Generation Of Mid-infrared Pulses Research Articles

Tunable mid-infrared (6.3-12 μm)optical vortex pulse generation.

We demonstrated widely tunable mid-infrared (6.3-12 μm) optical vortex pulse generation from a ZGP difference frequency generator pumped by a 2 μm optical vortex laser with a cascaded KTP geometry. The mid-infrared vortex output carried the same topological charge as that of the 1 μm pump output without any destruction. A pulse energy of >135 μJ was obtained in the wavelength region of 6.3-7.0 μm.

Mid-infrared pulse generation via achromatic quasi-phase-matched OPCPA.

We demonstrate a new regime for mid-infrared optical parametric chirped- pulse amplification (OPCPA) based on achromatic quasi-phase-matching. Our mid-infrared OPCPA system is based on collinear aperiodically poled lithium niobate (APPLN) pre-amplifiers and a non-collinear PPLN power amplifier which is operated in an achromatic phase-matching configuration. The idler output has a bandwidth of 800 nm centered at 3.4 µm. After compression, we obtain a pulse duration of 44.2 fs and a pulse energy of 21.8 µJ at a repetition rate of 50 kHz. We explain the wide applicability of the non-collinear QPM amplification scheme we used, including how it could enable octave-spanning OPCPA in a single device when combined with an aperiodic QPM grating.

Graphene Q-switched 278 μm Er^3+-doped fluoride fiber laser

We report a diode-pumped 2.78 μm Er3+-doped ZBLAN fiber laser passively Q switched by a graphene saturable absorber, which was directly deposited onto a fiber dichroic mirror by the method of optically driven deposition. Stable Q-switched operation with a pulse duration of 2.9 μs and a pulse energy of 1.67 μJ was achieved in a 10 m long gain fiber. The pulse duration was reduced to 1 μs when the gain fiber length was shortened to 2 m. This Letter demonstrates that graphene is a promising and reliable saturable absorber for mid-infrared pulse generation at 3 μm.

Milliwatt-level frequency combs in the 8–14 μm range via difference frequency generation from an Er:fiber oscillator

We report on the generation of mid-infrared (mid-IR) pulses with a maximum average optical power of 4 mW and wide tunability in the 8-14 μm range via difference frequency generation (DFG) in GaSe from an Er:fiber laser oscillator. The DFG process is seeded with self-frequency shifted Raman solitons that are shown to be phase coherent within the whole tuning range, from 1.76 to 1.93 μm. Interference measurements between adjacent pulses at the idler wavelengths attest coherence transfer to the mid-IR.

Generation of Phase-Stable Sub-Cycle Mid-Infrared Pulses from Filamentation in Nitrogen

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a laser-induced filament. The fundamental (ω1) and second harmonic (ω2) output of a 30-fs Ti:sapphire amplifier were focused into nitrogen gas and produce phase-stable broadband MIR pulses (ω0) by using a four-wave mixing process (ω1 + ω1 - ω2 → ω0) through filamentation. The spectrum spread from 400 cm-1 to 5500 cm-1, which completely covered the MIR region. The low frequency components were detected by using an electro-optic sampling technique with a gaseous medium. The efficiency of the MIR pulse generation was very sensitive to the delay between the fundamental and second harmonic pulses. It was revealed that the delay dependence of the efficiency came from the interference between two opposite parametric processes, ω1 + ω1 - ω2 → ω0 and ω2 - ω1 - ω1 → ω0. The pulse duration was measured as 6.9 fs with cross-correlation frequency-resolved optical gating by using four-wave mixing in nitrogen. The carrier-envelope phase of the MIR pulse was passively stabilized. The instability was estimated as 154 mrad rms in 2.5 h.

Generation of phase-stable half-cycle mid-infrared pulses through filamentation in gases

Phase-stable half-cycle mid-infrared pulses were produced through filamentation in argon. The pulse width was obtained as 7.9 fs at 4.1 μm carrier wave length by using frequency-resolved optical gating.

Broadband and tunable mid-infrared laser source based on a transversal array of chirped filaments

A scheme for the generation of broadband and tunable mid-infrared pulses based on two-color filamentation in air is presented. The mid-infrared pulses, spanning the spectral region between 4 and 6.5 μm, result from a third-order nonlinear interaction between two short pulses, one at 800 nm and the other at 437 nm. The latter was created by frequency doubling a Raman-shifted pulse at 873 nm amplified in a chirped-pulse Raman amplifier. Tunability of this mid-infrared laser source was provided by introducing spatial chirp across the fundamental pulse profile which created a transversal array of chirped filaments.

Generation of single-cycle mid-infrared pulses via coherent synthesis

A new approach for the generation of single-cycle mid-infrared pulses without complicated control systems is proposed, which is based on direct coherent synthesis of two idlers generated by difference frequency generation (DFG) processes. It is found that the waveform of synthesized pulses is mainly determined by the spectra superposition, the carrier-envelope phase (CEP) difference, the relative timing and the chirp ratio between the idlers. The influences of these parameters on the synthesized waveform are also numerically calculated and analyzed via second-order autocorrelation, which offers general guidelines for the waveform optimization. The single-cycle synthesized mid-infrared pulses, which are centered at 4233 nm with the spectrum spanning from 3000 nm to 7000 nm, are achieved by carefully optimizing these parameters. The single-cycle mid-infrared laser source presents the possibility of investigating and controlling the strong field light-matter interaction.

