E. Gini

Experimentally confirmed design guidelines for passively Q-switched microchip lasers using semiconductor saturable absorbers

We present a model for passively Q-switched microchip lasers and derive simple equations for the pulse width, repetition rate, and pulse energy. We experimentally verified the validity of the model by systematically varying the relevant device parameters. We used the model to derive practical design guidelines for realizing operation parameters that can be varied in large ranges by adoption of the parameters of the semiconductor saturable-absorber mirror and choice of the appropriate gain medium. Applying these design guidelines, we obtained 37-ps pulses, which to our knowledge are the shortest pulses ever generated in a passively Q-switched solid-state laser.

Quantum-cascade lasers based on a bound-to-continuum transition

Laser emission at about 3.5 THz from quantum cascade lasers based on a bound-to-continuum transition is reported. Maximum pulsed operation temperature is above liquid nitrogen (90 K). CW operation reaches 55 K with powers up to 15 mW at 10 K.

External cavity quantum cascade laser tunable from 7.6 to 11.4 μm

We present the development of a broad gain quantum cascade active region. By appropriate cascade design and using a symmetric active region arrangement, we engineer a flat gain and increase the total modal gain in the desired spectral range. Grating-coupled external cavity quantum cascade lasers using this symmetric active region are tunable from 7.6 to 11.4 μm with a peak optical output power of 1 W and an average output power of 15 mW at room-temperature. With a tuning of over 432 cm−1, this single source covers an emission range of over 39% around the center frequency.

High-power passively mode-locked semiconductor lasers

We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties

Passively Q-switched 0.1mJ fiber laser system at 1.53µm

We demonstrate a passively Q-switched fiber laser system generating pulses with as much as 0.1 mJ pulse energy at 1.53µm and > 1kHz repetition rate. This was achieved with a simple MOPA (master oscillator, power amplifier) scheme with a single pump source, realized with large mode area fiber and multiple reflections on a semiconductor saturable absorber mirror (SESAM).

Broadband tuning of external cavity bound-to-continuum quantum-cascade lasers

A quantum-cascade structure based on a bound-to-continuum design exhibiting a broad gain curve is presented. The full width at half maximum of the measured luminescence spectrum is 297 cm−1 at room temperature. Grating-coupled external cavity lasers using this active region could be tuned over 150 cm−1 (1.45 μm), which is equal to 15% of the free running wavelength (λ≅10 μm), in pulsed mode at room temperature. Time resolved spectra showed a single-mode operation with a 30 dB side mode suppression ratio after the first 12 ns of the pulse.

External cavity quantum-cascade laser tunable from 8.2to10.4μm using a gain element with a heterogeneous cascade

A heterogeneous quantum-cascade structure based on two bound-to-continuum designs emitting at 9.6 and 8.4μm is presented. Its spontaneous emission spectrum at room temperature has a full width at half maximum of 350cm−1 and shows a variation of intensity of less than 20% over more than 200cm−1. External cavity lasers using a grating in Littrow configuration and antireflection coated chips with this active region could be tuned over 265cm−1 from 8.2to10.4μm, that is, over 24% of the center wavelength.

50-GHz passively mode-locked surface-emitting semiconductor laser with 100-mW average output power

We have developed a passively mode-locked optically-pumped vertical-external-cavity surface-emitting semiconductor laser (VECSEL) which delivers up to 100 mW of average output power at a repetition rate of 50 GHz in nearly transform-limited 3.3-ps pulses at a wavelength around 960 nm. The high-repetition-rate passive mode locking was achieved with a low-saturation-fluence semiconductor saturable absorber mirror (SESAM) incorporating a single layer of quantum-dots. The output power within a nearly diffraction-limited beam was maximized using a gain structure with a low thermal impedance soldered to a diamond heat spreader. In addition, we systematically optimized the laser resonator to accommodate for the strong thermal lens caused by the optical pumping. We measured the thermal lens dioptric power and present a numerical model which is in good agreement with the measurements and is useful for optimizing resonator designs. The experimental setup is very versatile and its design and construction are discussed in detail

2.1-W picosecond passively mode-locked external-cavity semiconductor laser

We demonstrate an optically pumped passively mode-locked external-cavity semiconductor laser generating 4.7-ps pulses at 957 nm with as much as 2.1 W of average output power and a 4-GHz repetition rate. Compared with earlier results, the chirp of the pulses has been greatly reduced by use of an intracavity etalon. Apart from restricting the bandwidth, the etalon also helps optimize wavelength-dependent gain parameters and dispersion.

Highly efficient optically pumped vertical-emitting semiconductor laser with more than 20 W average output power in a fundamental transverse mode

We have demonstrated an optically pumped vertical-external-cavity surface-emitting laser (OP-VECSEL) generating more than 20 W of cw output power in a fundamental transverse mode (M2 approximately 1.1) at 960 nm. The laser is highly efficient with a slope efficiency of 49%, a pump threshold of 4.4 W, and an overall optical-to-optical efficiency of 43%.