Laser-induced damage mechanisms were investigated for an ultra-broadband chirped mirror, as part of a systematic
study of few-cycle pulse laser-induced damage threshold (LIDT) of widely-used ultra-broadband optics,
in vacuum and in air, for single and multi-pulse regimes (S-on-1). Microscopic analysis of damage morphology
suggests that three different damage mechanisms occur across the fluence range 0.15-0.4J/cm2, while no ablation
was yet observed. The three regimes resulted in shallow swelling (< 10 nm tall), tall blistering (~ 150 nm
tall), and annular blistering (damage suppressed at highest intensity, forming a ring shape). Descriptions of the
potential mechanisms are discussed.
The feed-forward technique has recently revolutionized carrier-envelope phase stabilization, enabling unprecedented
values of residual phase jitter. Nevertheless, in its original demonstrations the stabilized beam exhibited angular and
temporal dispersion. We demonstrate that these problems can be solved, resulting in few-cycle pulses with good beam
quality. This in turn enables the use of monolithic interferometers, providing excellent long-term stability of the system.
Out-of-loop RMS phase noise of less than 80 mrad over 33 minutes (0.5 mHz to 5 kHz) is measured, i.e., a value that has
previously been reported for a few seconds integration time. The current method promises to enable reliable operation of
CEP-stable systems over several days.
Ultrashort pulse fiber delivery for Ti:Sapphire lasers is basically restricted to distances below a few meters which is due
to the application of dispersion compensating devices that are not capable of managing third and higher order material
dispersion. By the use of a fiber delivery concept based on higher order mode fibers ultrashort laser pulses in the 800 nm
wavelength range are transmitted over 20 meters without the need for pulse pre-chirping. For the first time a large
distance fiber delivery module is demonstrated, revealing its potential for remote THz imaging or spectroscopy using
ultrashort laser pulses. Application of the fiber delivery is demonstrated by generating and detecting broadband THz
radiation at the fiber output.
220-nJ, 42-fs, 5.25-MHz pulses from a long-cavity Ti:Sapphire chirped pulse oscillator were spectrally broadened by
nonlinear propagation in a Sapphire plate. The chirp was subsequently compensated with dispersive mirrors. After farfield
spatial filtering the compressor delivered 80-nJ, sub-15-fs pulses at 5.25 MHz.
A novel 500-nJ Oscillator has been developed in order to investigate the energy-scaling potential of this compression
scheme. 16-fs 130-nJ compressed pulses were obtained with this source. A second compression stage has been
calculated and designed in order to reduce the pulse duration down to < 10 fs.
Although fiber delivery of 25 fs laser pulses were recently shown possible reported results are restricted to 1 to 2 m
single-mode optical fiber due to the high amount of group delay dispersion, guiding losses or fiber nonlinearities. On the
other hand conceivable applications of ultrashort laser pulses in inhospitable environment, their use for security or even
telecommunication purposes require optical pulses to be delivered over much longer fiber distances. Here we
demonstrate 160 fs laser pulses from a Ti:Sapphire laser travelling over 45 m optical fiber. In theory even 130 fs can be
sent through 50 m single-mode fiber with the herein described technique.
Circularly polarized, 25 fs 5 mJ pulses generated at a repetition rate of 1 kHz from a two-stage chirped pulse amplifier
were spectrally broadened by means of nonlinear propagation in a Ne-filled hollow fiber. Subsequent compression with
dispersive mirrors resulted in 5.2 fs, 1.7 mJ pulses. After recompression an all-reflective achromatic phase retarder was
used to obtain linear polarization.
It has long been considered that the advantages emerging from employing chirp pre-compensation in nonlinear
microscopy were overweighed by the complexity of prism- or grating-based compressors. These concerns were refuted
with the advent of dispersive-mirrors-based compressors that are compact, user-friendly and sufficiently accurate to
support sub-20-fs pulse delivery. Recent advances in the design of dispersive multilayer mirrors resulted in improved
bandwidth (covering now as much as half of the gain bandwidth of Ti:Sapphire) and increased dispersion per bounce
(one reflection off a state-of-the-art dispersive mirror pre-compensates the dispersion corresponding to >10mm of glass).
The compressor built with these mirrors is sufficiently compact to be integrated in the housing of a sub-12-fs Ti:Sapphire
oscillator. A complete scanning nonlinear microscope (FemtOgene, JenLab GmbH) equipped with highly-dispersive,
large-NA objectives (Zeiss EC Plan-Neofluoar 40x/1.3, Plan-Neofluar 63x/1,25 Oil) was directly seeded with this negatively chirped laser. The pulse duration was measured at the focus of the objectives by inserting a scanning autocorrelator in the beam path between the laser and the microscope and recording the second order interferometric autocorrelation traces with the detector integrated in the microscope. Pulse durations <20fs were measured with both objectives. The system has been applied for two-photon imaging, transfection and optical manipulation of stem cells. Here we report on the successful transfection of human stem cells by transient optoporation of the cell membrane with a low mean power of < 7 mW and a short μs beam dwell time. Optically transfected cells were able to reproduce. The daughter cell expressed also green fluorescent proteins (GFP) indicating the successful modification of the cellular DNA.
