Andreas Rohrbacher

Green-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power.

We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing.

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.

160 W 800 fs Yb:YAG single crystal fiber amplifier without CPA.

We demonstrate a compact and simple two-stage Yb:YAG single crystal fiber amplifier which delivers 160 W average power, 800 fs pulses without chirped pulse amplification. This is the highest average power of femtosecond laser based on SCF. Additionally, we demonstrate the highest small signal gain of 32.5 dB from the SCF in the first stage and the highest extraction efficiency of 42% in the second stage. The excellent performance of the second stage was obtained using the bidirectional pumping scheme, which is applied to SCF for the first time.

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.

Low cost laser system generating 26-fs pulse duration, 30-kW peak power, and tunability from 800 to 1200 nm for multiphoton microscopy

We demonstrate a novel low-cost, low-noise, tunable, high-peak-power, ultrafast laser system based on a SESAMmodelocked, solid-state Yb tungstate laser plus spectral broadening via a microstructured fiber followed by pulse compression. The spectral selection, tuning, and pulse compression are performed with a simple prism compressor. The spectral broadening and fiber parameters are chosen to insure low-noise and short pulse operation of the tunable output. The long-term stable output pulses are tunable from 800 to 1200 nm, with a peak power up to 30 kW and pulse duration down to 26 fs. We demonstrate the generation of an output beam with 30 fs pulsewidth and multiple colors in infrared. In particular, we compressed selected spectral slices centered at 960 and 1100 nm suitable for imaging with green fluorescent protein and red dyes. Such a multicolor, 30 fs laser is ideally suited for simultaneous multispectral multiphoton imaging. This system is attractive for variety of applications including multiphoton (TPE, SHG, THG, CARS) and multimodal microscopy, nanosurgery, and optical coherence tomography (OCT). Such system is simpler, lower-cost, and much easier to use (fully turn-key) compared to a currently available solutions for near-infrared ultrashort pulses, typically a Ti:sapphire laser-pumped OPO.

Multiphoton imaging with blue-diode-pumped SESAM-modelocked Ti:sapphire oscillator generating 5 nJ 82 fs pulses

Multicolor two-photon fluorescence imaging is performed using blue-diode-pumped SESAM-modelocked Ti:Sapphire oscillator generating 5 nJ pulse energy, 82 fs pulse duration, at 780 nm central wavelength, with 92 MHz pulse repetition rate.

100W class compact Yb:YAG single crystal fiber amplifier for femtosecond lasers without CPA

Single crystal fibers (SCF) represent an alternative technology for ultrashort pulse amplification to high average power in a simple architecture. SCF have an aspect ratio of a short rod fiber or a thin and long crystal and benefit several advantages from the both concepts. Relatively short interaction length and large signal beam diameter mitigate the nonlinear effects and allow direct amplification of femtosecond pulses avoiding the standard chirped pulse amplification (CPA) technique. In this paper, we demonstrate the amplification of femtosecond pulses up to 160 W of average power using a compact and simple two-stage SCF amplifier without CPA. High brightness pumping and a double-pass signal configuration of the first stage allowed us to reach the small signal gain value of 32.5 dB, i.e. almost 2000, which is the highest reported value. Additionally, we implemented for the first time the bidirectional pumping scheme in the second stage. With the total pump power of 300 W, we achieved the highest average power of femtosecond pulses and the highest extraction efficiency from the SCF, i.e. 160 W and 42 %, respectively. The pulse duration at the maximum output power was measured to be 800 fs assuming sech2 temporal shape. The amplification details and spectral, temporal and spatial characterization of the output beam will be presented.

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.

Low noise laser system generating 26 fs pulse duration, 30 kW peak power, and tunability from 800 to 1200 nm for ultrafast spectroscopy and multiphoton microscopy

We demonstrate a novel low noise, tunable, high-peak-power, ultrafast laser system based on a SESAM-modelocked, solid-state Yb tungstate laser plus spectral broadening via a microstructured fiber followed by pulse compression. The spectral selection, tuning, and pulse compression are performed with a simple prism compressor. The spectral broadening and fiber parameters are chosen to insure low-noise operation of the tunable output. The long-term stable output pulses are tunable from 800 to 1200 nm, with a peak power up to 30 kW and pulse duration down to 26 fs. This system is attractive for variety of applications including ultrafast spectroscopy, multiphoton (TPE, SHG, THG, CARS) and multimodal microscopy, nanosurgery, nanostructuring, and optical coherence tomography (OCT). Such system is simpler, lower-cost, and much easier to use (fully turn-key) compared to a currently available solutions for near-infrared ultrashort pulses, typically a Ti:sapphire laser-pumped OPO.