Wolfgang Seitz

Broadly tunable dual-wavelength light source for coherent anti-Stokes Raman scattering microscopy

The signal and idler beams from a picosecond, synchronously pumped optical parametric oscillator (OPO) provide the two colors necessary for coherent anti-Stokes Raman scattering (CARS) microscopy. The OPO provides a continuously tunable frequency difference between the two beams over a broad range of Raman shifts (100-3700 cm(-1)) by varying the temperature of a single nonlinear crystal. The near-infrared output (900-1300 nm) allows for deep penetration into thick samples and reduced nonlinear photodamage. Applications of this light source to in vivo cell and ex vivo tissue imaging are demonstrated.

Continuum generation in a novel photonic crystal fiber for ultrahigh resolution optical coherence tomography at 800 nm and 1300 nm

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.

Quasisynchronous Pumping of Mode-locked Few-cycle Titanium Sapphire Lasers

We investigate the modelocking dynamics of quasi-synchronously pumped, dispersion managed Kerr-lens modelocked Titanium-Sapphire lasers. For the first time, self-starting few-cycle laser pulses with 6 fs pulse duration and ultrabroadband optical spectra are demonstrated without using any intracavity elements like saturable absorbers.

All-optical active mode locking with a nonlinear semiconductor modulator

All-optical active mode locking of a picosecond Nd:YVO(4) laser is demonstrated by use of an intracavity semiconductor nonlinear Fabry-Perot mirror. The reflectivity of the Fabry-Perot mirror is modulated by optical carrier injection. Depending on the carrier recombination time, the width of the Nd:YVO(4) laser pulses varies from 6 to 20 ps, as is typical for passively mode-locked Nd:YVO(4) lasers.

All-optical synchronization and mode locking of solid-state lasers with nonlinear semiconductor Fabry-Perot mirrors

The dynamics of laser oscillators can be directly accessed by modulating the intracavity losses. The authors present a new approach of optically driven loss modulation by means of a nonlinear semiconductor mirror based on a Fabry-Pe/spl acute/rot structure [Fabry-Pe/spl acute/rot modulator (FPM)]. The modulation depth of this device can be several percent and the response time is dominated by the recombination time of the generated free carriers inside the semiconductor, which can be reduced by ion implantation. This paper reviews the design of the FPMs and their optical characterization via spectrally resolved two-color pump-probe spectroscopy. Applications of the FPM are the synchronization of the pulse trains of independent mode-locked laser oscillators. The authors demonstrate the synchronization of a ps-Nd:YVO/sub 4/ laser to a fs-Ti:sapphire laser in a master-slave configuration and show experiments on the carrier-envelope phase relationship between the two synchronized pulse trains. Finally, they show that it is possible to actively mode lock a solid-state laser by an optically driven FPM. The resulting pulsewidths of the actively mode-locked Nd:YVO/sub 4/ laser are as short as 6 ps, which is comparable to passively generated pulses.

New ultrafast high-energy laser concepts and their applications

Ultrafast laser systems with pulse durations in the femto-and picosecond regime have proven their potential in several material processing applications. So far, a lot of these applications have been limited by the costly and difficult operation of the laser systems. We report on a new generation of powerful ultra-compact laser oscillators combining ’cavity - dumping’ with the proven techniques of direct diode-pumping and passive semiconductor saturable absorber mirror (SESAM) modelocking. Without using complex amplifier schemes these lasers generate femto-and picosecond short pulses with energies in the µJ range at tunable repetition rates up to 1 MHz. We demonstrate the use of the laser for fabrication of photonic devices in bulk glass. The combination of high pulse energies at high repetition rates together with a short pulse duration and good beam quality opens up new dimensions in high speed micro processing.Ultrafast laser systems with pulse durations in the femto-and picosecond regime have proven their potential in several material processing applications. So far, a lot of these applications have been limited by the costly and difficult operation of the laser systems. We report on a new generation of powerful ultra-compact laser oscillators combining ’cavity - dumping’ with the proven techniques of direct diode-pumping and passive semiconductor saturable absorber mirror (SESAM) modelocking. Without using complex amplifier schemes these lasers generate femto-and picosecond short pulses with energies in the µJ range at tunable repetition rates up to 1 MHz. We demonstrate the use of the laser for fabrication of photonic devices in bulk glass. The combination of high pulse energies at high repetition rates together with a short pulse duration and good beam quality opens up new dimensions in high speed micro processing.

Carrier-envelope phase dynamics of all-optically synchronized mode-locked lasers

The mode-combs of a femtosecond Ti:sapphire- and a picosecond Nd:YVO/sub 4/ laser are fully characterized by measuring the carrier-envelope offset frequencies of the lasers via interference at the spectral overlap and at different harmonics, respectively.

Intracavity Fabry-Perot-modulator: Characterization and modelling

Summary form only given. Modulation of intracavity losses is a powerful tool for controlling the laser dynamics, e.g. for active mode-locking and for synchronization of different lasers. In this paper we present an optical device that allows for fast modulation of the intracavity losses by external illumination. The device is designed as a nonlinear semiconductor Fabry-Perot etalon consisting of two Bragg reflectors with a center wavelength of 1064 nm at the backside and the frontside of a 5-/spl mu/m-thick nonlinear medium - an InGaAs layer. The indium content is chosen such that the bandgap energy is 1.28 eV (/spl lambda//sub gap/ = 970 nm). While the device is highly reflecting for wavelengths longer than /spl lambda//sub gap/ around 1064 nm, radiation with /spl lambda/ < /spl lambda//sub gap/ generates carriers which change the index of refraction and, therefore, the reflectivity of the device in the vicinity of a Fabry-Perot resonance. To characterize the capabilities of the optically controlled Fabry-Perot-modulator (FPM), we performed a spectrally resolved two color pump probe measurement.

All optical passive synchronization of two independent laser oscillators

Summary form only given. A novel scheme for passive synchronization of two independently mode-locked laser oscillators in a master slave configuration is presented. As an example the scheme is used to synchronize a picosecond mode-locked Nd:YVO/sub 4/ laser (at 1064 nm) as the slave and a femtosecond mode-locked Ti:sapphire laser (around 850 nm) as the master oscillator. All optical synchronization is achieved by modulating the intracavity losses of the slave laser with the pulse train of the master oscillator.

Passive synchronization of two independent laser oscillators with a Fabry-Perot modulator

By optical modulation of the reflectivity of an intracavity nonlinear Fabry-Perot semiconductor mirror, the pulse train from a passively mode-locked picosecond Nd:YVO(4) laser oscillator is synchronized to an independent femtosecond-mode-locked Ti:sapphire laser. We obtain stable synchronized pulse trains at central wavelengths of 1064 and 850 nm, and the Ti:sapphire laser is still independently tunable over a large wavelength range. The tolerable cavity-length difference between the two laser oscillators exceeds 20mu;m .