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A dual-wavelength femtosecond laser pulse source and its application for digital holographic single-shot contouring are presented. The synthesized laser source combines sub-picosecond time scales with a wide reconstruction range. A center wavelength distance of the two separated pulses of only 15 nm with a high contrast was demonstrated by spectral shaping of the 50 nm broad seed spectrum centered at 800 nm. Owing to the resulting synthetic wavelength, the scan depth range without phase ambiguity is extended to the 100-microm-range. Single-shot dual-wavelength imaging is achieved by using two CMOS cameras in a Twyman-Green interferometer, which is extended by a polarization encoding sequence to separate the holograms. The principle of the method is revealed, and experimental results concerning a single axis scanner mirror operating at a resonance frequency of 0.5 kHz are presented. Within the synthetic wavelength, the phase difference information of the object was unambiguously retrieved and the 3D-shape calculated. To the best of our knowledge, this is the first time that single-shot two-wavelength contouring on a sub-ps time scale is reported.

Compression schemes for the generation of ultrashort laser pulses traditionally employ Kerr-based spectral broadening in a confined nonlinear geometry (photonic crystal fiber or hollow fiber) followed by an external dispersion compensation scheme. Circumventing the pulse energy limitation of traditional compression, filament self-compression has recently emerged as an alternative method [1,2]. In particular, this scheme does not require any further dispersion compensation after nonlinear propagation in the filamentary channel, a circumstance that is not fully understood theoretically at this point. In the following, we will discuss on-axis self-compression as arising from a self-induced spatial contraction of the pulsed laser beam, with only negligible longitudinal energy exchange and conventional pulse shaping action. In fact, the mechanism behind the novel compression scheme is found to show a resemblance with methods for compressing electric currents in so-called z-pinch discharges. These highcurrent discharges show some remarkable parallels to the nonlinear optical scenario of filamentary propagation. These include a Nonlinear Schrodinger Equation for the magnetic field, the formation of plasma filaments due to spatial break-up, and a self-induced pinching mechanism.

A novel method for contouring of optical surfaces with unprecedented dynamic range is presented. At an object depth ≫50 µm, surface deformations of a MEMS of some 10 nm are still unambiguously detectable.

A concept for orthogonal control of phase and group delay inside a laser cavity by a specially designed compensator assembly is discussed. Similar to the construction of variable polarization retarder, this assembly consists of two thin wedge prisms made from appropriately chosen optical materials. Being shifted as a whole, the assembly allows changing the phase delay with no influence on the cavity round-trip time, whereas relative shifting of the prisms enables adjustment of the latter. This scheme is discussed theoretically and verified experimentally, indicating a factor 30 reduction of the influence on the repetition rate compared to the commonly used silica wedge pair. For a 2pi adjustment of the carrier-envelope phase shift, single-pass timing differences are reduced to the single-femtosecond regime. With negligible distortions of timing and dispersion, the described compensator device greatly simplifies carrier-envelope phase control and experiments in extreme nonlinear optics.

We propose a novel method to directly extract the phase from spectral interferograms, without the need for digital signal processing. This method is demonstrated with single-shot measurement and stabilization of the carrier-envelope phase of a 3 kHz amplifier system. Our scheme allows for real-time monitoring of the carrier-envelope drift and an increased loop width for stabilization. We find that in our amplifier laser system fast carrier-envelope phase jitter is mainly inherited from the oscillator stabilization loop but we also find previously unreported indications for a rapid pulse-to-pulse jitter from the amplifier pump laser.

We observe fragmentation of ${\mathrm{H}}_{2}$ molecules exposed to strong laser fields into excited neutral atoms. The measured excited neutral fragment spectrum resembles the ionic fragmentation spectrum including peaks due to bond softening and Coulomb explosion. To explain the occurrence of excited neutral fragments and their high kinetic energy, we argue that the recently investigated phenomenon of frustrated tunnel ionization is also at work in the neutralization of ${\mathrm{H}}^{+}$ ions into excited ${\mathrm{H}}^{*}$ atoms. In this process the tunneled electron does not gain enough drift energy from the laser field to escape the Coulomb potential and is recaptured. Calculation of classical trajectories as well as a correlated detection measurement of neutral excited ${\mathrm{H}}^{*}$ and ${\mathrm{H}}^{+}$ ions support the mechanism.

