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We demonstrate a frequency quadrupled soliton self-frequency shifted femtosecond fiber laser with multiple tunable outputs in the near infrared and blue spectral range providing up to 120fs and 6nJ pulse energy.

2-Photon laser scanning microscopy (TPLSM) is often used for chronic in vivo studies. Small deviations in the sample orientation, however, make comparison of three-dimensional image stacks taken at different time-points challenging. When analysing changes of three-dimensional structures over time (4D imaging) this fundamental problem is one of the main limitations when complex structures are studied repetitively. We used an upright two-photon microscope complemented with a software-controlled stage-rotation instead of a conventional stage for chronic in vivo imaging in the brain of transgenic mouse models of Alzheimer's disease. Before every session an optimal imaging condition was successfully created by aligning the surface of the cranial window perfectly perpendicular to the laser beam. Deviations in the sample orientation between consecutive imaging sessions could be eliminated which improves conditions for chronic in vivo studies.

We present an electrooptic (EO) terahertz imaging technique providing a demodulating detector array for phase-sensitive multipixel terahertz detection. The terahertz radiation from a quartz-stabilized microelectronic emitter is mixed with the synchronized laser beat signal of a continuous-wave distributed-feedback diode laser pair. A fast laser current control loop provides stable phase locking between the terahertz emitter and the laser difference frequency, whereby a demodulating near-infrared photonic-mixer-device camera is used for depth-resolving EO terahertz imaging. Alternatively, a femtosecond laser is used for the EO read-out.

Femtosecond lasers belong to the most exciting kind of lasers. They are used in science, medicine and industry where their light serves for example as optical probe for time-resolved studies, the analysis of biological material or the micro structuring of advanced material components.

Die moderne optische Mikroskopie und die Lasertechnik sind eng miteinander verzahnt. Im Unterschied zur klassischen Lichtmikroskopie, in der fur die uberwiegende Zahl von Untersuchungen noch traditionelle, inkoharente Lichtquellen eingesetzt werden, dominiert in der konfokalen Mikroskopie langst der Laser. Hier liegt das Hauptinteresse vor allem in der dreidimensionalen Untersuchung von Proben im Bereich Biotechnologie und Life Science.

We present difference-frequency stabilization of free-running distributed-feedback (DFB) diode lasers, maintaining a stable phase-lock to a local oscillator (LO) signal. The technique has been applied to coherent hybrid THz imaging which employs a high-power electronic radiation source emitting at 0.62 THz and electro-optic detectors. The THz radiation of the narrow-band emitter is mixed with the difference frequency of the DFB diode laser pair. The resulting intermediate frequency is phase-locked to the LO signal from a radio-frequency generator using a fast laser-current control loop. The stabilization scheme can be adapted readily to a wide range of applications which require stabilized laser beat-notes.

We report on the frequency doubling of an Erbium-doped master-oscillator power-amplifier system. The fundamental 72 fs pulses at a wavelength of 1.56 µm are frequency doubled to 780 nm and compressed in a Gires-Tournois-interferometer mirror pair to a duration of 55 fs with an average power of 172 mW with an efficiency of 48 %. To our knowledge these are the shortest pulses ever reported from a frequency-doubled fiber-laser system.

We present a heterodyne hybrid terahertz imaging system, which combines electronic narrow-band emitters, operating at 0.2 THz and 0.62 THz respectiveley, with a continuous-wave two-color laser system for electro-optic detection. The laser system employs two distributed-feedback laser diodes, providing a tunable difference frequency which is phase-locked to the emitted terahertz frequency with an offset of 10 MHz.

A frequency-quadrupled fiber-amplified semiconductor master oscillator provides 32mW tunable CW power at the 281.6 nm clock transition of 119Hg+. Master-line width and tuneability are maintained for the UV light while amplifier added background is suppressed.

Terahertz radiation bears great potential in imaging and spectroscopy. One established method of generating tunable continuous-wave (cw) terahertz light is optical heterodyning: a photomixer is irradiated with two near-infrared lasers of adjacent wavelengths, and an antenna emits an electromagnetic wave at the terahertz difference frequency [1]. We developed an all-fiber-based cw terahertz spectrometer, which combines distributed feedback (DFB) diode technology and precise interferometric frequency control. This allows us to stabilize the laser frequency to arbitrary values within the diode's tuning range, achieving a frequency resolution on the 1 MHz level and a long-term stability of about 20 MHz, yet maintaining a tuning range of ≫ 1 THz.

We realized a tunable continuous-wave terahertz (cw THz) source with MHz frequency resolution. The system is based on optical heterodyning of two near-infrared Distributed Feedback (DFB) diode lasers, each laser being stabilized by electronic feedback from a low-finesse quadrature interferometer. The control loop permits precisely linear laser frequency scans over >1200 GHz, and a beat signal linewidth of 1 MHz @ 80 ms time scale. Using GaAs photomixers and log-periodic antennae, we achieve an SNR of the THz power of > 70 dB at 100 GHz and 100 ms integration time, and still ~ 30 dB @ 1 THz. As an example for high-resolution THz spectroscopy, we characterize the transmission properties of a sub-wavelength metal grating.

