Vid Agrež

Gain-switched Yb-doped fiber laser for microprocessing

The gain-switched fiber laser presents the simplest construction among pulsed lasers in the nanosecond region and consequently is also very robust. These properties make it potentially appropriate for industrial applications, especially in some types of microprocessing. However, careful design of such lasers is important in order to reach the required pulse parameters (peak power and pulse duration). To design and optimize a gain-switched fiber laser for microprocessing, a numerical model using time and spatial dependencies was developed and reported in this paper. The effects of pump power and laser length on the pulse duration and peak power were investigated by modeling gain-switched operation. Further, the results of modeling were compared to data from an experimental setup based on a Yb3+-doped gain-switched fiber laser, revealing good agreement.

Single stage Yb-doped fiber laser based on gain switching with short pulse duration

A simple solution for producing nanosecond laser pulses can be obtained using gain-switched fiber lasers. In this paper, we present an optimized single stage gain-switched ytterbium-doped fiber laser. Three fiber lengths were tested to show the impact of length on the laser output pulse. A pulse as short as 28 ns at 1.4 kW peak power and a maximum peak power of nearly 2 kW at 41 ns pulse duration was achieved. The laser possess a linear polarized output, very good beam quality of M2 < 1.1, and a spectral bandwidth of 0.11 nm.

Gain switch laser based on micro-structured Yb-doped active fiber

In this paper a near infrared gain-switched fiber laser based on oscillator stage only design with high peak power is presented. Output pulses reached 2.3 kW of peak power and duration of less than 60 ns. The dependence of the laser pulse duration on operation parameters was measured and theoretically explained. As the setup is based on flexible micro structured single polarization fiber, the laser output exhibits high polarization extinction ratio. Due to the narrow output spectrum the setup is suitable for second harmonic generation.

Effect of repetition rate on gain-switched fiber laser output pulses

We investigate the influence of repetition rate on the operation and output of a gain-switched fiber laser. We derive an equation relating pump pulse duration to repetition rate, which provides insight into the parameters of the operating laser such as absorbed pump power and internal losses. The change in laser pulse duration with varying repetition rate is measured and found to be negligible. Finally, the derived theory is compared to experimental results obtained using a ytterbium-doped rod type fiber laser.

Gain-switching of a fiber laser: experiment and a simple theoretical model

We present a study of a gain-switched end-pumped Yb-doped-fiber laser. The test laser that was mainly used in order to verify the theoretical model consist of an 8.7 m long double clad active fiber with core and inner cladding diameter of 8 μm and 130 μm respectively, and absorption of 1.5 dB/m. An important part of the system is a control unit that switches on the pumping diodes at a desired repetition rate and switches off at the moment when the first spike of the transitional effect appears in order to suppress additional oscillations. A simple rate equation model accurately predicts the main pulse parameters. It describes the population dynamics of the photons and the laser levels, including the occupation by thermal effects. Further numerical simulations show that with adequate active fiber geometry, active ion doping and sufficient pumping power, much shorter pulses in range of 50 ns and peak power of several 100W can be achieved. Such a simple system with the potential addition of a one stage active fiber amplifier can be interesting for some applications in micro-processing like scribing of solar cells, micro processing, and thin film removal.

High power fiber MOPA based QCW laser delivering pulses with arbitrary duration on demand at high modulation bandwidth

We report on a concept of a fiber MOPA based quasi-CW laser working at high modulation bandwidths up to 40 MHz capable of producing arbitrary pulse durations at arbitrary repetition rates. An output power of over 100 W was achieved and an on-off contrast of 25 dB. The laser features a dual-channel (dual-wavelength) seed source, a double stage YDF amplifier and a volume-Bragg-grating-based signal de-multiplexer. Minimization of transients was conducted through experiment and model analysis.

Short pulsed gain-switched fiber laser with improved efficiency utilizing unabsorbed pump recovery.

A simple solution for increasing the slope efficiency of a gain-switched fiber laser based on Yb-doped active fiber is presented. By adding a fiber amplifier stage, which recovers the unabsorbed pump light from the gain-switched oscillator, a significant increase in slope efficiency is achieved. The pulses at 1030-nm wavelength have an FWHM of 28 ns and a peak power of 2.3 kW.

Gain-switched ytterbium-doped rod-type fiber laser

The operation of a gain-switched ytterbium-doped rod-type fiber laser is presented in this paper. The pumping, output pulses, spectrum, and energy stability are analyzed. The two key parameters of the laser pulse achieved from the single-stage gain-switched system are a 43 ns pulse duration and a peak power of 4.4 kW. This is to our knowledge the highest peak power obtained from single stage gain switched Yb-doped fiber laser. Further a very good pulse-to-pulse stability with standard deviation of less than 1% was achieved.

Experimental and theoretical study of gain switched Yb-doped fiber laser

First pulse of relaxation oscillations that appear after the start of the pumping can be used to realize an efficient pulsed laser based on gain switching. Because there is no need for any additional active optical element this can be very simple and robust technique to produce nanosecond pulses. Together with fiber technology it can produce compact and reliable lasers appropriate for industrial applications such as micro-processing. However, to produce pulses with appropriate peak power and duration, one must carefully design such systems. We report on a numerical model that describes time and spatial dependencies of photon and ion populations which was developed to enable design and optimization of a gainswitched fiber laser. The peak pump power influence on basic output laser pulse parameters is presented in this paper. To confirm theoretical result an experimental setup was built around double clad ytterbium doped fiber laser.

Fiber laser for high speed laser transfer printing

High speed industrial laser transfer printing requires high power lasers that can deliver pulses on demand and having arbitrary pulse duration in range of few nanoseconds to milliseconds or more. A special kind of MOPA fiber laser is presented using wavelength multiplexing to achieve pulses on demand with minimal transients. The system is further tested in printing application.