We demonstrated that the dispersion of scanning microscope optics (including a Zeiss 40x/1.2 Apochromat objective)
can be compensated by means of chirped mirrors over a bandwidth of 170 nm at 800 nm. The interferometric
autocorrelation trace recorded at the focus of the microscope objective with a two-photon diode indicated a pulse
duration of < 12 fs. The propagation time difference of the system can be minimized by proper choice of the
components, enabling sub-12-fs pulse delivery with a completely filled 40x/0.8 Zeiss Achroplan water immersion
We have developed a multiphoton microscopy (MPM) system using a 12-fs Ti:sapphire laser with adjustable dispersion precompensation in order to examine the impact of pulse duration on nonlinear optical signals. The efficiencies of two-photon-excited fluorescence (TPEF) and second harmonic generation (SHG) were studied for various pulse durations, measured at the sample, ranging from ~400 fs to sub-20 fs. Both TPEF and SHG increased proportionally to the inverse of the pulse duration for the entire tested range. Because of improved signal-to-noise ratio, sub-20-fs pulses were used to enhance MPM imaging depth by approximately 160%, compared to 120-fs pulses, in human skin.
Multiphoton microscopy (MPM) has become an important tool for high-resolution and non-invasive imaging in biological tissues. However, the efficiencies of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) are relatively low because of their nonlinear nature. Therefore, it is critical to optimize laser parameters for most efficient excitation of MPM. Reducing the pulse duration can increase the peak intensity of excitation and thus potentially increase the excitation efficiency. In this paper, a multiphoton microscopy system using a 12 fs Ti:Sapphire laser is reported. With adjustable dispersion pre-compensation, the pulse duration at the sample location can be varied from 400 fs to sub-20 fs. The efficiencies of TPEF and SHG are studied for the various pulse
durations, respectively. Both TPEF and SHG are found to increase proportionally to the inverse of the pulse duration for the entire tested range. To transmit most of the SHG and TPEF signals, the spectral transmission widow of the detection optics needs to be carefully considered. Limitation from phase-matching in SHG generation is not significant because the effective interaction length for SHG is less than 10 μm at the focal depth of the objectives. These results are important in improving MPM excitation efficiency using ultrashort pulses. MPM images from human artery wall are also demonstrated.
Properties of 3 types of multilayer dielectric chirped mirrors manufactured with Helios Leybold system (magnetron sputtering with plasma/ion assisted technology) are discussed. The first type includes mirrors providing negative group delay dispersion (GDD) and high reflectance in a wavelength range 650-1150 nm. Such mirrors are used in a broadband Ti:Sapphire oscillator for generating sub-6 femtosecond pulses. The second type of mirrors has extremely low both GDD oscillations and losses in a range 740-840 nm. Such mirrors are of interest for both long-cavity high-energy Ti:Sapphire oscillators and so-called external cavities for storing energy from femtosecond oscillators. The lowest residual GDD fluctuations achieved for this type of mirrors are 5 fs2. The third type is high reflectors with very high reflectivity. Different coating materials: Nb2O5, TiO2, Ta2O5 together with SiO2 are compared for these 2 types of mirrors. The results of reproducibility of such mirrors and their characterization in terms of reflectivity, losses, surface quality are presented. Comparison of the design with the manufactured mirror is also done.
A compact, low cost prismless Titanium:sapphire laser with 154nm bandwidth and 20mW output power was developed and ultrahigh resolution OCT ex vivo imaging in an animal model with sub-2μm and in vivo imaging in patients with 3μm axial resolution is demonstrated. This light source not only significantly reduces costs for broadband OCT light sources, but has also great potential for clinical OCT applications due to its small footprint (500x200mm including pump laser), user-friendliness and power stability.
By integration of a semiconductor mirror into a chirped mirror based Ti:Sapphire oscillator a very compact pulsed Terahertz source is demonstrated. Terahertz radiation is generated by a transient photocurrent in a LT-GaAs layer grown on a semiconductor saturable absorber mirror. This technique allows the manufacturing of ultra-stable, small-size (600 x 200 mm) and self-starting THz systems pushing forward the usability and availability for commercial pulsed Terahertz sources. The Terahertz spectrum goes up to 3 THz and average output power of about 7 μW is achieved.