PurposeThis work demonstrates significant advantages in ophthalmic surgeries through the use of picosecond ultrashort laser pulses instead of state-of-the-art nanosecond laser pulses. These ultrashort lasers shall serve as universal tools more effectively combining advantages of high precision, low impact and economic advantages compared to existing instruments.MethodsAs samples, we used post-mortem porcine eyes on which we performed the experiments with both picosecond and nanosecond lasers. Performed surgeries were laser iridotomy, (post-) cataract treatment/capsulotomy and selective laser-trabeculoplasty. Pulse widths were between 12 ps and 220 ns with pulse energies between 30 μJ and 10 mJ at 532 nm and 1,064 nm. Additionally, we investigated accompanying shock waves, cavitation bubbles, and heat effects during the ablation processes.ResultsFor all surgeries, significant differences were observed between picosecond and nanosecond pulses: It was possible to scale the pulse energy down to 10 of microjoules rather than requiring millijoules, and resulting tissue ablations are much more precise, more deterministic and less frayed. The shock wave and cavitation bubble investigation revealed major differences in pressure between picosecond pulses (0.25 MPa, 50 μJ) and nanosecond pulses (37 MPa, 5 mJ). The heat input during ablation could be lowered by two orders of magnitude.ConclusionPicosecond ultrashort laser pulses show substantial benefits for several ophthalmic surgeries, with regard to ablation precision, shock wave generation and heat input. They are better than state-of-the-art ophthalmic nanosecond lasers in all aspects tested.

We demonstrate sub-100 ps pulses with a Yb3+:YAG microchip laser passively Q-switched by a Cr4+:YAG saturable absorber. By introducing a subcavity, the laser threshold and the saturation energy are decreased which helps to prevent damage and to vary the effective emission and absorption cross sections. Pulse widths of 84 ps, repetition rates of 3.3 kHz and pulse energies of 32 μJ are achieved. This allows direct micromaterial processing e.g. for ophthalmic surgeries. To the best of our knowledge, this is the first sub-100 ps Yb3+:YAG/Cr4+:YAG microchip laser. A new approximation is used to calculate the rate equations for multiple longitudinal modes and to determine the threshold for single-longitudinal-mode operation.

The laser systems currently used in ophthalmology either have some pulse length dependent side effects or are very expensive due to their complexity. Therefore, a newly developed approach using picosecond laser sources is investigated. These lasers combine the advantages of the low price of currently used short-pulse laser sources with the cold material ablation possibilities of high-end femtosecond sources. The surgeries intended are laser iridotomy, capsulotomy/post-cataract treatment and selective laser-trabeculoplasty (SLT). They are demonstrated on post mortem porcine eyes. The result is a more precise, less frayed tissue ablation with picosecond pulses in comparison to nanosecond pulses. The pulse energy could be reduced to (50 20) µJ per pulse instead of 1mJ to 10mJ per pulse, which is currently applied. The study of shock waves and cavitation bubbles revealed a huge difference in pressure between picosecond pulses (0:25MPa at 50 µJ) and nanosecond pulses (37MPa at 5 mJ). Therefore, the risk of collateral damage leading to potential additional clinical patterns and adverse effects could be significantly reduced.

We report on a passively mode-locked, diode-pumped femtosecond laser that provides similar to 200fs, 1053nm optical solitonlike pulses with < 8 orders of magnitude (OM) temporal contrast. The average output power of the compact, air-cooled laser is similar to 450mW at 77MHz pulse repetition rate. The spectral bandwidth (FWHM) is around 5-6nm, corresponding to transform limited pulses. For synchronization purposes the pulse repetition rate can be fine tuned to and continuously kept at a desired value employing a controller circuit, a motorized translation stage and a piezo actuator. The center wavelength of the pulses is tunable and can be precisely set to 1053nm by adjusting the laser pump power. The selfstarting laser is mode-locked using a semiconductor saturable absorber mirror (SESAM). The SESAM parameters are optimized for producing fs pulses with high temporal contrast. The effects of an intra-cavity fused silica plate inserted near Brewster angle and used for fine wavelength tuning and for polarization selection on the temporal contrast of the emitted pulses are discussed. The high temporal contrast pulses from this laser oscillator are well suited for seeding very high gain, multiple Joule type, Nd:glass, chirped pulse amplification systems routinely used in high intensity laser interaction experiments. The automated high dynamic range autocorrelator (HDR-AC) capable of recording the autocorrelation trace over 8 OM is described. The HDR-AC is based on a BBO crystal for second harmonic generation and a PMT for high sensitivity detection. A lock-in amplifier increases the detectable signal range by similar to 2 OM.

