High harmonic generation at 1 kHz repetition rate with a pulsed valve

High harmonic generation at 1 kHz repetition rate is reported. A piezoelectric pulsed valve together with a femtosecond Ti:Sapphire laser both operating at 1 kHz are employed to generate high harmonic radiation in xenon and argon. The characteristics of the valve have been analyzed by using a fast ion gauge and a time-of-flight mass-spectrometer. Received: 28 May 2001 / Revised version: 29 June 2001 / Published online: 18 July 2001     

Flashlamp-pumped Ti:Sapphire laser: Influence of the rod figure of merit and Ti3+ concentration

A flashlamp-pumped Ti:Sapphire laser is tested with rods of various Figures of Merit (FOM from 100 to 800) and Ti³⁺ concentrations (0.1 and 0.15% by weight) and we measured the laser energy dependence as a function of these parameters. Output energies above 2 J are obtained without dye converter, leading to a 1.8% overall efficiency and a 2.2% slope efficiency. The effects of pump pulse duration by variation of the discharge capacitance are also monitored.     

Generation of subpicosecond vacuum ultraviolet pulses at 126 nm by using harmonics of a subpicosecond Ti:Sapphire laser

Subpicosecond vacuum ultraviolet (VUV) pulses at the wavelength of 126 nm have been generated in rare gases as a result of the 7th harmonic radiation of a subpicosecond Ti:Sapphire laser oscillating at 882 nm. The VUV harmonic intensity was optimized in Xe at the pressure of 1.2 Torr. The behavior of the harmonic emission was qualitatively reproduced by the classical nonlinear optics. The increase of the harmonic intensity was limited by multiphoton ionization of Xe.     

175 to 210 nm widely tunable deep-ultraviolet light generation based on KBBF crystal

We have developed a widely tunable deep-ultraviolet (DUV) laser in the wavelength range from 175 to 210 nm by the fourth harmonic generation of Ti:Sapphire laser. The fourth harmonic generation is performed by direct second-harmonic generation (SHG) of a frequency doubled Ti:Sapphire laser with KBBF crystal. The highest output power is 2.23 mW at 193 nm, and the power of the DUV laser is more than 1 mW from 182 nm to 210 nm. To our knowledge, it is the first demonstration of milliwatt-level widely tunable DUV all-solid-state laser below 200 nm by direct SHG technique.     

Supercontinuum generation based on nanofiber

Supercontinuum generation (SCG) using a femtosecond Ti:Sapphire laser as a pump source and a nanofiber as a nonlinear element is investigated by numerical modeling. Many parameters are taken into account involving input pulse duration, peak power and diameter of the nanofiber. The results show that the narrower the input pulse is, the easier the SCG could be observed. The relation between the spectrum broadening and the diameter of nanofiber is not a direct proportion. According to our simulation, the dimension of the nanofiber plays an important role in effecting the dispersion and then the generation of supercontinuum.     

50mJ超短脉冲KrF激光系统的参数优化

 介绍了原子能院建立的钛宝石/KrF混合型激光装置，主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构，结合棱镜对进行GVD补偿，获得50mJ，220fs的紫外超短脉冲。用40cm透镜聚焦，靶上功率密度达到10¹⁷ W/cm²。     

Generation of Stable Near－infrared and Violet Femtosecond Pulses from a Self－mode－locked Ti：Sapphire Laser

ＧｅｎｅｒａｔｉｏｎｏｆＳｔａｂｌｅＮｅａｒ－ｉｎｆｒａｒｅｄａｎｄＶｉｏｌｅｔＦｅｍｔｏｓｅｃｏｎｄＰｕｌｓｅｓｆｒｏｍａＳｅｌｆ－ｍｏｄｅ－ｌｏｃｋｅｄＴｉ：ＳａｐｐｈｉｒｅＬａｓｅｒ￥ＬＩＷｅｉｌｉａｎｇ；ＱＩＵＺｈｉｒｅｎ；ＰＥＮＧＷｅｎｊｉ...     

Suppression of gain narrowing in multi-TW lasers with negatively and positively chirped pulse amplification

A laser scheme implementing a combination of negatively and positively chirped pulse amplification (NPCPA) is demonstrated. This method of amplification suppresses spectral narrowing typically appearing in chirped pulse amplification (CPA) lasers thus supporting pulse spectrum much broader than a conventional CPA. With a NPCPA Ti:Sapphire laser we have achieved laser pulses of 50 nm spectral width and 150 mJ energy without any additional spectral correction. The scheme appears as an easy and reliable solution to preserve spectral bandwidth in Ti:Sapphire lasers, especially at high power levels up to the Petawatt regime. PACS 42.60 By, Lh; 42.65 Re     

50mJ超短脉冲KrF激光系统的参数优化

介绍了原子能院建立的钛宝石 /KrF混合型激光装置 ,主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构 ,结合棱镜对进行GVD补偿 ,获得 5 0mJ,2 2 0fs的紫外超短脉冲。用4 0cm透镜聚焦 ,靶上功率密度达到 10 17W/cm2 。     

Half-cycle pulses in the mid-infrared from a two-color laser-induced filament

Four-wave mixing (FWM) of femtosecond near-infrared laser pulses and its second harmonic in the filamentation regime is shown to give rise to ultrashort field waveforms in the mid-infrared with pulse widths as short as a half of the field cycle and produce ultrabroadband supercontinuum spectra stretching from the mid-IR to the terahertz region. Generation of 7-fs pulses centered at 4.35 μm is demonstrated by a two-color filamentation experiment, where the 25-fs, 800-nm fundamental-wavelength output of a Ti: Sapphire laser is mixed with its second harmonic. The spectral and temporal properties of the mid-IR waveforms, as well as their emission pattern, are consistent with the FWM scenario of frequency conversion generalized to include the Kerr effect and ionization-induced refractive-index modulation.     

