T. Schlauch

Femtosecond passively modelocked diode laser with intracavity dispersion management

We report on the generation of ultrashort pulses by dispersion management of a passively modelocked external cavity diode laser. Pulse widths down to 200 fs are obtained at 830 nm emission wavelength. We use intracavity dispersion management to increase the spectral bandwidth and compress the strongly chirped pulses externally with a grating compressor.

All semiconductor high power fs laser system with variable repetition rate

Laser diodes offer an interesting alternative to commercially available light sources for the generation of ultrashort pulses. They have the unique feature that they can be directly electrically pumped and that the emission wavelength can be controlled over a huge spectral range by changing the composition of the laser material. Hence they have the potential of being a highly flexible, compact and cost effective light source. However there is a considerable chirp of the pulses generated by a diode laser as a consequence of the strong coupling of real and imaginary part of the susceptibility in the semiconductor. This problem is solved by using an external cavity with intracavity dispersion management. By applying this technique we are able to generate pulse durations with less then 200 fs if an additional external pulse compressor is used. By using such a cavity in a master oscillator power amplifier setup the peak power can be increased up to 6.5 kW. This enables a huge field of possible applications like time domain terahertz spectroscopy or material processing. Anyway for some applications like fluorescence lifetime imaging even the repetition rate of an external cavity laser is too high. To solve this problem an ultrafast semiconductor pulse picking element is implemented to reduce the repetition rate into the kHz region. In conclusion we will demonstrate a compact all semiconductor laser system which is capable to generate sub ps pulses with a high peak power and a variable repetition rate at central wavelength of approximately 840 nm.

THz sources and detectors based on diode lasers

We demonstrate concepts for compact and cost effective THz technology based on semiconductor diode lasers. In detail, we analyze diode laser based THz sources and detectors. Continuous wave THz radiation is generated by two color diode lasers either with external photomixers or direct difference frequency generation in the diode laser. For time domain THz sampling applications we present a suitable mode-locked diode laser system. Further we present a method to detect THz radiation with diode lasers at room temperature: A THz signal coupled into the active region of a diode laser results in a variation of the voltage across the p-n-junction.

Shoe box all semiconductor high power femtosecond laser system

Mode-locked laser diodes are attractive sources for the generation of ultra short pulses. These systems are particularly interesting as an alternative to conventional femtosecond lasers like Ti:sapphire lasers, which are rather complex and expensive. For example, a compact diode based system was already shown to replace successfully a Ti:sapphire laser in a Terahertz time-domain spectrometer [1].

Single-shot holography with colliding pulse mode-locked lasers as light source

So far, concepts for three dimensional biomedical imaging rely on scanning in at least one dimension. Single-shot holography [1], in contrast, stores three-dimensional information encoded in an electromagnetic wave scattered back from a sample in one single hologram. Single-shot holography operates with simultaneous recordings of holograms at different wavelengths. While the lateral sample information is stored in the interference patterns of individual holograms, the depth information is obtained from the spectral distribution at each lateral image point, similar to Fourier-domain optical coherence tomography [2]. Consequently, the depth resolution of the reconstructed image is determined by the bandwidth of the light source, so that a broadband light source is needed to obtain high depth resolution. Additionally, the holographic material, in which the holograms are stored, restricts the useable bandwidth. A thick photorefractive crystal can store several holograms of different wavelengths at once. As the crystal works best when using a source with a discrete spectrum, a light source is needed that has a spectrum with well distinguishable laser lines. In a proof-of-principle experiment, we use colliding pulse mode-locked (CPM) laser diodes [3] as light sources with a comb-like spectrum to demonstrate the concept of single-shot holography by storing multiple holograms at the same time in a photorefractive Rh:BaTiO3 crystal.

Passively mode-locked two section laser diode with intracavity dispersion control

Ultrashort laser pulses with a duration of 200 fs were obtained from a passively modelocked external cavity diode laser at 830 nm emission wavelength. By intracavity dispersion control the spectral bandwidth is increased and the emitted pulses are compressed externaly by a grating compressor. A tapered amplifier is used to achieve peak powers of up to 2.5 kW.

Colliding pulse mode-locked lasers as light sources for single-shot holography

So far, concepts for three dimensional biomedical imaging rely on scanning in at least one dimension. Single-shot holography1, in contrast, stores three-dimensional information encoded in an electro-magnetic wave scattered back from a sample in one single hologram. Single-shot holography operates with simultaneous recordings of holograms at different wavelengths. While the lateral sample information is stored in the interference patterns of individual holograms, the depth information is obtained from the spectral distribution at each lateral image point, similar to Fourier-domain optical coherence tomography2. Consequently, the depth resolution of the reconstructed image is determined by the bandwidth of the light source, so that a broadband light source is needed to obtain high depth resolution. Additionally, the holographic material, in which the holograms are stored, restricts the useable bandwidth. A thick photorefractive crystal can store several holograms of different wavelengths at once. As the crystal works best when using a source with a discrete spectrum, a light source is needed that has a spectrum with well distinguishable laser lines. In a proof-of-principle experiment, we use colliding pulse mode-locked (CPM)3 laser diodes as light sources with a comb-like spectrum to demonstrate the concept of single-shot holography by storing multiple holograms at the same time in a photorefractive Rh:BaTiO3 crystal.

Terahertz generation with an 830 nm all semiconductor femtosecond laser system

We present a THz time-domain spectrometer based on an 830 nm all semiconductor femtosecond laser system. Optical pulses with durations of less than 600 fs are used to gate standard LT-GaAs antennas. We achieve a signal to noise ratio of more than 40 dB in intensity and a bandwidth of 1.4 THz. Simulations based on the Drude-Lorentz model show a good agreement with the measured THz signals. Spectroscopic data on polymeric compounds and first THz images taken with our system will be presented as well.