Short-pulse, all-fiber, Raman laser with dispersion compensation in a holey fiber

The use of Raman gain in conventional fiber followed by dispersion compensation in a holey fiber in a synchronously pumped laser configuration allowed compression by a factor of 8.5 of output pulses at a selected wavelength with respect to the pump pulses. We obtained 2-ps output pulses at 1.14 microm from a totally fiber-integrated laser pumped with 17-ps pulses at 1 microm. Higher pulse compression should be possible with nonlinear chirp compensation. Ultrashort-pulse, all-fiber Raman lasers at wavelengths shorter than 1.3 microm are feasible.     

Solitonic all-optical switch based on the fractional Talbot effect

A periodic pattern of hundreds of beams is shifted by half its transverse period as the result of excitation of parametric spatial solitons and the fractional Talbot effect. The all-optical switch that is obtained operates with 1-ps pulses.     

Compression of ultraintense laser pulses in inhomogeneous plasma upon backward stimulated raman scattering

The potential for time compression of ultraintense laser pulses in plasma based on nonlinear interactions between waves during backward stimulated Raman scattering is analyzed analytically and numerically. The optimal conditions for obtaining a maximal energy conversion coefficient of 10-ps laser pulses to the energy of 100-fs Stokes pulses are found.     

40-GHz pulse-train generation at 1.5 mum with a chirped fiber grating as a frequency multiplier

Pulse-train multiplication based on the temporal Talbot effect in a linearly chirped fiber Bragg grating has been experimentally demonstrated. A 40-GHz repetition-rate, nearly transform-limited 10-ps duration optical pulse train at 1.533 mum has been obtained from a 2.5-GHz mode-locked Er- Yb:glass laser by use of a 100-cm-long linearly chirped apodized fiber grating.     

White-light supercontinuum generation with 60-ps pump pulses in a photonic crystal fiber

The generation of a spatially single-mode white-light supercontinuum has been observed in a photonic crystal fiber pumped with 60-ps pulses of subkilowatt peak power. The spectral broadening is identified as being due to the combined action of stimulated Raman scattering and parametric four-wave-mixing generation, with a negligible contribution from the self-phase modulation of the pump pulses. The experimental results are in good agreement with detailed numerical simulations. These findings demonstrate that ultrafast femtosecond pulses are not needed for efficient supercontinuum generation in photonic crystal fibers.     

150-ps pulse Raman generator pumped by a 1-kHz sub-nanosecond passively Q-switched laser system

Raman conversion with a single Ba(NO₃)₂ crystal (barium nitrate) either in single- and double-pass travelling-wave setups has been investigated. A Master-Oscillator-Power-Amplifier (MOPA) system, based on a passively Q-switched (PQS) laser generating 500-ps pulses and delivering a total energy of 350 μJ at 1 kHz, was used as pump source for the Raman generator. The two-passes setup yielded 116-μJ, 150-ps Fourier- and diffraction-limited pulses at 1198 nm for ≈3× the Raman threshold with no additional Stokes lines, and conversion efficiency of 35%. Such results are interesting not only for direct applications of the wavelength-shifted laser source, but also for further pulse-compression and supercontinuum generation in fibers. Indeed, self-phase modulation up to 0.82 nm has been demonstrated (pulse compression down to 5 ps) as well as 120-nm supercontinuum.     

High-average-power picosecond Yb-doped fiber amplifier

We report on a cladding-pumped, ytterbium-doped large-core-area fiber amplifier that is capable of generating 51.2 W of average power at a 1064-nm center wavelength, an 80-MHz repetition rate, and a 10-ps pulse duration. In an ytterbium-doped large-mode-area fiber these pulses could be amplified up to 43.2 W with diffraction-limited beam quality (M(2)~1.3) . Power scaling limitations that arise from nonlinear distortions such as self-phase modulation and stimulated Raman scattering are discussed.     

