Bojan Resan

Dispersion managed semiconductor mode-locked ring laser

A novel breathing-mode external sigma-ring-cavity semiconductor mode-locked laser is developed. Intracavity pulse compression and stretching produce linearly chirped pulses with an asymmetric exponential temporal profile. External dispersion compensation reduces the pulse duration to 274 fs (within 10% of the bandwidth limit).

Dispersion-managed breathing-mode semiconductor mode-locked ring laser: experimental characterization and numerical simulations

A dispersion-managed breathing-mode mode-locked semiconductor ring laser is studied. The working regime and pulse evolution at the key cavity points are experimentally characterized and numerically simulated. Linearly chirped, asymmetric exponential pulses are generated and externally compressed to 274 fs, which is within 10% of the bandwidth limit. The close agreement between the simulated and the measured results verifies our ability to control the physical mechanisms involved in pulse formation and shaping within the ring cavity.

FROG measured high-power 185-fs pulses generated by down-chirping of the dispersion-managed breathing-mode semiconductor mode-locked laser

A dispersion-managed breathing-mode mode-locked semiconductor ring laser generates linear down-chirped pulses which are dispersion compensated to duration as short as 185 fs and characterized by second-harmonic generation frequency-resolved optical gating. Down-chirping when compared to up-chirping allows broader mode-locked spectra and shorter pulse generation owing to the temporal and spectral semiconductor gain dynamics. The measured average output power is 14 mW at 323-MHz pulse repetition rate, implying a peak power of /spl sim/230 W, and a focused intensity of /spl sim/4.6 GW/cm/sup 2/. To our knowledge, this is the highest peak power and the shortest pulse generation from an electrically pumped all-semiconductor system, obtained only by linear chirp compensation.

Two-photon fluorescence imaging with 30 fs laser system tunable around 1 micron.

We performed high signal-to-noise ratio TPF imaging of mouse intestine with a laser system exhibiting 30 fs tunable within 800-1200 nm, 50 mW average power, based on a compact Yb-doped laser seeding a microstructured fiber.

Yb:YAG single-crystal fiber amplifiers for picosecond lasers using the divided pulse amplification technique

A two-stage master-oscillator power-amplifier (MOPA) system based on Yb:YAG single-crystal-fiber (SCF) technology and designed for high peak power is studied to significantly increase the pulse energy of a low-power picosecond laser. The first SCF amplifier has been designed for high gain. Using a gain medium optimized in terms of doping concentration and length, an optical gain of 32 dB has been demonstrated. The second amplifier stage designed for high energy using the divided pulse technique allows us to generate a recombined output pulse energy of 2 mJ at 12.5 kHz with a pulse duration of 6 ps corresponding to a peak power of 320 MW. Average powers ranging from 25 to 55 W with repetition rates varying from 12.5 to 500 kHz have been demonstrated.

Sub-100 fs high average power directly blue-diode-laser-pumped Ti:sapphire oscillator

Ti:sapphire oscillators are a proven technology to generate sub-100 fs (even sub-10 fs) pulses in the near infrared and are widely used in many high impact scientific fields. However, the need for a bulky, expensive and complex pump source, typically a frequency-doubled multi-watt neodymium or optically pumped semiconductor laser, represents the main obstacle to more widespread use. The recent development of blue diodes emitting over 1 W has opened up the possibility of directly diode-laser-pumped Ti:sapphire oscillators. Beside the lower cost and footprint, a direct diode pumping provides better reliability, higher efficiency and better pointing stability to name a few. The challenges that it poses are lower absorption of Ti:sapphire at available diode wavelengths and lower brightness compared to typical green pump lasers. For practical applications such as bio-medicine and nano-structuring, output powers in excess of 100 mW and sub-100 fs pulses are required. In this paper, we demonstrate a high average power directly blue-diode-laser-pumped Ti:sapphire oscillator without active cooling. The SESAM modelocking ensures reliable self-starting and robust operation. We will present two configurations emitting 460 mW in 82 fs pulses and 350 mW in 65 fs pulses, both operating at 92 MHz. The maximum obtained pulse energy reaches 5 nJ. A double-sided pumping scheme with two high power blue diode lasers was used for the output power scaling. The cavity design and the experimental results will be discussed in more details.

Laser surface structuring with 100 W of average power and sub-ps pulses

High throughput still represents a key factor for industrial use of ultrashort pulses in the field of surface structuring. Reliable systems with average powers up to 100 W are today available. It has already been proved that metals, especially steel having a low threshold fluence, can be machined with excellent surface quality at average powers of more than 40 W and a spot radius of about 25 μm, if a polygon line scanner, offering fast scanning speeds, is used. A further scale-up into the 100 W regime should be possible for metals showing a threshold fluence of about 0.2 J/cm2 or higher. But, it will lead to problems with heat accumulation in the case of steel and a straight forward scale-up is not possible. In order to keep a good surface quality, the machining strategy has to be adapted. A maximum flexibility can be obtained with an “interlaced” mode by using very high marking speeds of several 100 m/s and repetition rates of several tenths of MHz. As this is at the edge of today available technologies,...

Time- and spectrally resolved ultrafast gain dynamics of a semiconductor optical amplifier under phase-correlated multiwavelength pulse amplification

The ultrafast gain dynamics of an AlGaAs semiconductor optical amplifier (SOA) are measured under phase-correlated multiwavelength pulse amplification using time-resolved pump–probe techniques. Both the temporal and spectral gain dynamics are measured. Carrier heating due to two photon absorption, carrier cooling, four-wave mixing, and cross-phase modulation effects are observed. These effects are evident when amplifying dispersion compensated pulses, and it is shown how these effects decrease when amplifying nondispersion compensated (chirped) pulses. This helps to avoid nonlinear effects in the gain media (SOA), which, in turn, helps to support the operation of external cavity multiwavelength semiconductor mode-locked lasers where the intracavity pulses are inherently chirped.

Experimental characterization and numerical simulations of dispersion-managed breathing-mode semiconductor mode-locked ring laser

Strong self-phase modulation (SPM) in semiconductor gain media induces nonlinear chirp impressed on propagating pulses, which can be difficult to compensate. Our approach is to employ an intracavity dispersion management scheme to decrease the detrimental effect of SPM by utilizing the concept of chirped pulse amplification inside a laser cavity. Stretching the pulse before the cavity gain element minimizes SPM and extracts energy more efficiently. The subsequently compressed pulse bleaches the semiconductor saturable absorber (SA) more easily. The breathing-mode semiconductor mode-locked ring laser regime describes how the pulse alternately experiences stretching and compression while propagating within the ring cavity.

Dynamic fiber delivery of 3 W 160 fs pulses with photonic crystal hollow core fiber patchcord

We report output characteristics from the FC/APC connectorized photonics crystal hollow core fiber when is subjected to coiling down to 50 mm radius, bending, torsion etc. We achieved coupling efficiency up to 75%, output average power 2 W and 24 nJ pulse energy. With proper coupling the depolarization could be as low as 7%. Torsion of the photonic crystal patchcord destroys the polarization and other pulse properties.