson decays. Due to the expansion of hadron matter in heavy-ion collisions, the φ peak suffers a smearing governed by the interval of density in the expanding fireball, which appears as an effective broadening of the di-electron spectrum in the φ region. The emerging broadening is sensitive to the in-medium change of 〈ˉss〉. This allows to probe directly in-medium modifications of 〈ˉss〉 via di-electron spectra in heavy-ion collisions at SIS energies with HADES. Received: 22 November 2002 / Accepted: 30 January 2003 / Published online: 29 April 2003     

Analysis of directional emission in square resonator lasers with an output waveguide

Square microcavity laser with an output wavegnide is proposed and analyzed by the finite-difference time-domain(FDTD)technique.For a square resonator with refractive index of 3.2,side length of 4μm,and output wavegnide of 0.4-μm width,we have got the quality factors(Q factors)of 6.7×10~2 and 7.3×10~3 for the fundamental and first-order transverse magnetic(TM)mode near the wavelength of 1.5μm,respectively.The simulated intensity distribution for the first-order TM mode shows that the coupling efficiency in the waveguide reaches 53%.The numerical simulation shows that the first-order transverse modes have fairly high Q factor and high coupling efficiency to the output waveguide.Therefore the square resonator with an output wavegnide is a promising candidate to realize single-mode directional emission microcavity lasers.     

An 88-nm broadband ASE source with bismuth-based erbium-doped fiber

A broadband amplified spontaneous emission (ASE) source of 88 nm is demonstrated using novel bismuthbased erbium-doped fiber (EDF) with the length of only 49.2 cm in a bi-direction pumping scheme. The maximum output power of 14.3 dBm is obtained under total pump power of 162 mW. The fiber loop mirror which works as a broadband reflector is responsible for the broadband output spectrum of this source according to the experiments.     

Zebrafish imaging and two-photon fluorescence imaging using ZnSe quantum dots

This study is to report a ZnSe quantum dot with a large two-photon absorption cross section and good biocompatibility,which can be used in bioimaging.Fluorescence emission at 410 nm is observed in the quantum dot under 760-nm laser excitation.These biocompatible quantum dots exhibit a two-photon cross-section of 9.1×10~5 GM(1 GM=10~(-50) cm~4·s/photon).Two-photon excited laser scanning microscopic images show that cells co-cultured with ZnSe quantum dots are found in the blue channel at a fluorescence intensity that is 14.5 times that of control cells not cocultured with quantum dots.After incubating zebrafish larvae with ZnSe quantum dots for 24 h,the fluorescence intensity of the yolk sac stimulated by ultraviolet light is 2.9 times that of the control group.The proposed material shows a great potential application in biological imaging.     

2277-W continuous-wave diode-pumped heat capacity laser

A high power continuous-wave (CW) diode-pumped Nd:YAG laser operated in heat capacity mode is demonstrated by use of two identical highly efficient diode-pumped laser heads placed in a plane-plane resonator.The laser heads are uniformly pumped with a five-fold symmetrical side-pumping configuration, and each head is able to output maximum output power of 2200 W at 808 nm.Under a total pump power of 4290 W,the output power of the laser at 1064 nm is up to 2277 W,corresponding to an optical-to-optical efficiency of 53.1%.     

Spectral analysis of short-wavelength emission by up-conversion in a Tm~(3+):ZBLAN dual-diode-pumped optical fiber

The fluorescence evolution along Tm3+-doped Zr F4–Ba F2–La F3–Al F3–Na F(ZBLAN) optical fibers, as well as amplified spontaneous emission in the UV-IR region with emphasis on 350 nm, 365 nm, and 450 nm, is studied,estimating optimal fiber lengths for amplification within the region. The fibers were diode-pumped with single and double lines(687 and/or 645 nm). Double-line pumping presents a quite superior efficiency for producing UV-blue signals with the benefit of requiring very short fibers, around 20 cm, compared to single-line pumping requiring more than 50 cm. A virtual cycle in which the pumps enhance each other's absorption is the key to these systems.     

Er3+/Yb3+ codoped phosphate glass laser end-pumped by laser diode

An Er3+/yb3+ phosphate laser glass was fabricated and characterized. According to McCumber theory, the stimulated emission cross-section of Er3+ ions at 1533 nm calculated by absorption spectrum was 0.84 × 10-20 cm2, and the fluorescence lifetime of 4I13/2 level was 8.5 ms. Continuous wave (CW) laser operation of this Er3+/Yb3+ phosphate glass pumped by laser diode (LD) was demonstrated at room temperature. The maximum output power of 80 mW and slope efficiency of 16.5% were obtained.     

A 168-W high-power single-frequency amplifier in an all-fiber configuration

We present a high-power,single-frequency,narrow linewidth fiber amplifier based on master oscillator power amplification chains in an all-fiber configuration.The effect of the delivery fiber on the maximum output power is studied.A home-made 1064-nm seed laser with a 20-kHz linewidth is boosted to 129 W,and limited by stimulated Brillouin scattering(SBS) when the delivery fiber is 1.2 m long.By shortening the delivery fiber length to 0.7 m,the SBS threshold is increased efficiently and the maximum output power rises to 168 W with an 82.9% power conversion efficiency.The experimental results indicate that the output power can be further raised by shortening the delivery fiber length and increasing the pump power.     

Stimulated Emission from a TiO2 Particle-Dispersed Dye Polymer Plane Waveguide

We report the stimulated emission from a dye doped polymer plane waveguide with TiO2 particles. This waveguide consists of a poly （methylmethacrylate） （PMMA） film containing laser dye DCM as a gain medium. The emission spectrum of the film pumped by the Nd：YAG laser is different from the amplified spontaneous emission of the dye-doped film without particles. It is shown that when the excitation intensity reaches the threshold 9.6 μJ, the broad band emission spectrum narrows into multiple separate peaks with central wavelength of 608 nm. The linewidth of the sharp peak is 0.5 nm. According to our analyses, this phenomenon is due to the multiscattering of the disordered TiO2 particles inside the gain polymer film.