W. Hodel

200-femtosecond pulses at 1.06 μm generated with a double-stage pulse compressor

Starting with 90-psec pulses of a Nd:YAG laser, 200-fsec pulses are generated in a double-stage fiber-grating-pair pulse compressor. This corresponds to a compression factor of 450. A peak power enhancement of 16.7 from 480 W to 8 kW is calculated. The experimental results agree well with theoretical predictions.

Experimental observation of the self-stabilization of a synchronously pumped dye laser

Abstract A passive stabilization technique for a synchronously pumped dye laser is demonstrated. Using a linear external cavity a minute fraction of the pulse is split off and superimposed back to the main laser pulse. Even an extremely weak feedback pulse — whose energy corresponds to that one of a few single photons — leads to the generation of nearly Fourier-transform limited pulses and to a drastic reduction of the high frequency components of the pulse energy fluctuations.

Numerical simulation of coherent photon seeding: A new technique to stabilize synchronously pumped mode-locked lasers

Abstract A new technique which we call “Coherent Photon Seeding” (CPS) for the generation of stable, ultrashort pulse trains in synchronously pumped mode-locked (SPML) lasers was reported previously. The basic idea of the method is to split off a tiny fraction of the laser pulse oscillating in the resonator and to superimpose it back onto itself slightly advanced in time. We confirm by numerical calculations that by this coherent seeding the deleterious influence of the spontaneous emission on the pulse profile of SPML lasers is removed. In agreement with the experimental observation the resulting pulses have a smooth gaussian-like shape and drastically reduced energy fluctuations. The study also provides a further understanding of the pulse structure generated by SPML lasers.

Limits to the amplification efficiency of ultrashort fundamental solitons using Er-doped fibers

Abstract We have studied the amplification characteristics of ultrashort fundamental solitons in Er-doped fibers by solving numerically an extended version of the nonlinear Schrodinger equation. The model takes into group velocity and higher order dispersion self phase modulation, Raman self scattering and the frequency dependent gain and phase shift induced by the amplifier. Our results show that efficient amplification of ps solitons is possible without severe pulse distortions. For sub-ps pulses, however, the soliton self frequency shift becomes distinctly gain enhanced and drastically limits the amplification efficiency.

Passive stabilization of a synchronously pumped mode-locked dye laser with the use of a modified outcoupling mirror

Recently a new passive stabilization technique for synchronously pumped dye lasers was reported that allows one to generate nearly transform-limited pulses. The idea of this technique is to split off an extremely small fraction of the laser pulse and to superimpose it back on itself slightly advanced in time. In these experiments the seeding pulse was provided by an external cavity, which led to an undesirable frequency hopping. Here we present a simple modification of an outcoupling mirror that integrates the generation of the seeding pulse into the main laser cavity. In this way frequency-stable, nearly transform-limited pulses are generated.

Nonlinear pulse distortion at the zero dispersion wavelength of an optical fibre

Abstract Pulse propagation at the zero dispersion wavelength of a standard optical fibre is investigated experimentally and theoretically. The respective results are in remarkably good agreement and demonstrate that the combined influence of third order dispersion and fibre nonlinearity leads to severe distortions of the pulse temporal and spectral profiles. Using a straightforward physical model an analytical expression is derived which allows to calculate the critical experimental parameters for which significant nonlinear pulse distortion occurs.

Chirped pulse amplification in Er-doped fibers

Abstract Efficient amplification of ultrashort pulses in Er-doped fibers is difficult to realise because of temporal and spectral distortions which result from the influence of the intrinsic fiber nonlinearities. Using numerical calculations we show that the deleterious influence of the fiber nonlinearities can be suppressed to a large extent by applying the chirped pulse amplification technique. Our results demonstrate that practically distortionless and highly efficient amplification of ultrashort pulses in fiber amplifiers can be achieved in this way.

High Power Light-Transmission in Optical Wavequides

Optical lightguides (fibers) allow to guide light in a flexible manner to a working area. Such lightguides are however enherently very narrow structures, which leads to extremely high intensities in the guides even for moderate powers. The limiting processes for undisturbed transmission are described and for a variety of parameters and situations the corresponding numerical values are given, as far as available. The high intensity processes recently led to several interesting new device-applications.

Experimental and numerical investigation of short pulse propagation and amplification around 1.3 μm in a Nd3+-doped fluoride fiber

Abstract We have investigated experimentally and theoretically the propagation and amplification characteristics of short optical pulses at λ ≈ 1.3 μm in a neodymium-doped fluorozirconate fiber. We have found that psec pulses (4 ps) with sub-nJ energies can be propagated and amplified without appreciable temporal and spectral reshaping. The propagation and amplification of sub-psec pulses (300 fs) of comparable energy, however, is significantly affected by the dispersive and nonlinear properties of the fiber. The interplay between dispersion and nonlinear effects leads to a power dependent pulse broadening which is more pronounced when the pulses are amplified. The experimental results are in good agreement with numerical simulations based on an extended version of the nonlinear Schrodinger equation. The comparison between experimental and numerical results allows to identify the pulse shaping mechanisms involved which is important in order to assess the potential of Nd 3+ -doped fluoride fibers as mode-locked fiber lasers and amplifiers.

Stable and widely tunable all-fiber Pr(3+)-doped cw laser system using fiber Bragg gratings.

A simple and strictly all-fiber 1300-nm cw laser is presented. It is tunable over 16 nm with 0.5-nm linewidth and several milliwatts of output power in the whole tuning range from 1292 to 1308 nm. The setup uses a fiber Bragg grating as a combined tuning element and narrow-band output mirror. The simplicity and stability of this system are due to the following two characteristics: First, polarization control is not necessary anywhere in the system, and second, a wavelength-selective system and a narrow-band mirror are combined into one novel fiber-optic element.