Sven Schwertfeger

600 mW optical output power at 488 nm by use of a high-power hybrid laser diode system and a periodically poled MgO:LiNbO3 bulk crystal

600 mW second-harmonic blue light at 488 nm has been generated by use of a master-oscillator power amplifier diode laser system as a pump source with a maximum optical output power of 4 W in continuous-wave operation. For frequency doubling, a periodically poled MgO:LiNbO3 bulk crystal was used in a single-pass configuration. A conversion efficiency of 15% and an overall wall-plug efficiency of 4% were achieved.

Nearly-diffraction limited 980 nm tapered diode lasers with an output power of 6.7 W

High-power tapered diode lasers emitting at 980 nm with electrically separated straight and tapered sections have been fabricated. A high beam quality at an output power of 6.7 W was achieved.

High peak power optical pulses generated with a monolithic master-oscillator power amplifier

We present results on a monolithic semiconductor-based master-oscillator power amplifier (MOPA) combining a distributed-feedback (DFB) laser and a tapered amplifier on a single chip. The MOPA reaches an output power of almost 12 W at an emission wavelength around 1064 nm in continuous-wave operation. Pulses with a length of around 100 ps can be obtained either by injecting nanosecond current pulses into the tapered amplifier alone or into both the DFB laser and the tapered amplifier. In the latter case, pulses with a width of 84 ps, a peak power of 42 W, and a spectral width of 160 pm are generated.

Ultra-narrow linewidth DFB-laser with optical feedback from a monolithic confocal Fabry-Perot cavity.

We present a compact, ultra-narrow-linewidth semiconductor laser based on a 780 nm distributed feedback diode laser optically self-locked to a mode of an external monolithic confocal Fabry-Perot resonator. We characterize spectral properties of the laser by measuring its frequency noise power spectral density. The white frequency noise levels at 5 Hz(2)/Hz above a Fourier frequency as small as 20 kHz. This noise level is more than five orders of magnitude smaller than the noise level of the same solitary diode laser without resonant optical feedback, and it is three orders of magnitude smaller than the noise level of a narrow linewidth, grating-based, extended-cavity diode laser. The corresponding Lorentzian linewidth of the laser with resonant optical feedback is 15.7 Hz at an output power exceeding 50 mW.

Picosecond Spectral Dynamics of Gain-Switched DFB Lasers

We study the generation of picosecond pulses by gain-switching of distributed feedback ridge-waveguide laser diodes. By pumping with short current pulses without d.c. bias, we obtain laser pulses with peak powers above 1 W at a wavelength around 1065 nm. These pulses exhibit strong spectral dynamics stemming from mode competition after switch-on. Typically, emission begins with a broad spectrum, before narrowing down to the Bragg line within a few hundred picoseconds. This dynamic behavior is studied in detail both experimentally and numerically for a variety of grating parameters. Using a rate-equation model with two species of photons, we achieve excellent agreement between simulation and experiment. In conclusion, we discuss the optimization of DFB laser diodes for short pulse generation.

Laser driver switching 20 A with 2 ns pulse width using GaN

A GaN-HEMT-based circuit is presented capable of switching 20 A of current with less than about 0.5 ns rise and fall time. This demonstrates the potential of GaN transistors for high-current switching applications, even if breakdown voltage requirements are low. The current driver is used to realize an optical pulse picker generating 10 ps optical pulses of more than 30 W with a variable repetition rate between 1 kHz and 100 MHz.

Dynamics of a gain-switched distributed feedback ridge waveguide laser in nanoseconds time scale under very high current injection conditions

We present detailed experimental investigations of the temporal, spectral and spatial behavior of a gain-switched distributed feedback (DFB) laser emitting at a wavelength of 1064 nm. Gain-switching is achieved by injecting nearly rectangular shaped current pulses having a length of 50 ns and a very high amplitude up to 2.5 A. The repetition frequency is 200 kHz. The laser has a ridge waveguide (RW) for lateral waveguiding with a ridge width of 3 µm and a cavity length of 1.5 mm. Time resolved investigations show, depending on the amplitude of the current pulses, that the optical power exhibits different types of oscillatory behavior during the pulses, accompanied by changes in the lateral near field intensity profiles and optical spectra. Three different types of instabilities can be distinguished: mode beating with frequencies between 25 GHz and 30 GHz, switching between different lateral intensity profiles with a frequency of 0.4 GHz and self-sustained oscillations with a frequency of 4 GHz. The investigations are of great relevance for the utilization of gain-switched DFB-RW lasers as seed lasers for fiber laser systems and in other applications, which require a high optical power.

5.3 W cw output power from a master oscillator power amplifier at 1083nm

A master-oscillator power-amplifier system at λ=1083 nm with 5.3 Watt output power and a narrow spectral linewidth was realised. The master oscillator was a distributed Bragg reflector (DBR) laser with a 3-μm wide ridge waveguide (RW) and a total length of 2 mm. The power amplifiers were a 4 mm long antireflection coated tapered laser diodes with 500 μm or 1000 μm long straight RW sections. At a temperature of 40oC and an injection current of 160 mA, the DBR laser had a wavelength of 1083 nm. The emitted light of the DBR laser was focused into the tapered amplifier with a seed power of up to 36 mW. At 10oC and at a current through the tapered amplifier of 8.6 A, a maximum output power of 5.3 W was measured. Over the full operating range single longitudinal mode operation at a wavelength of λ=1083 nm was maintained with a side mode suppression ratio better than 35 dB. The vertical far field angle was below 22o (FWHM).

600 mW optical output power at 488 nm using a high power hybrid laser diode system and a PPMgLN bulk crystal

Frequency conversion of near infrared diode lasers provides an efficient method to generate laser radiation in the visible spectral range. There are several requirements for efficient frequency doubling like singlemode emission and good beamquality, which can be fulfilled by light sources based on master oscillator power amplifier (MOPA). This contribution reports on the generation of 600 mW output power at 488 nm by single pass frequency doubling. An InGaAs distributed feedback (DFB) laser was used as MO and an InGaAs tapered amplifier as PA in a MOPA diode laser system. A maximum output power of 4 W at 976 nm was achieved in continuous wave operation mode, at a heatsink temperature of about 0°C with this pump source. For frequency conversion a 30 mm long PPMgLN bulk crystal held at 65°C, was used in a simple single-pass configuration. A maximum conversion efficiency of 15% and an overall wall-plug efficiency of 4% were achieved.

Picosecond pulses with more than 60 W peak power generated by a singlestage all-semiconductor master-oscillator power-amplifier system

Picosecond laser pulses have found widespread applications in numerous fields. While each application has specific requirements concerning power level and wavelength, many of them benefit from variable pulse repetition rates. For example, in material processing, pulse bursts allow for superior cut edges, while in fluorescence spectroscopy, adjustable repetition rates help to avoid photo bleaching.