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1.
Mechanisms of femtosecond laser nanosurgery of cells and tissues 总被引:6,自引:0,他引:6
We review recent advances in laser cell surgery, and investigate the working mechanisms of femtosecond laser nanoprocessing
in biomaterials with oscillator pulses of 80-MHz repetition rate and with amplified pulses of 1-kHz repetition rate. Plasma
formation in water, the evolution of the temperature distribution, thermoelastic stress generation, and stress-induced bubble
formation are numerically simulated for NA=1.3, and the outcome is compared to experimental results. Mechanisms and the spatial
resolution of femtosecond laser surgery are then compared to the features of continuous-wave (cw) microbeams. We find that
free electrons are produced in a fairly large irradiance range below the optical breakdown threshold, with a deterministic
relationship between free-electron density and irradiance. This provides a large ‘tuning range’ for the creation of spatially
extremely confined chemical, thermal, and mechanical effects via free-electron generation. Dissection at 80-MHz repetition
rate is performed in the low-density plasma regime at pulse energies well below the optical breakdown threshold and only slightly
higher than used for nonlinear imaging. It is mediated by free-electron-induced chemical decomposition (bond breaking) in
conjunction with multiphoton-induced chemistry, and hardly related to heating or thermoelastic stresses. When the energy is
raised, accumulative heating occurs and long-lasting bubbles are produced by tissue dissociation into volatile fragments,
which is usually unwanted. By contrast, dissection at 1-kHz repetition rate is performed using more than 10-fold larger pulse
energies and relies on thermoelastically induced formation of minute transient cavities with lifetimes <100 ns. Both modes
of femtosecond laser nanoprocessing can achieve a 2–3 fold better precision than cell surgery using cw irradiation, and enable
manipulation at arbitrary locations.
PACS 42.62.Be; 72.20.Jv 相似文献
2.
Optical breakdown and filamentation of femtosecond laser pulses propagating in air at a kHz repetition rate 总被引:1,自引:0,他引:1 下载免费PDF全文
We report the experiments on the optical breakdown and filamentation of femtosecond laser pulses propagating in air at a kHz repetition rate and with several hundreds micro-joule-energy.A 10m-long filament and its breakup and merging at the nonlinear focal region produced by modulational instability of femtosecond laser pulses in air are observed.A simple model based on the nonlinear Schroedinger equation coupled with multiphoton ionization law is presented to explain the several experimental results. 相似文献
3.
We demonstrate a high-energy near-infrared cavity-dumped femtosecond optical parametric oscillator (OPO) based on periodically poled lithium niobate. The laser generates 90 nJ pulses at a repetition rate of up to 1 MHz when synchronously pumped by 800 mW output from a femtosecond Ti:sapphire laser. The laser is broadly tunable from 1.0 to 1.5 microm in the signal branch, with a pulse duration of < 60 fs at 1.2 microm. High intracavity power is achieved by running the laser in the regime of positive group-velocity dispersion. 相似文献
4.
Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy 总被引:13,自引:0,他引:13
Using tightly focused femtosecond laser pulses of just 5 nJ, we produce optical breakdown and structural change in bulk transparent materials and demonstrate micromachining of transparent materials by use of unamplified lasers. We present measurements of the threshold for structural change in Corning 0211 glass as well as a study of the morphology of the structures produced by single and multiple laser pulses. At a high repetition rate, multiple pulses produce a structural change dominated by cumulative heating of the material by successive laser pulses. Using this cumulative heating effect, we write single-mode optical waveguides inside bulk glass, using only a laser oscillator. 相似文献
5.
Cho SH Kärtner FX Morgner U Ippen EP Fujimoto JG Cunningham JE Knox WH 《Optics letters》2001,26(8):560-562
We demonstrate the generation of high-energy pulses by using a low-repetition-rate Kerr-lens mode-locked laser. Repetition rates as low as 4 MHz were achieved with a long, multiple-pass cavity and a semiconductor saturable Bragg reflector. The laser generated pulses of 55-fs duration with a pulse energy of 48 nJ when it was mode locked in the net negative dispersion regime. Mode locking in the positive dispersion regime reduces instabilities and enables pulses to have durations of 80 fs and energies as high as 90 nJ. This is, to our knowledge, the highest pulse energy and the lowest repetition rate ever generated directly from a femtosecond laser resonator without cavity dumping. 相似文献
6.
N.T. Nguyen A. Saliminia S.L. Chin R. Vallée 《Applied physics. B, Lasers and optics》2006,85(1):145-148
Writing conditions for the fabrication of optical waveguides in bulk fused silica glass by use of 1 kHz focused femtosecond laser pulses at 800 nm were systematically determined for different focusing geometries. The results demonstrate that waveguides can be formed based on optical breakdown, filamentation (single or multiple), or a combination of both processes, when using pulse energies lower than the threshold of structural damage. The mechanisms of laser-induced index change are also discussed. PACS 42.65.Jx; 42.70.Ce; 42.79.Gn 相似文献
7.
