Generation of 320 fs pulses with a distributed feedback dye laser

A new achromatic distributed feedback dye laser (DFDL) arrangement is described. The experimental conditions for subpicosecond pulse generation with the new device were investigated. For the first time, stable generation of subpicosecond pulses (350 fs) at 616 nm was achieved with a DFDL. The simultaneous spectral and autocorrelation measurements showed that the amplified DFDL pulses are nearly transform limited, having a pulse form close to the sech² shape.     

周期量级超短激光脉冲在近临界密度等离子体中形成的光孤子

利用一维粒子模拟程序，观测到周期量级的超短激光脉冲在等离子体中可以以孤子形式传播.它在一定密度等离子体中以较高的群速度向前传播，并在到达等离子体与真空界面时发生反射和透射.当入射激光脉冲强度增大时，非线性调制效应使它产生较大的频率下移，致使光孤子传播速度变小.另外，对于同样光强下的几十个周期以上的光脉冲，它在等离子体中传播时形成的则是一连串低频的被捕获在等离子体中的光孤子. 关键词： 光孤子 超短激光脉冲 等离子体 粒子模拟     

Generation of 49 fs pulses in a CPM laser pumped by a small-frame Ar+ laser

A colliding pulse mode-locked ring dye laser, pumped by an all-line small frame Ar⁺ laser has been used to generate stable pulses as short as 49 fs with pulse duration and stability similar to those obtained with the usual configuration where a single line of the pump is used. The effects of cavity alignment on the absorber saturation are presented and explained in terms of an analysis of stability of the ring cavity.     

Generation of pulses shorter than 70 fs with a synchronously-pumped CW dye laser

Pulses shorter than 70 fs are generated with a synchronously-pumped cw dye laser using a dye medium composed of a mixture of rhodamine 6G and a fast recovery saturable absorber, DQOCI. The laser pulses exhibit no satellites. A stable output of 30 mW is obtained for only 300 mW of pump power.     

Observation of superradiant amplification of ultrashort laser pulses in a plasma

We demonstrate the amplification of a femtosecond signal pulse in an underdense plasma by a novel mechanism called superradiant amplification. The pulse is amplified by a counterpropagating few picosecond long pump pulse. In the superradiant regime, the ponderomotive forces exceed the electrostatic forces and arrange the plasma electrons to reflect the pump light into the signal pulse. We found a significant amplification in energy and intensity. The time structure of the amplified signal pulse carries intrinsic features of the superradiant regime. Sub-10-fs pulses of petawatt power appear feasible.     

Generation of fs laser pulses from a ps pulse-pumped optical parametric amplifier with a beat-wave seed signal

We describe a method of ultrashort-pulse and ultrafast-pulse-train generation through optical parametric amplification of a laser beat wave. Numerical simulation shows that 250-fs laser pulses at 1.55 μm are generated from a beat-wave seeded optical parametric amplifier pumped by a 30-ps laser at 1064 nm. The pulse compression is attributable to sideband generation and parametric amplification under group velocity mismatch. Our experimental result confirms efficient generation of comb-like sidebands for the mixing waves from such an optical parametric amplifier.     

Generation of long plasma channels in air by focusing ultrashort laser pulses with an axicon

We show that by focusing ultrashort-pulsed laser beams in air with an axicon, relatively long plasma channels can be generated. The axicon generates Bessel-like beams, where the on-axis intensity stays high over distances much longer compared to focusing with conventional lenses. We developed a scheme to detect the presence of the plasma, based on its screening property. Using this scheme, we detected plasma channels longer than 1 m and 3.5 m generated by 8 mJ and 90 mJ input pulse energies, respectively. Our simulations show that axicon focusing can yield self-guided propagation with or without contribution of plasma, depending on the input pulse power.     

Formation of ultrashort electron pulses on scattering of an electron beam by a standing laser wave of ultrashort duration

The scattering of a well collimated electron beam by a strong standing laser wave of ultrashort duration, giving rise to a great number of scattered photons, is considered. This type of scattering is found to cause an electron beam to divide effectively into two parts. Ultrashort laser pulses are shown to be capable of forming ultrashort electron bunches whose length is governed by the laser beam diameter.     

YAG激光同步泵浦染料激光器产生38fs光脉冲

研究表明,不用碰撞脉冲锁模技术,而由一台简单的线型腔染料激光器,就可成功地产生短达38飞秒的光脉冲。这种激光器用六镜折叠腔,其中有Rh6G和DOPCI两个喷流和一个棱镜对色散补偿器,用连续锁模Nd:YAG激光器的倍频输出同步泵浦。染料激光脉冲的平均功率为20mW,脉冲重复频率近100MHz。     

Measurement of ultrashort laser pulses

A proposal for measuring the pulse shape of ultrashort laser pulses is described. The proposed method consists of a Gamo triple intensity-interferometer to measure the triple-correlation function of the light pulses. A subsequent signal processing algorithm is used to reconstruct the true shape of the light pulses out of their triple-correlation function. The suggested method is quite insensitive to noise, as shown by means of computer simulations.     

