Florian Mörz

Multi-Watt femtosecond optical parametric master oscillator power amplifier at 43 MHz.

We present a high repetition rate mid-infrared optical parametric master oscillator power amplifier (MOPA) scheme, which is tunable from 1370 to 4120nm. Up to 4.3W average output power are generated at 1370nm, corresponding to a photon conversion efficiency of 78%. Bandwidths of 6 to 12nm with pulse durations between 250 and 400fs have been measured. Strong conversion saturation over the whole signal range is observed, resulting in excellent power stability. The system consists of a fiber-feedback optical parametric oscillator that seeds an optical parametric power amplifier. Both systems are pumped by the same Yb:KGW femtosecond oscillator.

Ultra-stable high average power femtosecond laser system tunable from 1.33 to 20 μm.

A highly stable 350 fs laser system with a gap-free tunability from 1.33 to 2.0 μm and 2.13 to 20 μm is demonstrated. Nanojoule-level pulse energy is achieved in the mid-infrared at a 43 MHz repetition rate. The system utilizes a post-amplified fiber-feedback optical parametric oscillator followed by difference frequency generation between the signal and idler. No locking or synchronization electronics are required to achieve outstanding free-running output power and spectral stability of the whole system. Ultra-low intensity noise, close to the pump lasers noise figure, enables shot-noise limited measurements.

High repetition rate mid-infrared supercontinuum generation from 1.3 to 5.3 μm in robust step-index tellurite fibers

We demonstrate broadband supercontinuum generation over two infrared octaves, spanning from 1.3 to 5.3 μm, with an output power of 150 mW in robust step-index tellurite fibers with core diameters between 3.5 and 4.3 μm. As a pump source, we use femtosecond mid-IR pulses from a home-built post-amplified optical parametric oscillator tunable between 1.5 and 4.0 μm at a 43 MHz repetition rate. We study the influence of core size, pump wavelength, and fiber length to optimize the spectral bandwidth. A key requirement for efficient spectral broadening is a low and rather flat average anomalous dispersion over a wide spectral range that can be tailored accordingly by changing the fiber core diameter. Numerical simulations based on the generalized nonlinear Schrodinger equation are in good agreement with experimental results.

Solitonic supercontinuum of femtosecond mid-IR pulses in W-type index tellurite fibers with two zero dispersion wavelengths

We present a detailed experimental parameter study on mid-IR supercontinuum generation in W-type index tellurite fibers, which reveals how the core diameter, pump wavelength, fiber length, and pump power dramatically influence the spectral broadening. As pump source, we use femtosecond mid-IR pulses from a post-amplified optical parametric oscillator tunable between 1.7 μm and 4.1 μm at 43 MHz repetition rate. We are able to generate red-shifted dispersive waves up to a wavelength of 5.1 μm by pumping a tellurite fiber in the anomalous dispersion regime between its two zero dispersion wavelengths. Distinctive soliton dynamics can be identified as the main broadening mechanism resulting in a maximum spectral width of over 2000 nm with output powers of up to 160 mW. We experimentally demonstrated that efficient spectral broadening with considerably improved power proportion in the important first atmospheric transmission window between 3 and 5 μm can be achieved in robust W-type tellurite fibers pumped at long wavelengths by ultra-fast lasers.

Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 133 to 8 µm

Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 µm (10 000 – 500 cm−1) in FTIR spectrometers. However, measuring sample areas below 40x40 µm2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 – 7520 cm−1 (1.33 – 8 µm). We demonstrate mapping of a 150x150 µm2 sample of 100 nm thick molecule layers at 1430 cm−1 (7 µm) with 10x10 µm2 spatial resolution and a scan speed of 3.5 µm/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance.

Nanoscale Hydrogenography on Single Magnesium Nanoparticles

Active plasmonics is enabling novel devices such as switchable metasurfaces for active beam steering or dynamic holography. Magnesium with its particle plasmon resonances in the visible spectral range is an ideal material for this technology. Upon hydrogenation, metallic magnesium switches reversibly into dielectric magnesium hydride (MgH2), turning the plasmonic resonances off and on. However, up until now, it has been unknown how exactly the hydrogenation process progresses in the individual plasmonic nanoparticles. Here, we introduce a new method, namely nanoscale hydrogenography, that combines near-field scattering microscopy, atomic force microscopy, and single-particle far-field spectroscopy to visualize the hydrogen absorption process in single Mg nanodisks. Using this method, we reveal that hydrogen progresses along individual single-crystalline nanocrystallites within the nanostructure. We are able to monitor the spatially resolved forward and backward switching of the phase transitions of several individual nanoparticles, demonstrating differences and similarities of that process. Our method lays the foundations for gaining a better understanding of hydrogen diffusion in metal nanoparticles and for improving future active nano-optical switching devices.

Monitoring protein configurations in the fingerprint region with micro-FTIR spectroscopy by employing a 98 fs solid-state laser tunable from 1.33 to 8 µm at 73 MHz repetition rate (Conference Presentation)

We monitor the configuration of poly-L-lysine proteins using vibrational resonances at 6 µm (1667 cm^-1) by employing a broadband femtosecond solid-state laser for micro-FTIR spectroscopy. This laser system allows for detection of minute amounts of proteins due to a several orders of magnitude higher brilliance compared to standard FTIR light sources such as globars. Thus, absorption signals as small as 0.5% can be detected without averaging, compared to 6.4% using a globar, at a spatial resolution as small as 10x10 µm^2. Our light source is based on a 98 fs, Yb-doped pump laser at 73 MHz repetition rate, providing 2.5 W average power. By pumping a fiber-feedback optical parametric oscillator (ffOPO) and a post-amplifier, signal and idler beams spanning from 1.33 – 2.0 and 2.1 – 4.6 µm are generated. The tuning range is extended to 8 µm by difference frequency generation between the signal and idler beams and can be further extended by using a pump laser with higher output power. At 7 µm excellent long-term wavelength stability with fluctuations smaller than 0.1% rms measured over 9 hours is observed, without applying electronic stabilization. This is due to the combination of a ffOPO with a post-amplifier and is distinctly superior over other systems based on free-space OPOs. Protein sensing is conducted by applying resonant surface-enhanced infrared absorption (SEIRA) spectroscopy, using a single gold nanoantenna. To the best of our knowledge, this is the first demonstration of resonant SEIRA spectroscopy using a single nanoantenna with a laser system as light source.

High-power mid-infrared high repetition-rate supercontinuum source based on a chalcogenide step-index fiber

We demonstrate a tunable and robust femtosecond supercontinuum source with a maximum output power of 550 mW and a maximum spectral width of up to 2.0 μm which can cover the mid-infrared region from 2.3 μm up to 4.9 μm by tuning the pump wavelength. As light source we use a synchronously pumped fiber-feedback OPO and a subsequent OPA which delivers femtosecond, Watt level idler pulses tunable between 2.5 μm and 4.1 μm. These pulses are launched into As2S3 chalcogenide step-index fibers with core diameters of 7 and 9 μm. The spectral behavior of the supercontinuum is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. Self-phase modulation is identified as the main broadening mechanism in the normal dispersion regime. This source promises to be an excellent laboratory tool for infrared spectroscopy owing to its high brilliance as demonstrated for the CS2- absorption bands around 3.5 μm.

Solitonic supercontinuum of fs mid-IR pulses in W-type index tellurite fibers with two zero dispersion wavelengths

We are able to generate red-shifted dispersive waves up to a wavelength of 5.1 µm by pumping a W-type index tellurite fiber in the anomalous dispersion regime between its two zero dispersion wavelengths.