Difference frequency generation setups suffer from beam pointing offsets during wavelength tuning due to angular phase-matching. We present a stable scheme that circumvents crystal rotation and achieves a 10 times efficiency improvement for λ>11 µm.

Tunable mid-infrared ultrashort lasers have become an essential tool in vibrational spectroscopy in recent years. They enabled and pushed a variety of spectroscopic applications due to their high brilliance, beam quality, low noise, and accessible wavelength range up to 20 µm. Many state-of-the-art devices apply difference frequency generation (DFG) to reach the mid-infrared spectral region. Here, birefringent phase-matching is typically employed, resulting in a significant crystal rotation during wavelength tuning. This causes a beam offset, which needs to be compensated to maintain stable beam pointing. This is crucial for any application. In this work, we present a DFG concept, which avoids crystal rotation and eliminates beam pointing variations over a broad wavelength range. It is based on two independently tunable input beams, provided by synchronously pumped parametric seeding units. We compare our concept to the more common DFG approach of mixing the signal and idler beams from a single optical parametric amplifier (OPA) or oscillator (OPO). In comparison, our concept enhances the photon efficiency of wavelengths exceeding 11 µm more than a factor of 10 and we still achieve milliwatts of output power up to 20 µm. This concept enhances DFG setups for beam-pointing-sensitive spectroscopic applications and can enable research at the border between the mid- and far-IR range due to its highly efficient performance.

We present a broadly tunable highly efficient frequency conversion scheme, based on a low-threshold harmonic cavity optical parametric oscillator (OPO) followed by an idler-seeded power amplifier. By choosing the cavity length of the OPO equal to the 10th harmonic of its 41 MHz Yb:KGW solid-state pump laser, a very compact optical setup is achieved. A singly-resonant cavity without output coupler results in a low oscillation threshold of only 28-100 mW in the entire signal tuning range of 1.37-1.8 µm. The 2.4-4.15 µm idler radiation is coupled out at the 41 MHz pump frequency and employed to seed a post amplifier with nearly Watt-level output power. In addition, the seeder plus power amplifier concept results in clean signal and idler pulses at the fundamental repetition rate of 41 MHz with a time-bandwidth product below 0.4 and a relative intensity noise 10 dB lower compared to the solid-state pump laser.

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.

We demonstrate broadband supercontinuum generation over two infrared octaves, spanning from 1.3 to 5.3 mu m, with an output power of 150 mW in robust step-index tellurite fibers with core diameters between 3.5 and 4.3 mu m. 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 mu m 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. (C) 2017 Optical Society of America

We present mid-infrared supercontinuum sources based on chalcogenide, tellurite, and liquid-filled capillary fibers and sub-picosecond oscillator pumping. Depending on the fiber geometry and material, the experimentally achieved spectral bandwidths and output powers vary significantly. In As2S3 chalcogenide step-index fibers we achieve a maximum output power of 550 mW at a spectral width of 2 μm, covering the important transparent atmospheric window between 3 and 5 μm. In tellurite step-index fibers we attain an ultra-broadband spectrum ranging from 1.3 to 5.3 μm with an average power of 150 mW. The spectral behavior of the supercontinua is investigated by changing the pump wavelength, core diameter, fiber length, and pump power. As pump source we use high repetition rate (42 MHz) optical parametric oscillators/amplifiers which deliver Watt-level pulses tunable between 1.4 – 4.1 μm. These supercontinuum sources promise to be excellent laboratory tools for high resolution spectroscopy owing to their high brilliance and near TEM00 spatial beam profiles.

Optical system and method for the provision of at least one high-frequency modulated light pulse having a pump light source for the provision of high-frequency pump light pulses; an optical resonator having a coupling element for coupling the pump light pulses into the resonator and a decoupling element for decoupling the at least one high-frequency modulated light pulse from the resonator and an optically non-linear frequency conversion medium arranged in the resonator for transforming the pump light pulses in each case into two conversion light pulses and one residual pump light pulse. The resonator comprises a feedback arm for at least one of the two conversion light pulses and/or the residual pump light pulse, in which an optically non-linear feedback medium is arranged for the optical modulation of the at least one conversion light pulse and/or the residual pump light pulse.

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 mu m (10 000 - 500 cm(-1)) in FTIR spectrometers. However, measuring sample areas below 40x40 mu m(2) 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 mu m). We demonstrate mapping of a 150x150 mu m(2) sample of 100 nm thick molecule layers at 1430 cm(-1) (7 mu m) with 10x10 mu m(2) spatial resolution and a scan speed of 3.5 mu m/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. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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 Schrödinger equation are in good agreement with experimental results.