20-kW peak power all-fiber 1.57-microm source based on compression in air-core photonic bandgap fiber, its frequency doubling, and broadband generation from 430 to 1450 nm

We demonstrate an ultrashort all-fiber-integrated chirped-pulse amplification system yielding 1-ps pulses with 20 kW of peak power. 40-ps initial pulses generated by an externally modulated laser diode are chirped by self-phase modulation in a conventional fiber, amplified, and compressed in 110 m of air-core photonic bandgap fiber. The compressed pulses are frequency doubled in a periodically poled KTP crystal with up to 48% efficiency and applied to supercontinuum generation in a holey fiber, resulting in a high-power uniform continuum that stretches from 430 to 1450 nm.     

Generation of a 160-GHz transform-limited pedestal-free pulse train through multiwave mixing compression of a dual-frequency beat signal

We report the experimental generation of a 160-GHz picosecond pulse train at 1550 nm, using multiple four-wave mixing temporal compression of an initial dual-frequency beat signal in the anomalous-dispersion regime of a nonzero dispersion-shifted fiber. Complete intensity and phase characterizations of the pulse train were carried out by means of a frequency-resolved optical gating technique, showing that 1.27-ps transform-limited pedestal-free Gaussian pulses were generated.     

新型全光纤高能量飞秒光脉冲源的数值模拟

数值模拟了自相似脉冲的产生与压缩,得到一种产生高能量飞秒光脉冲的新方法.结果表明:利用掺铒光纤对光脉冲进行自相似传输,可得到含线性频率啁啾的高能量自相似光脉冲;自相似光脉冲经过空芯光子带隙光纤的一级线性压缩和高非线性光纤的二级非线性压缩,可获得高峰值功率的飞秒光脉冲;压缩过程中存在最佳光纤长度;喇曼自频移和自陡效应对脉冲压缩产生不利影响.     

All-optical square-pulse generation and multiplication at 1.5 mum by use of a novel class of fiber Bragg gratings

A new class of linearly chirped fiber Bragg gratings, suitable for all-fiber optical multiplication and reshaping of picosecond pulse trains, is proposed and experimentally demonstrated. Repetition-rate multiplication, based on the temporal Talbot effect, is achieved by accurate control of the grating chirp, and a suitable design of the index-modulation depth profile allows for simultaneous square-pulse shaping. A 50-ps squarelike optical pulse train at 10-GHz repetition rate is obtained, starting from a 2.5-GHz Gaussian pulse train emitted by a mode-locked Er-Yb laser.     

Dispersion-mode pulsed laser

A new self-consistency condition in pulsed lasers with strong intracavity dispersion imposes dispersion modes with specific cavity-length dependent pulse rates, utilizing pulse-train self-imaging properties of a temporal Talbot effect. We give an experimental demonstration of such a laser operation, using a long fiber cavity. We also demonstrate temporal Talbot imaging of a train of short pulses that propagate along large distances of dispersive fibers.     

Ultrawide tunable Er soliton fiber laser amplified in Yb-doped fiber

A Raman-shifted and frequency-doubled high-power Er-fiber soliton laser for seeding an efficient high-power Yb fiber femtosecond amplifier is demonstrated. The Raman-shifted and frequency-doubled Er-soliton laser is tunable from 1.00 to 1.070microm and produces bandwidth-limited 24-pJ pulses at a repetition rate of 50 MHz with a FWHM pulse width of 170 fs at 1.040microm . The Yb(3+) amplifier has a slope efficiency of 52% and generates 3-ps linearly chirped pulses with an average power of 0.8 W at 1.05microm . After pulse compression, 74-fs bandwidth-limited pulses with an average power of 0.4 W and a pulse energy of 8 nJ are generated.     

Pulsed degenerate optical parametric oscillator based on a nonlinear-fiber Sagnac interferometer

We report operation of an all-fiber degenerate optical parametric oscillator that employs a nonlinear-fiber Sagnac interferometer as a parametric amplifier. Synchronous pumping with 3.9-ps pulses at 1544 nm yields 0.83-ps output pulses. The wide bandwidth of the fiber parametric amplifier causes the oscillator to act as a pulse compressor. The output signal pulses exhibit improved spectral symmetry and a reduced time-bandwidth product compared with the pump pulses. Currently, the net group-velocity dispersion in the passive section of the fiber cavity limits the signal-pulse bandwidth and hence the minimum-obtainable pulse width. This experiment suggests the possibility of frequency conversion by operation of a similar pulsed parametric oscillator away from degeneracy.     