Spatio-spectral and spatio-temporal transfer and intensity propagation of truncated ultrashort-pulsed Bessel-Gauss beams were investigated. Extended needle-shaped focal zones were generated using a compact setup with a reflective small-angle axicon and self-apodized truncation by an adapted aperture. Spectral maps of Bessel-Gauss beams were analyzed on the basis of higher order statistical moments. Compared to focused pulsed Gaussian beams with their spectrally dependent propagation, an ultrabroadband spatio-spectral transfer function was detected over Rayleigh ranges exceeding 10 cm. These results indicate favorable pseudo-nondiffracting characteristics not only from the point of view of spatial propagation but also with respect to the spectral and temporal stability.

A novel all-electronic scheme for real-time measurement and stabilization of the carrier-envelope phase of kHz pulse trains is demonstrated, revealing new insight into the pulse-to-pulse phase fluctuations of such lasers.

A linear optical method is demonstrated for extracting the carrier-envelope offset phase via the fringe visibility in a combined two-path multi-path interferometer. This method is applicable to a wider class of lasers than f-to-2f interferometry.

We propose and demonstrate a novel quasi-common-path variant of the f-to-2f interferometer that widely removes undesired residual phase drift from femtosecond pulse trains and improves the utility of stabilization schemes in frequency metrology and attophysics.

The method of equivalent layers is a commonly used technique for designing optical multilayer interference coatings. Herpin's theorem [C. R. Acad. Sci. 225, 182 (1947)] states that every symmetrical multilayer structure is equivalent, at one arbitrary wavelength, to a single homogeneous layer. The Herpin equivalent layer is described by two design parameters, the equivalent index and the equivalent thickness. Alternatively, we recently developed an exact coupled-mode analysis for the description of multilayer interference coatings composed of a symmetrical combination of layers. The design parameters of the coupled-mode theory are the exact coupling coefficient and the exact detuning coefficient. Recently we used this method in the design of chirped mirrors for dispersion compensation. We prove that the two methods are equivalent and derive relations that link the design parameters of both formalisms. By use of these relations it is possible to translate between the coupled-mode formalism and the method of equivalent layers. The simultaneous availability of both design methods gives a new perspective on the analytical design of optical interference coatings with challenging spectral response characteristics.

We numerically investigate the propagation of a self-compressed optical filament through a gas-glass-gas interface. Few-cycle light pulses survive a sudden and short order-of-magnitude increase of nonlinearity and dispersion, even when all conservative estimates predict temporal spreading or spatial breakup. Spatio-temporal distortions are shown to self-heal upon further propagation when the pulse refocuses in the second gas. This self-healing mechanism has important implications for pulse compression techniques handled by filamentation and explains the robustness of such sources., Comment: 4 Pages, 4 figures

A procedure for computation of the nonlinear refractive index of a gaseous medium from the intensity dependence of the ionization rate is reported. The ionization rate is calculated from Keldysh theory via a Kramers-Kronig transform. Peremolov-Popov-Terent'ev (PPT) theory is analyzed in the perturbative limit of multiphoton ionization for a completely analytical expression for the nonlinear refractive index. The method requires knowledge of only the particle density and the ionization energy of the gas. Example calculations are performed for the inert gases and compared to experimental data and atomic model calculations for the hyperpolarizability of the respective media. Excellent agreement between reference data and the computed values derived from the Kramers-Kronig transform is found in the visible and infrared spectral range. Additionally, higher-order nonlinear refraction is discussed.

Single-walled carbon nanotube saturable absorbers were designed and characterized (modulation depth

Self-compression of intense ultrashort laser pulses inside a self-guided filament is discussed. The filament self-guiding mechanism requires a balance between diffraction, plasma self-defocusing and Kerr-type self-focusing, which gives rise to asymptotic intensity profiles on axis of the filament. The asymptotic solutions appear as the dominant pulse shaping mechanism in the leading part of the pulse, causing a pinch of the photon density close to zero delay, which substantiates as pulse compression. The simple analytical model is backed up by numerical simulations, confirming the prevalence of spatial coupling mechanisms and explaining the emerging inhomogeneous spatial structure. Numerical simulations confirm that only spatial effects alone may already give rise to filament formation. Consequently, self-compression is explained by a dynamic balance between two optical nonlinearities, giving rise to soliton-like pulse formation inside the filament.

We report on double-chirped mirrors with custom-tailored dispersion characteristics over a bandwidth of 170 THz in the visible. The mirrors are used in a prismless compressor for a noncollinear optical parametric amplifier in the visible. The compressed pulses, characterized for the what is believed to be first time by use of the spectral phase interferometry for direct electric field reconstruction technique, display a nearly flat phase from 510 to 710 nm and have a duration of 5.7 fs.