We demonstrate a hybrid system for THz raster scan imaging using frequency-stabilized DFB lasers for electro-optic detection. The system combines a 0.65-THz micro-electronic narrow-band emitter with two synchronized diode lasers, providing two-color laser radiation. The functional principle promises three-dimensional real-time imaging capabilities.

We demonstrate the use of two ultrafast fiber laser systems locked together at identical repetition rates of 100 MHz to achieve a timing resolution below 300 fs for pump-probe experiments. By sweeping the set-point of the locking electronics, we scan the time delay between the individual pulse trains by 800 ps. This scanning technique requires only sub-micrometer mechanical motion. Since the temporal scan range is determined electronically, the acquisition can be limited to regions where meaningful physical data is recorded. We discuss how our technique can approach asynchronous optical sampling based on GHz repetition rate lasers in terms of data collection efficiency while offering a number of practical advantages.

In the last decades, diode laser systems conquered the spectral range step-by-step from conventional gas lasers, wherever they can match or outperform in optical specifications. Although highly anticipated in the ultraviolet wavelength range, for instance in high-resolution lithography, biological and medical fluorescence applications or holography, cw single frequency operation of sufficient power has been a challenge for diode or other solid state laser systems. Currently this scope is still dominated by the HeCd gas laser, emitting at 325 nm with powers of up to 100 mW. In this paper we present a diode laser system emitting at 325 nm offering the same output power by efficient second harmonic generation (SHG) of a master oscillator power amplifier (MOPA) at 650 nm. For the master oscillator a ridge waveguide diode is anti-reflection coated and used in an external cavity diode laser (ECDL) with grating feedback in Littrow configuration. This setup features a MHz line width (coherence length of 100m), a coarse tuning range from 649 nm to 657 nm and a mode hope free tuning of 20 GHz. In a second step, we use a tapered amplifier to boost the output from the ECDL to a level of 400 mW, for powering an efficient second harmonic generation process in an enhancement cavity. Faraday isolators on both ends of the amplifier stage prevent back reflection and stabilize the single mode operation of the system. Together with astigmatism compensation this yields to a high spatial quality (M 2

A master oscillator power amplifier system operating around 670 nm is presented. For the master laser an external cavity diode laser is used with an output power of 25 mW at tunable wavelength and with narrow line width. A tapered amplifier boosts the power up to 970 mW while maintaining the spectral characteristics and keeping the beam quality close to the diffraction limit. The performance of the laser system is presented and a Lithium spectrum depicting the suitability of the system for Lithium spectroscopy, cooling and trapping.

High-brightness tapered lasers and amplifiers at 670 nm with output powers up to 1 W and nearly diffraction limited beam quality were realised. The devices consist of a 750 µm long straight section and a 1250 µm long tapered section. Devices with a taper angle of 2°, 3° and 4° were manufactured. The material quality was studied in a long-term test for ridge-waveguide lasers. Devices with 7.5 µm ridge width show reliable operation at 100 mW output power over more than 10000 h. At a temperature of 15°C a tapered lasers with an angle of 4° reached an output power of 1 W at a current of 2.1 A. The highest conversion efficiency for this device was 24%, the peak wavelength of the emission was 668 nm and the spectral width was smaller than 0.2 nm. The beam propagation factor was M 2 = 1.7 (1/e 2 ) and M 2 = 3.0 (second moments). At 500 mW output power, master-oscillator power-amplifier (MOPA) devices showed also a nearly diffraction limited beam quality with M 2 < 1.5 and reliable operation with degradation rates as low as 7x10 -6 h -1 over 1200 h. The spectral line-width in this arrangement is determined by the master oscillator and is suitable for high-resolution spectroscopy.

We compare two methods for the generation of light pulses across the visible spectral band starting from a 1.55 mum fiber laser. Particular advantages of either technique are discussed with respect to applications in frequency metrology and microscopy.

Distributed feedback (DFB) laser chips have recently become available at wavelengths that match the D1 and D2 resonance transitions of alkaline atoms. We investigated the spectral properties, tuning characteristics and modulation behavior of continuous wave, single-mode DFB diodes at 778-780 nm and performed high-resolution spectroscopy of Rubidium vapor. The mode-hop free tuning range of the DFB diodes was as large as 2.4 nm (1186 GHz). The line width of the laser diodes was examined both with a heterodyne beat experiment and with high-resolution Doppler-free two photon spectroscopy, yielding a half width of 2-2.5 MHz. The saturation spectra of the D2-line of 85Rb and 87Rb were recorded with a resolution close to the natural line width. The emission frequency was actively stabilized to Doppler-free transitions with a relative accuracy of better than 4 parts in 109 using commercially available servo devices only. The output power of 80 mW was sufficient to allow for two photon spectroscopy of the 5S-5D-transition of 87Rb. We conclude that the performance of the DFB laser equals that of grating-stabilized external-cavity diode lasers (ECDLs), without the mechanical complexity of the latter systems. The DFB diode is thus well-suited to high-resolution applications in alkaline spectroscopy, including laser cooling and optical manipulation of ultra-cold atoms.

