Passively mode-locked 10 GHz femtosecond Ti:sapphire laser

We report a mode-locked Ti:sapphire femtosecond laser emitting 42 fs pulses at a 10 GHz repetition rate. When operated with a spectrally integrated average power greater than 1 W, the associated femtosecond laser frequency comb contains approximately 500 modes, each with power exceeding 1 mW. Spectral broadening in nonlinear microstructured fiber yields comb elements with individual powers greater than 1 nW over approximately 250 nm of spectral bandwidth. The modes of the emitted comb are resolved and imaged with a simple grating spectrometer and digital camera. Combined with absorption spectroscopy of rubidium vapor, this approach permits identification of the mode index and measurement of the carrier envelope offset frequency of the comb.     

利用SBR实现自启动锁模钛宝石飞秒激光脉冲的产生

利用国内生长的低损耗双量子阱结构的可饱和布拉格反射器在掺钛蓝宝石激光器中实现了可饱和吸收体被动锁模、孤子锁模和KLM锁模状态的自启动稳定运转.当抽运功率为4.5W时，用啁啾镜进行色散补偿，获得了18fs的KLM锁模脉冲，输出功率为150mW. 关键词： 可饱和布拉格反射器 啁啾镜 飞秒 钛宝石激光器     

Sub-two-cycle pulses from a Kerr-lens mode-locked Ti:sapphire laser

Pulses shorter than two optical cycles with bandwidths in excess of 400 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser with a repetition rate of 90 MHz and an average power of 200 mW. Low-dispersion prisms and double-chirped mirrors provide broadband controlled dispersion and high reflectivity. These pulse durations are to our knowledge the shortest ever generated directly from a laser oscillator.     

Direct diode-laser pumping of a mode-locked Ti:sapphire laser

Direct diode-laser pumping of a mode-locked Ti:Al(2)O(3) laser is reported. A single 1 W GaN-based diode laser operating at 452 nm is used as the pump laser. Pulse durations as short as 114 fs and average output powers of up to 13 mW are obtained.     

Cavity-enhanced similariton Yb-fiber laser frequency comb: 3 x 10(14) W/cm2 peak intensity at 136 MHz

We report on a passive cavity-enhanced Yb-fiber laser frequency comb generating 230 MW of peak power (3 kW of average power) at a 136 MHz pulse repetition rate. The intracativy peak intensity of 3 x 10(14) W/cm2 for the 95 fs pulse is sufficient to ionize noble gases, such as Xe, Kr, or Ar. The laser system is based on a mode-locked Yb-fiber similariton oscillator in conjunction with a cladding-pumped chirped-pulse fiber amplifier. After recompression, 75 fs duration pulses at a 13.1 W average power are obtained. These pulses are then coherently added inside a passive ring cavity by controlling the fiber oscillator's pulse repetition rate and carrier-envelope offset frequency. This system is well suited for studying high-field phenomena at very high pulse repetition rates.     

Operation of Kerr-lens mode-locked Ti:sapphire laser in thenon-soliton regime

A Kerr-lens mode-locked Ti:sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti:sapphire laser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37~ps to 2.11~ps, and 36~fs pulses are achieved after extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr?dinger equation, and the simulation results are in good agreement with the experimental results.     

Diode-pumped Kerr-lens mode-locked Ti: sapphire laser with broad wavelength tunability

We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736–825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.     

Hidden instabilities in the Ti:sapphire Kerr lens mode-locked laser

It is experimentally shown that pulse-to-pulse instabilities in the output of Kerr lens mode-locked Ti:sapphire lasers are usual and that they can affect some of the pulse variables (e.g., the spot size) and not others (e.g., pulse duration and energy). These instabilities are not detectable in the averaged signals (such as the autocorrelation of the pulse) that are customarily used for controlling the laser. But, if they are present but are disregarded, these instabilities have undesirable consequences in almost any application. A simple way to detect and eliminate the instabilities is described.     

Three-photon excitation ofp-quaterphenyl with a mode-locked femtosecond Ti:sapphire laser

We observed emission fromp-quaterphenyl (p-QT) at 360 nm when exposed to the focused light from a femtosecond (fs) Ti:sapphire laser at 850 nm. This wavelength is too long to allow two-photon excitation of p-QT. The emission intensity of p-QT was found to depend on the cube of the laser power at 850 nm, suggesting that excitation occurs due to a three-photon process. The same emission spectrum and single exponential decay times were observed for three-photon excitation at 850 nm as for two-photon excitation at 586 nm and for one-photon excitation at 283 nm. The same rotational correlation times were observed for one-, two-, and three-photon excitation, but higher time-zero anisotropies were observed for two- and three-photon excitation. The steady-state anisotropies for one-, two-, and three-photon excitation are precisely consistent with cos², cos⁴, and cos⁶ excitation photoselection, where is the angle between the electric field of the incident light and the absorption dipole. These experiments were performed with 3×10^–5 M solutions of p-QT. Use of such low concentrations was possible because p-QT displays one of the highest apparent cross sections we have observed to date for three-photon excitation. The spatial distribution of the excited fluorescence was less for three-photon excitation than for two-photon excitation of Coumarin 102 at the same 850-nm excitation wavelength. The high cross section, photostability, and clear cos⁶ photoselection of p-QT make it an ideal three-photon standard for spectroscopy and microscopy.     

