R. Paschotta

Noise-related resolution limit of dispersion measurements with white-light interferometers

This paper presents results of our detailed theoretical and experimental analysis of the relationship between the spectral resolution and the noise in the group-delay dispersion (GDD) data measured by scanning white-light interferometry. We demonstrate that the practically achievable spectral resolution is limited, because the standard deviation of GDD is proportional to the third power of inverse spectral resolution, and for a specified accuracy the required number of averages scales with the sixth power of inverse spectral resolution. The influence of experimental parameters such as spectral brightness, bandwidth of the light source, and detection noise is examined in detail.

Thermal effects in high-power end-pumped lasers with elliptical-mode geometry

We discuss in detail the effects of thermal lensing and thermally induced stress in end-pumped lasers with a strongly elliptical pump and laser mode and compare this situation with cylindrical rod geometries.

Frequency comb generation with 50-GHz channel spacing in the telecom C-band

We present a frequency comb with a spectral width of 43 nm at -20 dB. This comb was generated by spectrally broadening the output of an amplified 50-GHz Er:Yb:glass laser with a highly nonlinear fiber.

Passively mode-locked surface-emitting semiconductor laser with nearly 1 W average power

Summary form only given. We recently demonstrated for the first time passive mode locking of a vertical-external-cavity surface-emitting semiconductor laser (VEC-SEL). The device was pumped with a diode laser and mode-locked with a semiconductor saturable absorber mirror (SESAM) This technology is expected to lead to very powerful and compact pulsed sources, with multi-GHz repetition rates. Compared to previous results, we have now obtained a much higher average output power of 213 mW and at the same time a significantly reduced pulse duration of 3.2 ps. This amounts to a 20-fold enhancement of the peak power, which is now 30 W. Semiconductor laser sources have previously reached such power levels only with amplifier systems or with synchronous pumping of VEC-SELs, using a powerful mode-locked pump source. In edge-emitting semiconductor lasers the average and peak power is limited by the small mode area, which cannot be easily increased. With optically pumped VEC-SELs these constraints are eliminated, and much higher powers are possible with accordingly increased mode areas. Diffraction-limited output, as required for mode locking, is obtained with an external cavity.

Limits to the power scalability of high-gain optical parametric oscillators and amplifiers

Recent developments in high-gain optical parametric amplifiers (OPAs) and oscillators (OPOs) have led to interesting picosecond and femtosecond pulse sources with high average power in different wavelength regions. We have investigated this with a combination of analytical and numerical techniques. In this way we have identified a limit on the peak power, and this limit has already been reached in experiments. The limit arises from back conversion, i.e., sum frequency generation from signal and idler. Power limits for various constraints on beam quality (M/sup 2/) and conversional efficiency (/spl eta/) can be seen from the graphs.

Passively mode-locked diode-pumped surface-emitting semiconductor lasers

Summary form only given.We believe we demonstrate the first passively mode-locked surface-emitting semiconductor laser, using a semiconductor saturable absorber mirror (SESAM). We obtained 5-ps pulses with 15.3-mW average power and 2.5-GHz repetition rate or 12-ps pulses at 1.8 GHz with 40 mW. We anticipate that even multiwatt average powers should be achievable with our concept; more than 0.5 W has been demonstrated with a similar device in continuous wave operation. This potential arises from the fact that optically pumped semiconductor vertical-external-cavity surface-emitting lasers, in contrast to edge-emitting semiconductor lasers, allow one to scale up the mode area in order to generate a high average power and high pulse energy, while the external cavity enforces a diffraction-limited output. Multi-GHz repetition rates without Q-switching instabilities are possible. In addition, the broad amplification bandwidth should be sufficient for pulse durations in the subpicosecond regime.

Femtosecond microjoule pulses with 15.8 W average power from a passively mode-locked diode-pumped Yb:YAG thin-disk laser

Summary form only given. Femtosecond laser sources with multi-watt average powers and multi-kW peak powers are required for many applications. We have found a power-scalable concept to achieve this kind of performance directly with a diode-pumped passively mode-locked laser oscillator, not requiring any amplification stages. The concept is based on a Yb:YAG thin-disk laser, which in continuous wave (CW) operation has delivered output powers of up to /spl ap/100 W in a diffraction-limited beam. We have now for the first time to our knowledge passively mode-locked such a laser using a semiconductor saturable absorber mirror (SESAM). The laser head, which had generated 20 W CW near-room-temperature produced 680-fs pulses at 1030 nm with 15.8 W of average power in two nearly transform-limited beams (time-bandwidth product 0.33). This is to our knowledge the highest average power reported for a laser oscillator (without amplifier) in the subpicosecond regime. The pulse repetition rate was 15 MHz. Pulse energies of 2/spl times/0.5 /spl mu/J and peak powers as high as 2 X 680 kW were achieved. Autocorrelation and optical spectrum are given. To obtain subpicosecond pulse durations, we operated the laser in the soliton mode-locked regime using a Gires-Tournois Interferometer (GTI). The high tendency of Yb:YAG for Q-switched mode-locking was strongly suppressed by the small laser mode size in the thin-disk laser head, the low repetition rate, and a stabilizing effect resulting from soliton mode-locking.

Novel 10- to 40-GHz Telecom Pulse Generating Sources with High Average Power

As data transmission rates continue to increase, pulsed lasers are becoming increasingly important for telecom applications. Novel transmission systems at 10 Gb/s and higher often use return-to-zero (RZ) formats [1,2] and soliton dispersion management techniques [3, 4], which both rely on clean optical pulses. Therefore, these approaches benefit greatly from the availability of simple, compact, and efficient optical pulse generators. There are many compelling reasons to use a pulsed laser directly as a source in the transmitter of optical telecommunication systems, rather than an externally modulated continuous-wave (cw) source. First, they eliminate the need for a high-end modulator to create the pulses and thereby simplify system architecture, increase efficiency, and reduce cost. Secondly, the contrast ratio of pulsed lasers is typically much higher than for modulated cw sources. This improves system signal-to-noise and allows further scaling to higher repetition rates through optical time-division multiplexing (OTDM). Apart from the transmitter side, there are interesting applications of pulsed lasers also in the receivers of transmission systems, e.g. for demultiplexing and clock recovery [5-7]. Furthermore, applications outside the telecom area, in the fields of optical clocking [8, 9], high-speed electro-optic sampling [10,11], frequency metrology (similar to the work presented in Ref. 12) or generation of polarized electron beams for particle accelerators 13 become increasingly important.

Passively mode-locked high-power lasers and femtosecond high-power nonlinear frequency conversion

We report on passively mode-locked think disk lasers with up to 60 W average power, nonlinear pulse compression to 33 fs with 18 W average power, and a fiber-feedback parametric oscillator generating 15 W in the 1.5-μm region.

Mode-locked high-power surface-emitting semiconductor laser

We report an optically pumped surface-emitting semiconductor laser which is passively mode-locked and generates 1.9 W of average power in 27-ps pulses at 0.96 /spl mu/m. The maximum diffraction-limited continuous-wave output is 4.4 W.We report an optically pumped surface-emitting semiconductor laser which is passively mode-locked and generates 1.9 W of average power in 27-ps pulses at 0.96 /spl mu/m. The maximum diffraction-limited continuous-wave output is 4.4 W.