We demonstrate the generation of sub-6-fs pulses centered at 405 nm by frequency doubling of 8.6-fs Ti:sapphire laser pulses. The frequency doubling is carried out in a nonlinearly chirped quasi-phase-matching grating fabricated in a lithium tantalate substrate. This device simultaneously provides frequency conversion and pulse compression of the positively prechirped fundamental pulses. The second-harmonic pulses are characterized in a cross-correlation setup, and their pulse shapes are retrieved by two iterative phase-reconstruction algorithms. The generated second-harmonic spectrum spans a bandwidth of 220 THz. To our knowledge, these are the shortest pulses ever generated in the blue spectral region.

Ultrabroadband pulses exhibit a frequency-dependent mode size owing to the wavelength dependence of free-space diffraction. Additionally, rather complex lateral dependence of the temporal pulse shape has been reported for Kerr-lens mode-locked lasers and broadband amplifier chains and in frequency-domain pulse shapers, for example. We demonstrate an ultrashort-pulse characterization technique that reveals lateral pulse-shape variations by spatially resolved amplitude and phase measurements by use of spectral phase interferometry for direct electric-field reconstruction (SPIDER). Unlike with autocorrelation techniques, with SPIDER we can obtain spatially resolved pulse characterization even after the nonlinear process. Thus, with this method the spectral phase of the pulse can be resolved very rapidly along one lateral beam axis in a single measurement.

Summary form only given. This paper reports continuous-wave (cw) and passive mode-locked laser operation of diode-pumped semiconductor disk lasers based on gain sections with step and graded index designs, each containing 6 InGaAs quantum wells. Mode-locked laser operation is achieved applying both structures, using a V-shaped cavity including a fast saturable semiconductor absorber mirror. Results show that the graded index structure exhibits clear advantages over the step index structure in cw-laser operation with respect to the saturation of the absorption. However, for mode-locked operation, shorter pulses are generated using the step index structure.

This paper demonstrates a fast Gabor transform, enabling SPIDER phase retrieval with live update rates of several Hertz. This method combines the processing speed of the Takeda algorithm with the enhanced robustness of wavelet-based phase retrieval. Moreover, this algorithm allows for adjustment of the aspect ratio of the Heisenberg box to match the spectral resolution of the SPIDER method, which further suppresses spurious phase ripple.

Saturable absorber mirrors (SAMs) have found widespread application in the generation of ultrashort optical pulses and are one of the driving forces behind the all-solid-state revolution in femtosecond optics. While the design of the absorption properties of SAMs and its influence on the stability of mode-locking has been thoroughly investigated in the recent years, its phase and dispersion properties have only found little attention. This paper disusses a resonant concept, simultaneously providing large amounts of saturable absorption and dispersion with unprecedented values up to the order of 0.01 ps . A theoretical framework for predicting the SAM properties from a few optical key properties is provided. Dispersive effects can also occur as a parasitic side effect in regular SAM designs. This aspect is addressed and designs which are particularly susceptible toward such unwanted effects are indicated.

In this paper we discuss the spatio-temporal structures of the self-compressed pulses, both experimentally and theoretically. Most of our experiments have been conducted with a Ti:sapphire amplifier system, delivering 45-fs pulses at up to 5 mJ pulse energy at a 1 kHz repetition rate. Pulses from this source are loosely focused into a gas cell, which is filled with a noble gas, typically argon or krypton at 0.3 to 0.5 atmospheres. With pulse energies of 1 mJ or more, a filament is formed inside the gas cell. This filament can extend up to 50 cm or more, which typically reflects optimum compression conditions. The resulting pulses are analyzed by spectral phase interferometry for direct electric-field reconstruction. Pulses as short as 7.4 fs have been measured at pulse energies of 2 mJ. The spectrum displays significant broadening into the blue, whereas only little broadening is observed in the red. For a deeper analysis of the spectro-temporal structure of the self-compressed pulses, we computed XFROG spectrograms from the experimental and numerical data.

We experimentally demonstrate a new generation of chirped mirrors designed for Brewster’s angle incidence. Dispersion oscillations are virtually eliminated and extremely clean 5.6-fs pulses are generated without adaptive compression. The novel chirped mirrors are generally applicable for various spectroscopic pulse requirements.