We present a passively Q-switched Nd3+:YAG/Cr4+:YAG laser with subsequent nonlinear pulse compression. This miniature laser combines both the high pulse energy of several tens of micro Joules and the short pulse duration of <20 ps without any amplification. It is therefore readily usable for many ultrafast applications including micro machining and medical applications. With these parameters, the laser shows a new level of compactness in comparison to other sub-100 picosecond laser sources. We utilize a Nd3+:YAG and a Cr4+:YAG crystal in a flat-Brewster, Brewster-flat configuration, respectively, positioned closely and the Brewster faces adjacent to each other. Pumped with approx. 6W from a fiber-coupled, 808 nm laser diode, the miniature, passively Q-switched laser oscillator delivers a pulse energy of 54 ILEJ with a pulse width of 339 ps and a repetition rate of 8.5 kHz. These pulses are subsequently coupled into a 20 lam core dia. large mode area PM fiber. Following a fiber propagation of 1.65 m the pulses are spectrally broadened by about a factor 40 due to self-phase modulation. Thereafter the nearly linearly chirped laser pulses are compressed by a chirped volume Bragg grating (CVBG). The optimized laser output pulses have a pulse width of 11.8 ps and a pulse energy of 20 mu J. We measured the polarized (PER>20dB) beam quality to be close to the diffraction limit with an M-2 approximate to 1.5. A 13 hours continuous, stable laser operation has indicated a good long term stability and reliability.

The application of these lasers outside research laboratory environments has been, up to now, very limited because of their complexity and difficulty of operation, and because of the high prices of commercially available laser systems. In terms of both pulse energy and repetition rate, cavity-dumped laser systems are in between oscillators and amplifier systems, and thus are ideal laser sources for many applications such as microstructuring, laser surgery, tissue manipulation, multiphoton microscopy, and laser spectroscopy. The first part of this chapter is organized as follows: After a brief description of the laser setup, we introduce three dynamic regimes which are dependent on different dumping frequencies. The pulse-to-pulse stability, the transient spectra, and autocorrelations are discussed with respect to the theoretical model. A numerical evaluation of the laser dynamics is carried out and compared to the experimental results.

Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 to 2 MHz, and micro Joule level pulse energies. Most systems are based on short pulse modelocked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50 μm long Nd:YVO4-gain material optically bonded to a 4.6 mm thick undoped YVO4-crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 – 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nJ. These 40-ps pulses are spectrally broadened in a standard single mode fibre and then compressed in a 24 mm long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from app. 0.2 to 1.4 MHz by changing the pump power while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fibre is observed throughout the pulse repetition rate, supporting sub-10- ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4-amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

Short-pulse laser systems have found entry into industrial micro material fabrication processes on a large scale during the past ten years. In the same way the demand of simple, compact and cost-efficient seed sources has grown. The physical parameters needed for short-pulse laser processing range between a few femtoseconds to some ten picoseconds at repetition rates of up to 1 MHz. Up to now these laser systems are based on high repetition rate oscillators and regenerative amplifiers. These systems are rather complex and expensive. In contrast a Q-switched microchip laser in combination with a single pass amplifier permits a much simpler approach. In the following we present a 50 μm Nd3+:YVO4 microchip laser that is passively Q-switched by a semiconductor saturable absorber mirror. To overcome handling problems of the small crystal dimensions the 50 μm 3 at.-% doped Nd3+:YVO4 crystal is optically bonded to an undoped YVO4 crystal of a length of about 500 μm. The system provides pulse widths around 26 ps at a repetition rate of up to 0.9 MHz. The average output power is 15 mW at a wavelength of 1,064 nm, at an energy of 17 nJ. We will discuss the prospects and limits in terms of pulse width, repetition rate, output power, and system stability. The experimental data are compared to theoretical calculations.