Gain-switching of laser diodes might be the most convenient way to generate picosecond laser pulses. The outstanding features of gain-switched laser diodes are a rich choice of wavelength and an easy synchronization to an external trigger source. To broaden the field of applications we pushed the peak power to the 10 W level while maintaining the essential characteristics of the laser source. In a master oscillator power amplifier (MOPA) configuration a tapered amplifier is used to increase the output from 10 mW to 160 mW average power. Second harmonic generation is demonstrated in a single pass setup, which results in 6.5 mW average power at 532 nm with a repetition rate of 80 MHz.

Frequency conversion of near-infrared diode lasers provides an efficient method to generate tunable laser radiation in the near-UV, violet and blue-green spectral range. High-power, coherent fundamental laser sources such as master oscillator-power amplifier (MOPA) configurations are now state of the art and commercially available. A new, highly efficient material for second-harmonic generation (SHG) is Bismuth Triborate ("BiBO", stoichiometry BiB3O6). The material has a high effective non-linearity d eff , is non-hygroscopic and transparent for wavelengths between 286 nm and 2.5 μm. Compared to other non-linear crystals, "walk-off" effects between fundamental laser radiation and frequency-doubled beam are considerably lower. We used a BiBO crystal in a resonant doubling cavity to convert the output of a 780 nm, 900 mW tapered amplifier system. A maximum UV power of 400 mW (conversion efficiency 44%) was attained. This value is 3-4 times higher than previous results obtained with LBO or BBO crystals and, to the best of our knowledge, represents the highest tunable cw power of a frequency-converted diode laser.

Ultra-high bandwidth continuum generation has been attracting enormous interest for applications in optical frequency metrology, low-coherence tomography, laser spectroscopy, dispersion measurements, sensor techniques and others. The acceptance of this new technology would greatly benefit from the availability of compact and user-friendly sources. High index planar devices provide a versatile and unique approach to continuum generation. The dispersion can be carefully engineered by choosing the material and the geometry of the waveguides. Optical integration can also be provided on the same platform. Hundreds of different waveguides having different and calibrated dispersions can be integrated in few tens of millimeters. Input and output of the 2D guides can be tailored to provide mode matching to fibers and pump lasers by means of single element bulk optics. In this paper for the first time we demonstrate a low-noise, ultra-high bandwidth continuum at 1.55 μm. A bandwidth in excess of 390 nm is obtained by launching energy as low as 50 pJ in a 12 mm short tapered planar waveguides. The pump wavelength was in the normal dispersion regime and was provided by a compact, fiber-based sub-100 femtosecond source.

Mode-locked Er-doped fiber laser systems built on single-mode fiber technology continue to see a remarkable improvement in their performance characteristics. In this contribution, we present an extremely compact and powerful version of such a laser source, delivering elevated peak powers well in excess of 10 kW in combination with ultrashort pulse durations below 100 fs. Eliminating the need for costly pump sources, external cooling as well as daily re-alignment routines, this laser system opens possibilities for an entirely new class of experiments and applications to a much larger group of users than only dedicated laser institutes. The accessible wavelength range is greatly enhanced by generation of a supercontinuum inside an integrated highly nonlinear fiber. We report output spectra with a bandwidth exceeding one full octave which we utilize for phase stabilization of the laser source. As a first proof of principle, a precise frequency measurement is carried out on a cavity-stabilized diode laser over a time interval of 88 hours without interruption. With regard to the time domain pulse structure, the user can select to re-compress defined parts of the continuum to achieve pulse durations below 30 fs. At the same time, the central wavelength of these pulses is easily shifted over a wavelength interval from 1130 nm to 1400 nm. Based on these findings, we demonstrate the generation of widely tunable light pulses in the visible spectral range by efficient frequency doubling. Potential applications for this novel light source are discussed.

We realized a tunable continuous-wave terahertz source with megahertz frequency resolution. The system is based on optical heterodyning of two near-infrared distributed feedback diode lasers, each laser being stabilized by electronic feedback from a low-finesse quadrature interferometer. The control loop permits precisely linear laser frequency scans over >1200 GHz, and a beat signal linewidth of 1 MHz at 80 ms time scale. Using GaAs photomixers and log-periodic antennae, we achieve a signal-to-noise ratio of the terahertz power of >70 dB at 100 GHz and 100 ms integration time, and still approximately 30 dB at 1 THz. As an example for high-resolution terahertz spectroscopy, we characterize the transmission properties of a subwavelength metal grating.