Conical emission from laser plasma interactions in the filamentation of powerful ultrashort laser pulses in air

We performed detailed experimental and numerical investigations of the conical emission (CE) accompanying the filamentation of powerful ultrashort laser pulses in air. It was found that the CE originates from self-phase modulation in the plasma produced by the pulse during propagation. The experiment and the simulation agree on the essential features of the CE: The CE angle decreases with increasing wavelength and is independent of the position along the filament, and there is no CE at Stokes-shifted wavelengths.     

Thomson scattering from ultrashort and ultraintense laser pulses

The Thomson scattering in an ultraintense ( approximately 10(18) W cm(-2)) and ultrashort (20 fs) laser field is calculated that demonstrates different characteristics from those of the low-intensity field case. The electron trajectory no longer conforms to a figure-eight pattern, and the spectra demonstrate complex shifting and broadening to suggest that Thomson scattering can be used for characterizing pulsed lasers. The initial phase at the electron entrance of the field can critically affect the Thomson scattering, but its effect is weighted by the intensity profile of the field. As a result, the fourfold symmetry of the radiation pattern breaks down when the electron enters the field closer to the pulse peak. The relationship between the Thomson scattering and Compton scattering in the high field is analyzed.     

Vortices in ultrashort laser pulses

The propagation of optical vortices nested in broadband femtosecond laser beams was studied both numerically and experimentally. Based on the nonlinear Schrödinger equation, the dynamics of different multiple-vortex configurations with varying topological charge were modelled in self-focussing and self-defocussing Kerr media. We find a similar behavior in both cases regarding the vortex–vortex interaction. However, the collapsing background beam alters the propagation for a positive nonlinearity. Regimes of regular and possibly stable multiple filamentation were identified this way. Experiments include measurements on pairs of filaments generated in a vortex beam on an astigmatic Gaussian background with argon gas as the nonlinear medium. Spectral broadening of these filaments leads to a supercontinuum which spans from the visible range into the infrared. Recompression yields <19 fs pulses. Further optimization may lead to much better recompression.     

Generation of synchronised ultrashort pulses using a dual wavelength synchronously mode-locked CW dye laser

The properties of a dual wavelength synchronously mode-locked cw dye laser are described. Results are presented which show that good mode-locking is obtainable under dual wavelength conditions. Cross-correlation measurements indicate that the time separation of the pulses depends on gain saturation within the dye.     

Microablation with ultrashort laser pulses

This paper reports the micromachining results of different materials (Al, Si, InP and fused silica) using a Ti : sapphire laser at the wavelength of 800 and 267 nm with variable pulse lengths in the range from 100 fs to 10 ps. The hole arrays with a diameter up to a few μm through microdrilling are presented. We discussed how an effective suppression of the thermal diffusion inside the ablated materials and an effective microablation could be realized. If the laser fluence is taken only slightly above the threshold, a hole array can be drilled with diameters even smaller than the wavelength of the laser. Some examples are presented in the paper.     

Amplification of ultrashort laser pulses by a resonant Raman scheme in a gas-jet plasma

Raman amplification of subpicosecond laser pulses up to 95 times is demonstrated at corresponding frequencies in a gas-jet plasma. The larger amplification is accompanied by a broader bandwidth and shorter pulse duration. Theoretical simulations show a qualitative agreement with the measurements, and the effects of the plasma conditions and laser intensities are discussed.     

镱钠共掺氟化钙锁模激光器产生190 fs光脉冲

在半导体激光器高功率抽运的镱、钠共掺氟化钙(Yb, Na:CaF₂)激光器中, 通过对晶体的负热透镜效应的数值模拟,进行激光器腔型的调节和优化,使得该激光器在采用2%的耦合输出镜和吸收抽运功率为7.8 W的条件下,获得了脉冲宽度为190 fs、平均输出功率为503 mW、中心波长为1034 nm、重复频率为82.4 MHz的连续锁模脉冲序列. 如果计算晶体表面反射等其他形式的泄漏输出,激光器的总平均输出功率为905 mW. 关键词： Yb 2晶体')" href="#">Na:CaF₂晶体 激光二极管抽运 飞秒激光     

Multiphoton electron emission processes induced by different kinds of ultrashort laser pulses

Using ultrashort laser pulses of regular (gaussian shaped) time and spectral distribution, theoretically predicted, multiphoton electron emission processes have been observed. On changing this regular form of the ultrashort light pulses, however, the character of the emission process also changes, the explanation of which follows only partly from the evolution of the mode-locking train.