Supercontinuum white-light generation in optical fibers is a process that is known for its extreme sensitivity toward fluctuations of the input pulses, giving rise to a strong amplification of input noise. Such noise amplification has been recognized as a detrimental effect that prevents compression of the broad white-light spectra into a few-cycle pulse. Here, we show that the same effect can be exploited to amplify and recover faint modulation signals to an extent that seems impossible with any electronic method. We experimentally demonstrate the deterministic amplification of faint amplitude modulation signals by up to 60 dB. As we show from numerical simulations, this amplification process arises from the interaction dynamics between solitons and dispersive radiation in the fiber. The resulting all-optic signal restoration provides a new photonic building block that enables signal processing at virtually unlimited processing speeds.

Passive mode-locking of a Tm,Ho:KLu(WO(4))(2) laser operating at 2060 nm using different designs of InGaAsSb quantum-well based semiconductor saturable absorber mirrors (SESAMs) is demonstrated. The self-starting mode-locked laser delivers pulse durations between 4 and 8 ps at a repetition rate of 93 MHz with maximum average output power of 155 mW. Mode-locking performance of a Tm,Ho:KLu(WO(4))(2) laser is compared for usage of a SESAM to a single-walled carbon nanotube saturable absorber.

Third-order optical nonlinearities play a vital role for the generation and characterization of ultrashort optical pulses. One particular characterization method is frequency-resolved optical gating, which can be based on a large variety of third-order nonlinear effects. Any of these variants presupposes an instantaneous temporal response, as it is expected off resonance. In this paper we show that resonant excitation of the third harmonic gives rise to surprisingly large decay times, which are on the order of the duration of the shortest oscillator pulses generated to date. To this end, we measured interferometric third-harmonic frequency-resolved optical gating traces in TiO2 and SiO2, corroborating polarization decay times up to 6.5 fs in TiO2. This effect is among the fastest effects observed in ultrafast spectroscopy. Numerical solutions of the time-dependent Schrodinger equation are in excellent agreement with experimental observations. Our work (experiments and simulations) corroborates that a noninstantaneous polarization decay may appear in the presence of a 3-photon resonance. In turn, pulse generation and characterization in the ultraviolet may be severely affected by this previously unreported effect.

Femtosecond pump-probe studies at 1.5 μm of PbTe quantum dots in a glass matrix have revealed oscillations due to a spheroidal acoustic mode. The wavelength dependence of the observed frequencies indicates size selectivity. The frequency and damping of the mode as a function of wavelength agree with the predictions of an acoustic continuum model that suggests that the dominant damping mechanism is radiative loss from the dots to the surrounding glass.

Compact optical channel dropping filters incorporating side-coupled ring resonators as small as 3 /spl mu/m in radius are realized in silicon technology. Quality factors up to 250, and a free-spectral range (FSR) as large as 24 nm are measured. Such structures can be used as fundamental building blocks in more sophisticated optical signal processing devices.

We analyze pulse self-compression in femtosecond filaments, both experimentally and numerically. We experimentally demonstrate the compression of 45 fs pulses down to a duration of 7.4 fs at millijoule pulse energies. This sixfold compression in a self-generated filament does not require any means for dispersion compensation and is highly efficient. We compare our results to numerical simulations, providing a complete propagation model that accounts for full dispersion, pressure variations, Kerr nonlinearity and plasma generation in multiphoton and tunnel regimes. The equations are numerically integrated and allow for a quantitative comparison with the experiment. Our experiments and numerical simulations reveal a characteristic spectrotemporal structure of the self-compressed pulses, consisting of a compressible blue wing and an incompressible red pedestal. We explain the underlying mechanism that leads to this structure and examine the scalability of filament self-compression with respect to pulse energy and gas pressure.

The spectrum of a mode-locked laser consists of a comb of equidistantly spaced frequencies. This comb has only two degrees of freedom, its offset frequency at zero and the spacing of the teeth of the comb. While the spacing of the frequencies is simply determined by the repetition rate of the laser and can be relatively easily controlled, the offset frequency is governed by phase differences between the carrier and the envelope of the pulses during one round trip through the laser cavity. This carrier-envelope offset (CEO) phase is measured via heterodyning different harmonics of the mode-locked laser spectrum. In an unstabilized laser, this CEO phase exhibits very strong noise and can fluctuate several thousand radians in only one second. We provide an analysis of CEO phase-noise contributions and track their origin. The passive stability with respect to CEO fluctuations can be greatly improved by suitable cavity design, which greatly simplifies the stabilization of the CEO phase. Recent efforts on carrier-envelope stabilization are reviewed and some limitations are outlined.