Two-color facility based on a broadly tunable infrared free-electron laser and a subpicosecond-synchronized 10-fs-Ti:sapphire laser

Subpicosecond synchronization between a mirror-dispersion-controlled 10-fs Ti:sapphire laser and the Free-Electron Laser for Infrared Experiments has been achieved. The measured intensity cross correlation between the two lasers is consistent with a jitter of only 400 fs rms. The wide and continuous tunability of the free-electron laser (FEL; 4.2-300mum) combined with ultrashort pulse duration of six optical cycles and high pulse energy of several tens of microjoules makes a series of two-color experiments possible in a previously inaccessible wavelength range. We demonstrate these capabilities by performing a two-color pump-probe experiment to study carrier cooling in GaAs. A FEL tuned from 8 to 17mum is used as the pump, and a synchronized Ti:sapphire laser pulse serves as the probe.     

氩气中高次谐波辐射的研究

报道了在４５ｆｓ－２ＴＷ激光装置上以Ａｒ惰性气体为介质产生高次谐波的实验结果,实验中通过研究气体密度和激光能量对谐波辐射的影响,找到了适当的气体密度和激光能量范围,并在Ａｒ气中观察到８１次（９．７ｎｍ）的皆波辐射,这时迄今为止,人们在Ａｒ气中所能观测到的最短波长的谐波辐射,经分析表明,高于５７次的谐波是由Ａｒ离子产生的。     

First ultraviolet high-gain harmonic-generation free-electron laser

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.     

Flashlamp-pumped Ti:Sapphire laser with different rods grown by Czochralski and Verneuil methods

The design and the development of a flashlamp-pumped Ti:Sapphire laser is described. Design criteria are discussed and performance improvements using different types of fluorescent UV converters or filters, such as organic dyes or doped glass are presented. We have tested different laser rods at various Ti-concentrations obtained by Verneuil or Czochralski growth techniques. The maximum laser output energy of 540 mJ with a differential efficiency up to 1% was achieved by using only a pyrex filter surrounding the laser rod.Presented at LASERION '91, June 12–14, 1991, München (Germany)     

Tunable Ti: Sapphire regenerative amplifier for femtosecond Chirped-Pulse Amplification

We describe a tunable Ti:Sapphire regenerative amplifier which is used to amplify 120 fs pulses from a self-mode-locked Ti:Sapphire laser to energies in the range of 7–12 mJ from 760 nm to 855 nm. We have used three sets of cavity mirrors in the regenerative amplifier to vary the output wavelength of the laser.On leave from Institute of Laser Engineering, Osaka University, 2-6, Yamada-oka, Osaka 565, Japan (Fax: +81-6/877-4799)     

Phase-matching properties of PPKTP, MgO:PPSLT and MgO:PPcLN for ultrafast optical parametric oscillation in the visible and near-infrared ranges with green pump

Ultrashort pulses with wavelength tuning in the visible and near-infrared (VNIR) ranges (here approximately 680 to 2000 nm) have wide application in many biomedical devices especially in imaging and spectroscopy. The theoretical studies here consider the phase-matching conditions of three periodically poled crystals (PPKTP, MgO:PPcLN and MgO:PPSLT) to use for femtosecond optical parametric oscillators (OPO) to generate wavelength tunability in this range. The basic optical properties and the wavelength tuning ranges are calculated with respect to different grating periods and temperature variation. Dispersive properties of crystals relevant to the ultrafast operation regime are also discussed. The excitation wavelength used here for the analysis is 520 nm which is the second harmonic wavelength of Yb-doped ultrashort pulse solid state lasers. The concept of the tunable femtosecond OPOs with green excitation presented here can be a better alternative to the widely used expensive Ti:Sapphire lasers.     

TW级Ti：Al2O3飞秒激光放大器

报道ＴＷ（１０＾１２Ｗ）级Ｔｉ：Ａｌ２Ｏ３飞秒激光放大器的研究，采用Ｔｉ：Ａｌ２Ｏ３自锁模激光振荡器和脉冲啁啾放大技术，获得了能量为８４ｍＪ，脉宽为７５ｆｓ的放大光脉冲，峰值功率达到ＴＷ量级。     

Intense femtosecond pulse shaping using a fused-silica spatial light modulator

We present the design concept of a setup of a pulse shaper to be used for high-power femtosecond lasers. The pulse shaper is constructed from a high-damage threshold fused-silica spatial light modulator and a 4-f optical system based on the design concept to avoid optical damage. We have successfully demonstrated a pulse compression of 20 fs, 5 mJ pulses obtained from a 1 kHz repetition rate Ti:sapphire chirped pulse amplification system at an average power of 5 W.     

Femtosecond laser micromilling of Si wafers

Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2-8 J/cm² and the milling efficiency attains its maximum between 10 and 20 J/cm².     

Pumping of titanium sapphire laser

Two methods of Ti:Sapphire pumping for the generation of tunable laser radiation in the visible region were studied. For coherent pumping, the radiation of the second harmonic of a Nd:YAP laser was used and a maximum output energy ofE _out=4.5 mJ was reached from the Ti:Sapphire laser. For noncoherent pumping, two different lengths of flashlamp pulses were used and a maximum ofE _out=300 mJ was obtained. Preliminary estimations of the wavelength range of tunability were made.