Multiplying the repetition rate of passive mode-locked femtosecond lasers by an intracavity flat surface with low reflectivity 总被引:1,自引:0,他引:1
By inserting a low-reflectivity flat surface inside the oscillator cavity, we demonstrate a flexible and phase-insensitive method for multiplying the repetition rate of a femtosecond passive mode-locked solid-state laser. Without mode matching and feedback control, we successfully multiplied the repetition rate of a passively mode-locked Cr:forsterite laser from 124 MHz to 1.24 GHz. High-repetition-rate femtosecond optical pulses with average power of >100 mW can be obtained with the demonstrated method. 相似文献
8.
A.P. Joglekar H. Liu G.J. Spooner E. Meyhöfer G. Mourou A.J. Hunt 《Applied physics. B, Lasers and optics》2003,77(1):25-30
A remarkable feature of material damage induced by short-pulsed lasers is that the energy threshold becomes deterministic for sub-picosecond pulses. This effect, coupled with the advent of kHz and higher repetition rate chirped pulse amplification systems, has opened the field of femtosecond machining. Yet the mechanism of optical breakdown remains unclear. By examining the damage threshold as a function of polarization, we find that, contrary to established belief, multiphoton ionization plays an insignificant role in optical breakdown. The polarization independence, combined with the observed precise and uniform dielectric breakdown threshold even for nanometer-scale features, leads us to conclude that the fundamental mechanism is self-terminated Zener-impact ionization, and that the deterministic and uniform damage threshold throughout the sample threshold stems from the uniform valence-electron density found in good-quality optical materials. By systematically exploring optical breakdown near threshold, we find that we can consistently machine features as small as 20 nm, demonstrating great promise for applications ranging from Micro ElectroMechanical Systems (MEMS) construction and microelectronics, to targeted disruption of cellular structures and genetic material. PACS 32.80.Rm; 77.22.Jp; 81.16.-c 相似文献
9.
10.
E. Roissé V. Couderc A. Barthélémy F. Louradour 《Applied physics. B, Lasers and optics》1999,69(2):89-91
We report the first diode-pumped solid-state laser operating in cw-mode-locked regime and simultaneously achieving intracavity
frequency-tripling. This laser provide UV picosecond pulses (λ=355 nm) of 10 ps duration with 0.5 mW average power at 150 MHz
repetition rate. A different set of adjustments gave rise to a Q-switched mode-locked regime. Trains of hundred UV pulses
of 60 ps duration and 4 W peak power were produced in this latter case at 50 kHz repetition rate.
Received: 12 October 1998 / Revised version: 12 December 1998 / Published online: 26 May 1999 相似文献
11.
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. 相似文献
12.
We demonstrate high-speed terahertz (THz) time-domain spectroscopy based on electronically controlled optical sampling (ECOPS). The ECOPS system utilizes two synchronized Ti:sapphire femtosecond lasers with a 100 MHz repetition frequency. The time delay between the two laser pulses is demonstrated to be rapidly swept at a scan rate of 1 kHz on a time delay window of 77 ps by using an external offset voltage applied to a locking electronics. It is shown that a THz pulse can be exactly measured by ECOPS, as is done by asynchronous optical sampling (ASOPS), and the measurement time is shortened by a factor of 50 by using ECOPS compared with ASOPS in the case of employing 100 MHz repetition-rate lasers. 相似文献
13.
14.
Fiber-laser-based femtosecond parametric generator in bulk periodically poled LiNbO(3) 总被引:1,自引:0,他引:1
A diode-pumped system for optical parametric generation of wavelength-tunable femtosecond pulses is demonstrated. It comprises an Er-doped fiber mode-locked laser, a fiber chirped-pulse amplifier, and a bulk periodically poled LiNbO(3) (PPLN) optical parametric generator. The parametric generator is pumped at 777 nm with frequency-doubled microjoule pulses from the fiber amplifier and produces 300-fs pulses tunable from 1 to 3microm with output energies up to ~200 nJ. Use of a PPLN nonlinear crystal substantially reduces the pump energies required for efficient parametric generation. Saturated single-pass parametric energy conversion of 38% (internal) has been achieved with only 220 nJ of pump inside the crystal. A parametric generation threshold of 54 nJ is observed, and efficient parametric conversion is obtained with repetition rates up to 200 kHz. 相似文献
15.