In this contribution, we report on time-of-flight mass spectroscopy of C/sub 60/ fullerenes that have been investigated with intense fs laser radiation. Fullerenes are extremely interesting model systems for studying the dynamics of ionization and energy coupling in complex systems with many degrees of freedom. Ultrashort pulses with a duration as short as 8.5 fs have been focused on the molecular beam, resulting in laser intensities up to 5/spl times/10/sup 14/ W/cm/sup 2/. Using different pulse durations the electron-electron and electron-phonon coupling times have been mapped out.

We experimentally demonstrate a novel generation of chirped mirrors, resulting in the compression of extremely clean 5.6-fs pulses from a noncollinear optical parametric amplifier. These mirrors display much smaller phase ripple than previous design approaches.

We demonstrate a novel technique for pulse compression of few-millijoule pulses with shorter than 10 fs duration. Our technique relies on spectral broadening in a white-light filament generated in a noble gas. In this filament we observe self-compression of 45 fs pulses down to below 8 fs duration without the need for any additional dispersion compensation. Using input pulses of 5 mJ, we generate compressed pulses with up to 3.8 mJ pulse energy. Therefore this method is much more efficient than previously demonstrated compression schemes. The generated peak powers of more than 100 GW at a kilohertz repetition rate open up a perspective for compression of few-cycle pulses with energies well beyond the capacity of hollow-fiber compressors.

Using an anomalously dispersive microstructure fiber and two different saturable absorber mirrors at 1.06 mum, we demonstrate soliton-like 180-fs pulses in addition to 400-fs pulses with up to 0.1 nJ energy using only intra-fiber dispersion compensation.

We carefully compared pulse characterization methods for few-cycle pulses, using transform-limited sub-7-fs oscillator pulses and chirped amplified pulses. The non-iterative MEFISTO method is found capable of determining all major properties of these challenging test pulses.

Single-maximum nondiffracting beams were generated both, by truncating pulsed Bessel beams and with thin-film axicons. Negligible crosstalk is observed in arrays of needle-shaped beams over substantial distances, enabling applications in pulse diagnostics and multichannel processing.

Using a spatially encoded arrangement for SPIDER, we accurately measure ultra-broadband sub-10-fs pulses that can exhibit a modulated spectrum and space-time coupling. The intuitive interferograms can be acquired single shot and real time. © 2005 Optical Society of America.

Confinement of light to small volumes has important implications for optical emission properties: it changes the probability of spontaneous emission from atoms, allowing both enhancement and inhibition. In photonic-bandgap (PBG) materials1,2,3,4 (also known as photonic crystals), light can be confined within a volume of the order of (λ/2n)3, where λ is the emission wavelength and n the refractive index of the material, by scattering from a periodic array of scattering centres. Until recently5,6, the properties of two- and three-dimensional PBG structures have been measured only at microwave frequencies. Because the optical bandgap scales with the period of the scattering centres, feature sizes of around 100 nm are needed for manipulation of light at the infrared wavelength (1.54 µm) used for optical communications. Fabricating features this small requires the use of electron-beam or X-ray lithography. Here we report measurements of microcavity resonances in PBG structures integrated directly into a sub-micrometre-scale silicon waveguide. The microcavity has a resonance at a wavelength of 1.56 µm, a quality factor of 265 and a modal volume of 0.055 µm3. This level of integration might lead to new photonic chip architectures and devices, such as zero-threshold microlasers, filters and signal routers.

Novel types of thin-film microoptical components have been found very advantageous for beam shaping of high-power and ultrashort-pulse lasers. Measuring techniques, nonlinear optics, materials processing, and further advanced photonic applications, will benefit from specific advantages. Compared to conventional microoptics, low dispersion and absorption as well as added degrees of freedom in structure and functionality are accessible. Single or multilayer designs, spherical and non-spherical profiles, extremely small angles, and flexible substrates enable key components for the tailoring of lasers in spatial, temporal, and spectral domain at extreme parameters. By vacuum deposition and selective etching transfer, a cost-effective fabrication of single or array-shaped refractive, reflective, or hybrid components is possible. During the last decade significant progress in this field could be achieved. Including very recent applications for spatio-temporal shaping and characterization of complex and non-stationary laser fields, the state of the art is presented here. Particular emphasis is put on the generation of localized few-cycle wavepackets from Ti:sapphire laser beams by the aid of broadband microaxicons. Special microoptics are capable of transforming vacuum ultraviolet radiation. Wavefronts of strongly divergent sources can be analyzed by advanced Shack-Hartmann sensors based on microaxicon-arrays. Single-maximum nondiffractive beams are generated by different approaches for self-apodizing systems. Prospects for future developments, like robust multichannel information processing with arrays of self-reconstructing X-pulses, are discussed.

