H. Hundertmark

Supercontinuum generation with 200 pJ laser pulses in an extruded SF6 fiber at 1560 nm

We report an all-fiber diode-pumped Erbium-fiber oscillator-amplifier system as a source for supercontinuum generation in a photonic crystal fiber at 1560 nm. The passively mode-locked oscillator-amplifier system provides linearly polarized output pulses of 60 fs and an average output power of 59 mW at a repetition rate of 59.1 MHz. The laser pulses were launched into an extruded SF6-fiber for generation of an ultra-broadband supercontinuum. The evolution of the supercontinuum as a function of launched pulse energy was investigated. With pulse energies of about 200 pJ we observed a more than octave-spanning supercontinuum from 400 nm to beyond 1750 nm.

Phase-locked carrier-envelope-offset frequency at 1560 nm.

We report on the measurement of an Erbium-fiber oscillators carrier-envelope-offset frequency using an extruded SF6 photonic crystal fiber for the generation of a more than two octave-spanning supercontinuum from 400 nm to beyond 1750 nm. A modified type of f-2f-interferometer was employed, beating the frequency doubled input signal of the fiber oscillator with the supercontinuum to generate the carrier-envelope-offset beat. Controlling the fiber oscillators pump power with an electronic feedback loop, we phase-locked the carrier-envelope-offset frequency to an external reference source. The resulting residual phase excursions correspond to fractional frequency instabilities of the oscillators frequency comb of the order of 10(-16) for averaging times longer than 10 s.

Octave-spanning supercontinuum generated in SF6-glass PCF by a 1060 nm mode-locked fibre laser delivering 20 pJ per pulse

We report the generation of an octave-spanning supercontinuum in SF6-glass photonic crystal fiber using a diode-pumped passively mode-locked fs Yb-fiber laser oscillating at 1060 nm. The pulses (energy up to 500 pJ and duration 60 fs) were launched into a 4 cm length of PCF (core diameter 1.7 microm and zero-dispersion wavelength approximately 1060 nm). Less than 20 pJ of launched pulse energy was sufficient to generate a supercontinuum from 600 nm to 1450 nm, which represents the lowest energy so far reported for generation of an octave-spanning supercontinuum from a 1 microm pump. Since the laser pulse energy scales inversely with the repetition rate, highly compact and efficient sources based on SF6-glass PCF are likely to be especially useful for efficient spectral broadening at high repetition rates (several GHz), such as those needed for the precise calibration of astronomical spectrographs, where a frequency comb spacing >10 GHz is required for the best performance.

0.7 W all-fiber Erbium oscillator generating 64 fs wave breaking-free pulses

We report on the generation of wave breaking-free pulses from a passively mode-locked all-fiber Erbium oscillator at 1.55 microm pumped by a Raman fiber assembly operating at 1.48 microm. The extracted pulses show a self-similar behaviour and can be scaled up to an average power of 675 mW only limited by the pump power. The laser operates at the fundamental repetition rate of 108 MHz, therefore the pulse energy is 6.2 nJ. After external compression, the dechirped pulse duration is 64 fs.

Sub-85 fs mode-locked erbium fiber oscillator with tunable repetition rate

We present a sub-85 fs mode-locked erbium fiber oscillator with an average output power of 14 mW. The pulse repetition rate is tunable between 55.3 MHz and 56.4 MHz enabling improved applications in precision metrology at 1.55 /spl mu/m.

14 GHz visible supercontinuum generation: calibration sources for astronomical spectrographs

We report the use of a specially designed tapered photonic crystal fiber to produce a broadband optical spectrum covering the visible spectral range. The pump source is a frequency doubled Yb fiber laser operating at a repetition rate of 14 GHz and emitting sub-5 pJ pulses. We experimentally determine the optimum core diameter and achieve a 235 nm broad spectrum. Numerical simulations are used to identify the underlying mechanisms and explain spectral features. The high repetition rate makes this system a promising candidate for precision calibration of astronomical spectrographs.

Efficient all-diode-pumped double stage femtosecond optical parametric chirped pulse amplification at 1-kHz with periodically poled KTiOPO4

A practical efficient optical parametric chirped pulse amplification is demonstrated with periodically poled KTiOPO4. It provides a compact solution to amplify stretched pulses to the 100 µJ level (signal + idler) at 1 kHz. The amplified signal pulses near 1.57 µm are recompressed to 270 fs.

Spectral flattening of supercontinua with a spatial light modulator

We demonstrate the generation of broad spectra with a flat intensity distribution from originally highly structured supercontinua, obtained with femtosecond pulses in a photonic crystal fiber. This is accomplished by truncating the spectra at a constant level using a liquid crystal based spatial light modulator. The technique is useful for astronomical spectrograph calibration using frequency combs, where it allows to equalize the optical power of the calibration lines. This enables an improved calibration accuracy by maximizing each line’s signal-to-noise ratio.

Forward-Brillouin Scattering of Light at Acoustic Resonances in SF6 Glass PCF

Using a polarization-spectroscopy technique, we observe spontaneous forward Brillouin scattering of light in birefringent lead-silicate PCF. The higher stress-optical coefficient of the glass means that signals can be detected even in short lengths of fiber.

Influence of air-filling fraction on forward Brillouin scattering in highly birefringent PCF

In this paper, we report on the influence of cladding air-filling fraction on the spontaneous forward Brillouin spectrum in birefringent PCFs. We focused our investigation on a range of birefringent fibers drawn from the same fiber perform and showing roughly the same structure, but with different cladding air-filling fractions. To measure the spontaneous forward Brillouin scattering spectrum we launched light from a linearly polarized CW laser at 45deg with respect to the birefringence axis into 10 m long fibers. The polarization modulation induced by thermally excited phonons was measured using a polarization spectroscopy technique In addition to the experiments, we modelled the optical and acoustic modes of such fibers using a full-vectorial finite element approach. The ability to engineer the forward scattering spectrum by altering the cladding structure is important for the design of efficient acousto-optic devices and in reducing low frequency noise in quantum optics experiments.