High-power picosecond fiber amplifier based on nonlinear spectral compression

We report on the rare-earth-doped fiber-based generation of nearly transform-limited 10-ps pulses based on self-phase-modulation-induced spectral compression. An ytterbium-doped low nonlinearity photonic crystal fiber is used as a gain medium. An average power of as much as 97 W at a repetition rate of 47 MHz, corresponding to a peak power as high as 200 kW, was obtained. Furthermore, efficient second-harmonic generation by application of this high-power laser source is discussed.     

色散缓变光纤中飞秒高阶孤子脉冲的增强压缩

提出了一种利用孤子绝热放大效应与高阶孤子脉冲压缩效应相结合来压缩飞秒高阶孤子的新方法.通过数值模拟方法证明,采用三阶色散为负的色散缓变光纤压缩高阶孤子,可利用喇曼散射效应与负三阶色散的相互作用,消除正三阶色散对光脉冲压缩产生的不利影响,增加压缩比,提高压缩后光脉冲的质量.研究表明,在色散缓变参量一定的情况下,孤子阶数越高,所需最佳光纤长度越短、光脉冲的压缩比越大;对于相同功率的孤子光脉冲,光脉冲的压缩比随着色散缓变参量的增大而增大;无论是孤子脉冲还是高斯脉冲都适合于色散缓变光纤中的高阶孤子脉冲压缩.     

Nonlinear second-harmonic pulse compression with tilted pulses

We demonstrate that the group velocities of interacting pulses can be adjusted by pulse tilting to optimize second-harmonic pulse compression for a variety of nonlinear crystals and wavelengths. As an experimental proof we present results of ninefold compression of 1.3-ps Nd:glass laser pulses in beta -barium borate crystal.     

Efficient subnanosecond diode-pumped passively Q-switched Nd:YVO4 self-stimulated Raman laser

Generation of efficient subnanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:YVO4/Cr4+:YAG laser is demonstrated. Experimental results reveal that self-frequency Raman conversion can be achieved with a c-cut Nd:YVO4 crystal in a nearly hemispherical cavity. At 2.0 W of incident pump power, the self-stimulated Raman laser produces stable 710-ps pulses at a Stokes wavelength of 1178.6 nm with 7.2 microJ of pulse energy at a 17-kHz repetition rate.     

超短脉冲激光照射下光栅Talbot效应的实验研究

理论上研究了超短脉冲激光照射下光栅的Talbot效应,得到了超短脉冲激光照射下光栅Talbot图像的性质.实验上采用严格的实验方法(频率分辨光学开关装置测量超短脉冲激光、反射式扩束系统对超短脉冲进行扩束)很好地验证了理论分析结果.理论分析和实验结果表明,超短脉冲激光照射下光栅的Talbot图像的对比度会显著下降,而且超短脉冲激光的脉宽越短,Talbot距离越大,Talbot图像的对比度会进一步下降.     

Wavelength-tunable high-power picosecond pulses from a fiber-pumped diode-seeded high-gain parametric amplifier

We describe a high-gain optical parametric amplifier (OPA) and optical parametric generator (OPG) system pumped by a fiber chirped-pulse amplification source based on novel large-mode-area fiber components. 45-nJ OPG thresholds and 34% pump-signal conversion efficiencies are obtained for ~4-ps pulses. OPA gains in excess of 75 dB and pump-signal conversion efficiencies of ~39% (external) are demonstrated. Furthermore, we show that injection seeding of such high-gain parametric devices by use of a low-power continuous-wave beam results in high-power (>18-kW) picosecond pulses with a time-bandwidth produce of ~0.65, some ten times less than from a free-running OPG. Using such an approach, we obtain 2.7-ps 50-nJ pulses at 1.310 mum .