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic crystals. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices.

We report the first observation of subradiance in plasmonic nanocrystals. Amplitude- and phase-resolved ultrafast transmission experiments directly reveal the coherent coupling between surface plasmon polaritons (SPPs) induced by periodic variations in the dielectric function. This interaction results in the formation of plasmonic band gaps and coupled SPP eigenmodes with different symmetries, as directly shown by near-field imaging. In antisymmetric modes, radiative SPP damping is strongly suppressed, increasing the SPP lifetime from 30 fs to more than 200 fs. The findings are analyzed within a coupled resonance model.

We study with 10-fs light pulses the ultrafast dynamics of light transmission through plasmonic 2D- and lD-nanocrystals. Two interfering transmission channels are identified: ultrafast non-resonant transmission due to photon tunneling, and time-delayed resonant re-emission of surface plasmons.

We investigate the generation of white-light continua in a kagome lattice structure. The dependence on pump power, propagation length, and polarization state of both, pump and continuum radiation is analyzed.

Ultrashort-pulse single-maximum nondiffracting beams of microscopic radius and large axial depths are interesting for applications in nonlinear optics and spectroscopy, for acceleration and manipulation of particles, measuring techniques, materials treatment or information processing. Here we report on the experimental generation of such beams by self-apodized truncation of Bessel and pseudo-Bessel beams from a Ti:sapphire oscillator. Small angle operation was enabled by thin-film structures. To obtain self-apodization, the diameter of the truncating diaphragm was adapted to the first minima of Bessel distribution. The propagation of (a) Bessel beams of meter-range axial extension shaped by axicon mirrors, and (b) microscopic pseudo-Bessel beams of millimeter-range extension shaped by Gaussian-shaped microaxicon lenses was studied. In case (a), single-maximum beams of > 20 cm depth were produced. To generate comparable focal zones from Gaussian beams, a much larger distance (10x) is necessary, and axial stretching of spectrum destructs the temporal structure. In case (b), the focal zone length was increased by a factor of >5 compared to a Gaussian beam. Arrays of truncated Bessel beams were generated as well. The experimental results indicate that truncated Bessel beams enable more compact setups than corresponding Gaussian beams and are in particular advantageous for ultrashort pulses. Further improvements are possible by combining coherent addition in resonators with truncation outcoupling.

Multiphoton excitation of photosensitizers for laser induced fluorescence diagnosis (LIFD) and photodynamic therapy (PDT) of tumors has the advantage of greater tissue penetration due to the longer wavelength of irradiation. However, multiphoton LIFD and PDT are presently not clinically applicable as there are no applicators available for the delivery of the pulsed laser radiation to the operating room. As an approach, in this contribution the beam delivery through photonic crystal fibers has been investigated. Pulses of a Ti:sapphire laser of 100 fs pulse duration and an average power of 150 mW have been transported through such a fiber of 25 m length and the resulting pulses show the absence of nonlinear contributions but still a broadening of the pulse to 2 ps due to the dispersion of the fiber. It is planned to compensate this broadening by a grating in front of the fiber. Alternatively, the transport of laser radiation of 150 fs and 100 mW through a mirror-joint-arm used for conventional CO2 lasers has been tested showing no broadening of the laser pulses. Two-photon photodynamic activity of mTHPC-CMPEG4 shall serve as a test of the laser light transport system.

Analysis and investigations on carrier-envelope noise, generating mechanisms in mode-locked laser oscillators are discussed. Understanding of these mechanisms is an important prerequisite for building jitter-free clockworks for frequency metrology and applications in extreme nonlinear optics.

The generation of ultrafast optical pulses has always relied strongly on the capabilities of dispersion compensation schemes. Some recent advances into the sub-5-fs regime have only been possible by improved dispersion compensation, be it by using chirped mirrors [1-3], liquid-crystal phase modulators in a zero dispersion delay line [4-6], or Raman sideband generation [7, 8]. However, neither method has been demonstrated with spectra exceeding a bandwidth of one optical octave. Here we address a novel route towards compression of ultrabroadband continua, based on a new generation of chirped mirrors.

Chirped mirrors have significantly advanced femtosecond pulse generation. We provide an overview on the design of such mirrors and describe novel approaches towards the compression of octave-spanning spectra to a duration of few optical cycles.