针对高能量千赫兹重复频率飞秒激光的应用需求,设计了一套采用线性再生腔结构的高效率飞秒钛宝石激光啁啾脉冲放大系统.通过优化腔型设计,在重复频率为1 kHz、单脉冲能量为20 mJ的527 nm激光抽运下,将展宽后的800 nm啁啾脉冲激光的能量放大到5.8 mJ,对应斜效率达到30.7%.进一步通过色散补偿压缩脉冲宽度,获得了单脉冲能量为4 mJ、脉冲宽度为45.7 fs的输出,稳定性测量表明激光的能量抖动仅为0.18%(均方根值). 相似文献
16.
为了探索大模场面积光子晶体光纤锁模激光器在全正色散锁模域内的耗散孤子锁模机理, 以获得更大的单脉冲能量和更高的峰值功率, 本文搭建了以掺镱大模场面积光子晶体光纤作为增益介质的耗散孤子锁模激光器. 激光器使用环形腔结构, 利用非线性偏振旋转以及滤光片提供的耗散作用实现了稳定的锁模运转. 实验中, 从激光器振荡级直接获得了平均功率10 W, 重复频率49.09 MHz(对应202 nJ的单脉冲能量), 脉冲宽度为1.03 ps的稳定锁模脉冲输出, 经过腔外色散补偿得到的脉冲宽度为95.5 fs. 相似文献
17.
Single-shot laser damage threshold of MgO for 40-986 fs, 800 nm laser pulses is reported. The pump-probe measurements with femtosecond pulses were carried out to investigate the time-resolved electronic excitation processes. A theoretical model including conduction band electrons (CBE) production and laser energy deposition was applied to discuss the roles of multiphoton ionization (MPI) and avalanche ionization in femtosecond laser-induced dielectric breakdown. The results indicate that avalanche ionization plays the dominant role in the femtosecond laser-induced breakdown in MgO near the damage threshold. 相似文献
18.
We present results on the surface-damage threshold of lithium niobate after single-and multiple-femtosecond laser pulse irradiation at the pulse duration of 80 fs, with a 800-nm wavelength, and a repetition rate of 1 kHz. The surface-ablation threshold was found to decrease significantly with an increase in the pulse number applied to the surface until reaching an almost constant level due to an incubation effect, which is attributed to the laser-induced defect formation. The threshold of lithium niobate under a single shot is found to be 2.82 J/cm2, and the threshold fluence for an infinite number of pulses F th(∞) converges to a common value of 0.52 ± 0.06 J/cm2 for N > 80. The results have the potential for application in laser micromachining and the fabrication of related optical devices and applications in frequency conversion by a femtosecond laser in lithium niobate. 相似文献
19.
Jinghua Han Qiuhui Zhang Weixing Fan Liming Yang Qihua Zhu 《Applied Surface Science》2010,256(22):6649-6654
The characteristics and mechanisms of the damage to absorbing glass with high-repetition laser pulses (several kHz) are discussed. The results show that: (1) in the range of comparatively low-repetition rate, the damage is characterized by material melting and a small crater on the surface of substrate; (2) with the increase in repetition rate, a bigger and deeper crater is surrounded by re-deposition and crystalline granules originating from the cooling of vapor; and (3) the crater, surrounded by evaporation and an large number of solid particulates which is obviously the characters of phase explosion, becomes even bigger and deeper when the repetition rate is further increased. We modeled the temperature distribution in different repetition rate regime and found that heat accumulation plays a significant role in damage process. Because of the temperature dependence of damage mechanism, the temperature of the area irradiated by laser beam will ramp up with increasing the repetition rate, which triggers the melting and evaporation of dielectrics and phase explosion successively. Our results may benefit the understanding of laser-induced damage in optical materials. 相似文献
20.
Turkka Salminen Mikko Hahtala Ilkka Sepp?l? Pekka Laukkanen Tapio Niemi 《Applied Physics A: Materials Science & Processing》2010,101(4):735-738
Thin films of yttria stabilized zirconia were deposited onto silicon substrates using high repetition rate picosecond pulse
lasers. The applied lasers covered the repetition rate range from 10 kHz to 4 MHz. We found that the laser pulse overlapping
which results from increased repetition rates led to considerable changes in the ablation process. Defect formation and local
heating lead to lower ablation thresholds and, with sufficiently high repetition rates, to melting of the target and even
to thermal evaporation. We found that yttria-stabilized zirconia (YSZ) films deposited with picosecond pulses at 1064 nm wavelength
below repetition rates of 2 MHz have rough, nanostructured morphology and the same atomic ratio of yttrium and zirconium as
the target. Films deposited with 2 MHz and higher repetition rates with high number of overlapping pulses are very smooth,
but are yttrium deficient, providing evidence of the importance of the thermal processes. 相似文献