Generation and characterization of the highest laser intensities (10(22) W/cm2)

We generated a record peak intensity of 0.7 x 10(22) W/cm2 by focusing a 45-TW laser beam with an f/0.6 off-axis paraboloid. The aberrations of the paraboloid and the low-energy reference laser beam were measured and corrected, and a focal spot size of 0.8 microm was achieved. It is shown that the peak intensity can be increased to 1.0 x 10(22) W/cm2 by correction of the wave front of a 45-TW beam relative to the reference beam. The phase and amplitude measurement provides for an efficient full characterization of the focal field.     

Rayleigh-Taylor growth stabilization in direct-drive plastic targets at laser intensities of approximately 1 x 10(15) W/cm2

Direct-drive, planar-target Rayleigh-Taylor growth experiments were performed for the first time to test fundamental physics in hydrocodes at peak drive intensities of ignition designs. The unstable modulation growth at a drive intensity of approximately 1 x 10(15) W/cm2 was strongly stabilized compared to the growth at an intensity of approximately 5 x 10(14) W/cm2. The experiments demonstrate that standard simulations based on a local model of electron thermal transport break down at peak intensities of ignition designs (although they work well at lower intensities). The preheating effects by nonlocal electron transport and hot electrons were identified as some of the stabilizing mechanisms.     

Ultralow-threshold Kerr-lens mode-locked Ti:Al(2)O(3) laser

An ultralow-threshold Kerr-lens mode-locked Ti:Al(2)O(3) laser achieved by use of an extended cavity design is demonstrated. Mode-locking thresholds as low as 156 mW are achieved. Pulses with durations as short as 14 fs and bandwidths of >100 nm with output powers of ~15 mW at 50-MHz repetition rates are generated by only 200 mW of pump power. Reducing the pump power requirements to a factor of 10x less than required by most conventional Kerr-lens mode-locked lasers permits inexpensive, low-power pump lasers to be used. This will facilitate the development of low-cost, high-performance femtosecond Ti:Al(2)O(3) laser technology.     

Self-starting mode-locked picosecond Ti：sapphire laser by using of a fast SESAM

A stable continuous wave mode-locked picosecond Ti:sapphire laser by using a fast semiconductor saturable absorber mirror (SESAM) is demonstrated. The laser delivers pulse width of 20 ps at a central wavelength of 813 nm and a repetition rate of 100 MHz. The maximum output power is 1.34 W with pump power of 7 W which corresponds to an optical--optical conversion efficiency of 19.1%.     

10 kHz 40 W Ti:sapphire regenerative ring amplifier

A cryogenically cooled Ti:sapphire regenerative ring amplifier was developed as a laser for generating a laser-produced plasma light source. With a 10 kHz 180 W pump laser, the amplifier output is 40 W before compression and 26 W after compression. We believe it to be the current highest average-power output from a single stage Ti:sapphire amplifier. The effective focal length of the thermal lens is measured to be 2.2 m at 100 K for 180 W of pump power. With a 1 m focal length lens placed in the resonator, the effect of a thermal lens on the resonator mode is suppressed. High conversion efficiency is achieved for the whole pumping power range without any additional measures for thermal compensation.     

Application of a femtosecond self-sustaining mode-locked Ti:sapphire laser to the field of laser scanning confocal microscopy

Developments in ultrafast Ti:sapphire laser technology can be applied in the investigation of nonlinear optical processes. We describe the application of a self-sustaining femtosecond Ti:sapphire laser as an illumination source in the field of confocal laser scanning fluorescence microscopy (LSM). We present spectra for various fluorescent stains under two-photon excitation and present LSM images of stained samples under mode-locked illumination. The potential for such a system as a non-destructive technique for studying live cells in biomedical research is discussed.     

A laser system producing 5×1019 W/cm2 at 10 Hz

19 W/cm² have been achieved. Received: 10 March 1997/Revised version: 26 April 1997     

自启动KLM钛宝石激光器谐振腔的理论计算

运用四阶RungeKutta法直接求解非线性介质内椭圆高斯光束传播方程组的方法分析增益介质内的克尔透镜(Kerrlens)效应,结合在增益介质外运用的线性ABCD矩阵寻找自洽解,对半导体可饱和吸收镜(SESAM)启动的高功率KLM钛宝石激光器谐振腔的像散、稳定性、光束参数、自聚焦效应和克尔自聚焦强度与腔参数的关系进行了系统的理论计算.计算结果与实验结果相符合.该计算为SESAM启动的五镜腔KLM激光器的设计和调整提供了理论依据 关键词： 克尔透镜锁模 飞秒 半导体可饱和吸收镜 五镜腔     

Sub-10-fs, terawatt-scale Ti:sapphire laser system

A three-stage, 1-kHz amplifier system delivering pulses shorter than 10 fs with a peak power in excess of 0.3 TW is reported. Passive and active spectral intensity and phase control allows the preservation of a bandwidth of 120 nm (FWHM) to as high as multimillijoule energy levels and temporal compression of the broadband pulses close to their Fourier limit. The system is scalable to peak powers well beyond 1 TW and holds promise for substantially advancing the state of the art of coherent laboratory soft-x-ray sources.