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.

A system (1; 2; 3) for coherent Raman spectroscopy, comprises a first optical parametric amplifier (30) providing a first light pulse (100), a pulsed laser (20) providing a second light pulse (200) such that a first fraction (201) of the second light pulse (200) pumps the first optical parametric amplifier (30), and a cw-laser (10) seeding the first optical parametric amplifier (30). Therein, the first light pulse (100) and a second fraction (202) of the second light pulse (200) are converted into a synchronised pump pulse (103) and Stokes pulse (203) for coherent Raman spectroscopy with a predetermined tunable frequency difference between the pump pulse (103) and the Stokes pulse (203).

We demonstrate that period doubling in a synchronously-pumped OPO is a powerful alternative to acousto- or electro-optical modulators for pump-probe spectroscopy. High-speed SRS microscopy with all-optical modulation is presented for the first time.

Die vorliegende Erfindung betrifft ein Verfahren zum Verbinden einer optischen Festkernfaser (2) mit einer weiteren optischen Faser (20), wobei die optische Festkernfaser (2) eine Fugungsvorrichtung (10) aufweist, welche an einem axialen Ende der optischen Festkernfaser (2) mit Hilfe eines 3D-Druckers ausgebildet wird und wobei die weitere optischen Faser (20) durch Einfuhren eines axialen Endes der weiteren optischen Faser (20) in die Fugungsvorrichtung (10) mit der optischen Festkernfaser (2) verbunden wird. Zudem betrifft die Erfindung eine optische Festkernfaser (2) mit einer mittels eines 3D-Druckers ausgebildeten Fugungsvorrichtung (10), sowie eine diesbezugliche Verwendung eines 3D-Druckers.

We present powerful alternatives to the “classical” optical parametric oscillator for frequency conversion of ultrafast pulses at high repetition rate. Applications of these sources to stimulated Raman scattering microscopy and high-brilliance Fourier-transform infrared spectroscopy are demonstrated.

We introduce a broadly tunable robust source for fingerprint (170 - 1620 cm-1) Raman spectroscopy. A cw thulium-doped fiber laser seeds an optical parametric amplifier, which is pumped by a 7-W, 450-fs Yb:KGW bulk mode-locked oscillator with 41 MHz repetition rate. The output radiation is frequency doubled in a MgO:PPLN crystal and generates 0.7 - 1.3-ps-long narrowband pump pulses that are tunable between 885 and 1015 nm with >80 mW average power. The Stokes beam is delivered by a part of the oscillator output, which is sent through an etalon to create pulses with 1.7 ps duration. We demonstrate a stimulated Raman gain measurement of toluene in the fingerprint spectral range. The cw seeding intrinsically ensures low spectral drift.

We introduce an extremely simple and highly stable system for stimulated Raman scattering (SRS) microscopy. An 8-W, 450-fs Yb:KGW bulk oscillator with 41 MHz repetition rate pumps an optical parametric amplifier, which is seeded by a cw tunable external cavity diode laser. The output radiation is frequency doubled in a long PPLN crystal and generates 1.5-ps long narrowband pump pulses that are tunable between 760 and 820 nm with >50 mW average power. Part of the oscillator output is sent through an etalon and creates Stokes pulses with 100 mW average power and 1.7 ps duration. We demonstrate SRS microscopy at a 30-μs pixel dwell time with high chemical contrast, signal-to-noise ratio in excess of 45 and no need for balanced detection, thanks to the favorable noise properties of the bulk solid-state system. Cw seeding intrinsically ensures low spectral drift. We discuss its application to chemical contrast microscopy of freshly prepared plant tissue sections at different vibrational bands.

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 laser's noise figure, enables shot-noise limited measurements.

The evolution of supercontinuum generation in chalcogenide suspended-core microstructured optical fibers is studied with regard to their exposure to the room atmosphere. We report the experimental proof of aging-induced supercontinuum generation drift in chalcogenide microstructured fibers. Mid-infrared supercontinuum covering the 2.5–5.5-µm spectral region is demonstrated in a fresh and 7-month-aged counterpart As2S3 fibers, by means of a home-built multistage oscillator power amplifier delivering 300 fs pulses at a repetition rate of 43 MHz in the 3.0–4.1-µm range. Numerical simulations based on the generalized nonlinear Schrödinger equation confirm the significant alteration of supercontinuum generation due to increasing fundamental OH and SH absorption bands.