We present a 50 μm Nd3+:YVO4 microchip laser that is passively Q-switched by a semiconductor saturable absorber mirror. To reduce handling problems caused by the small crystal dimensions, the 50 μm Nd3+:YVO4 crystal is optically bonded to an undoped YVO4 crystal of a length of about 500 μm. By using a saturable absorber mirror with an effective modulation depth of >10% the system is able to deliver 16 ps pulses at a repetition rate of up to 1.0 MHz. The average laser power is 16 mW at 1064 nm. To our knowledge these are the shortest Q-switched pulses ever reported from a solid-state laser. The limits in terms of pulse width, repetition rate, output power, and system stability are discussed. Additionally, continuous-wave behavior is analyzed. Experimental data is compared with the simulation results of the coupled rate equations.

High average power, high repetition rate ultrashort pulse (pulse duration < 10 ps) laser systems with µJ pulse energies [1, 2] are increasingly used for bio-medical and material processing applications. Interesting applications for the ultrashort pulse laser systems are in the field of selective structuring of thin-films. Thin-film solar cells have shown a big potential to decrease cost of manufacturing for photovoltaic generation. Despite many research attempts to optimize materials the mass production of thin-film solar cells is still looking for versatile tools for the structuring of the thin-film coated area, where thin films with a thickness of ca. 1 µm have to be line structured with galvanic separation without damaging the substrate or any other layers.In this paper we report on recent results on the selective ablation of transparent conductive oxide (TCO) thin film, i.e. Boron-doped ZnO. The multi-pulse process thresholds were determined for direct and induced (lift off) laser-processing. From comparison of the process thresholds for both methods we can conclude that the induced ablation is more suitable for the structuring of the TCO layer. On the other hand, structuring of the TCO layers by induced ablation is more complicated due to its strong dependence on the quality of the glass substrate.

We quantitatively predict the observed continuum-like spectral broadening in a 90-mm weakly birefringent all-normal dispersion-flattened photonic crystal fiber pumped by 1041-nm 229-fs 76-MHz pulses from a solid-state Yb:KYW laser. The well-characterized continuum pulses span a bandwidth of up to 300 nm around the laser wavelength, allowing high spectral power density pulse shaping useful for various coherent control applications. We also identify the nonlinear polarization effect that limits the bandwidth of these continuum pulses, and therefore report the path toward a series of attractive alternative broadband coherent optical sources.

Dispersion-managed mode-locked (DM-KLM) (Ti:sapphire) lasers [1] are the work horses in the domain of sub-10 fs laser pulses. Since the first observation of Kerr-lens mode-locking (KLM) in 1991 [2], continuous laser development has lead to the generation of octave-spanning spectra and 5-fs pulses directly from the oscillator [3],[4]. DM-KLM lasers exploit the intensity dependent nonlinear refractive index in conjunction with a careful management of the distribution of discrete dispersive elements inside the cavity. In the time domain, this leads to self-phase modulation and hence additional spectral broadening, whereas in the transverse spatial beam dimensions, the buildup of a Kerr-lens together with a suitable resonator geometry enables efficient gain modulation to favor pulsed operation in comparison to the continuous wave (CW) operation. However, KLM lasers with pulse durations below a few tens of femtoseconds are generally not, and usually require, external (mechanical) perturbations to initiate mode-locking.

We report smooth and broad continuum generation using a compact femtosecond Ti:Sapphire laser as a pump source and a tapered photonic crystal fibre as a nonlinear element. Spectral output is optimized for use in optical coherence tomography, providing a maximum longitudinal resolution of 1.5 microm in free space at 809 nm centre wavelength without use of additional spectral filtering.

Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text H. Huber, S. Zoppel, M. Lederer, J. Smolenski, R. Braunschweig, and D. Kopf, "High Repetition Rate Micromachining of Dielectrics and Ceramics with Ultrafast Lasers," in Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optica Publishing Group, 2006), paper PWE1. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Ultrahigh resolution optical coherence tomography (OCT) is demonstrated at 800 nm and 1300 nm using continuum generation in a single photonic crystal fiber with a parabolic dispersion profile and two closely spaced zero dispersion wavelengths. Both wavelengths are generated simultaneously by pumping the fiber with ~78 mW average power at 1064 nm in a 52 MHz, 85 fs pulse train from a compact Nd:Glass oscillator. Continuum processes result in a double peak spectrum with > 110 nm and 30 mW average power at 800 nm and > 150 nm and 48 mW at 1300 nm. OCT imaging with < 5 mum resolution in tissue at 1300 nm and < 3 mum resolution at 800 nm is demonstrated. Numerical modeling of propagation was used to predict the spectrum and can be used for further optimization to generate smooth, broad spectra for OCT applications.