Difference frequency generation of femtosecond mid infrared pulses employing intense Stokes pulses excitation in a photonic crystal fiber

We demonstrate a novel method of generating milli-watt level mid-IR (MIR) pulses based on difference frequency mixing of the output from a 40 MHz Yb fiber Chirped Pulse Amplifier (CPA) and the intense Stokes pulses generated in a photonic crystal fiber (PCF) with two closely spaced zero dispersion wavelengths (ZDW). By taking advantage of the unique dispersion profile of the fiber, high power narrowband Stokes pulses are selectively generated in the normal dispersion region of the PCF with up to 1.45 nJ of pulse energy. Mixing with 12 nJ of pump pulses at 1035 nm in a type-II AgGaS(2) crystal yields MIR pulses around 5.5 µm wavelength with up to 3 mW of average power and 75 pJ of pulse energy. The reported method can be extended to generation of other MIR wavelengths by selecting PCFs with different second ZDWs or engineering the fiber dispersion profile via longitudinal tapering.

Generation of tunable octave-spanning mid-infrared pulses by filamentation in gas media

The continued development of femtosecond mid-infrared (IR) sources with ultrabroad spectral width is critical for probing and controlling complex molecular structural dynamics on an ultrafast timescale. We report on a sub-20 fs, coherent mid-IR source with an octave-spanning spectral bandwidth (>2000 cm(-1)) tunable from 2-8 micrometers (37.5-150 THz), with energy >0.4 μJ/pulse at 1 kHz. The mid-IR pulses are generated by four-wave mixing during the filamentation of intense 800 nm and 400 nm pulses in various gas media. Spectral tunability is achieved by the choice of gas, pressure and input 800 nm pulse energy.

Generation of intense ultrashort midinfrared pulses by laser-plasma interaction in the bubble regime

As an intense laser pulse propagates through an underdense plasma, the strong ponderomotive force pushes away the electrons and produces a trailing plasma bubble. In the meantime the pulse itself undergoes extreme nonlinear evolution that results in strong spectral broadening toward the long-wavelength side. By experiment we demonstrate that this process can be utilized to generate ultrashort midinfrared pulses with an energy three orders of magnitude larger than that produced by crystal-based nonlinear optics. The infrared pulse is encapsulated in the bubble before exiting the plasma, hence is not absorbed by the plasma. The process is analyzed experimentally with laser-plasma tomographic measurements and numerically with three-dimensional particle-in-cell simulation. Good agreement is found between theoretical estimation, numerical simulation, and experimental results.

Generation of Sub 50-fs Mid-Infrared Pulses by Optical Parametric Amplifier Based on Periodically-Poled MgO:LiNbO3

Femtosecond pulses with the bandwidth in excess of 600 nm in 3–4 µm spectral range were generated by an optical parametric amplifier based on periodically-poled MgO:LiNbO3. We utilized broadband quasi-phase-matching condition, which appears around the idler wavelength of 3400 nm when pumped at 800 nm. The generated mid-infrared pulses were characterized by the frequency-resolved optical gating method in the second-harmonic generation geometry. After the second-order spectral phase was compensated by dispersive transmission through a silicon window, the pulse duration was about 45 fs, corresponding to four optical cycles. Compensation of higher-order spectral phase could enable the generation of few-cycle pulses.

Generation of narrowband subpicosecond mid-infrared pulses via difference frequency mixing of chirped near-infrared pulses

The widely used setup for the generation of femtosecond infrared (IR) pulses based on parametric amplifiers (OPAs) and difference frequency mixing (DFM) is extended to produce tunable narrowband mid-IR pulses. The insertion of pairs of silicon prisms after the OPA induces adjustable chirp, which leads to the generation of narrowband pulses in the DFM stage. Rapid tunability of the mid-IR wavelength via a computer-controllable actuator can be achieved in a range of approximately 200 cm(-1) at a bandwidth of the IR-pulses between approximately 15 and approximately 50 cm(-1) and pulse energies up to 0.4 microJ. The narrowband mid-IR pulses are well suited for 2D IR spectroscopy.

Generation of Broadband Mid-Infrared Pulses by Noncollinear Difference Frequency Mixing

The generation of broadband mid-infrared (MIR) laser pulses by difference frequency mixing (DFM) is investigated. Two-color femtosecond pulses from a Ti:sapphire laser system are mixed in an AgGaS2 crystal using a noncollinear phase matching scheme. The relative bandwidth of the generated MIR pulse has been measured to be 23% of the central frequency, the broadest in DFM-based MIR sources reported thus far. It is found that a type-I crystal can yield a broader phase matching range of the spectrum than a type-II crystal within this scheme.

Generation of broadband mid-infrared pulses from an optical parametric amplifier

We report on the direct generation of broadband mid-IR pulses from an optical parametric amplifier. Several crystals with extended IR transparency, when pumped at 800 nm, display a broad phase-matching bandwidth around 1 mum, allowing for the generation of idler pulses spanning the 3-5 mum wavelength range. Using LiIO(3), we produce 2muJ pulses tunable in the 3-4 mum range with bandwidth supporting 30-fs transform-limited duration.

Generation and complete characterization of intense mid-infrared ultrashort pulses

Intense mid-infrared pulses tunable between 5 and 14 µm with pulse energies of several microjoules were generated by difference-frequency mixing (DFM) in a GaSe crystal. Longer wavelengths (up to 18 µm) were achieved by DFM in a CdSe crystal. The infrared pulses were then characterized using various techniques: The spectrum was measured using a Fourier-transform spectrometer, which was then modified to determine the interferometric second-order autocorrelation. The electric field spectral phase was measured using the same setup, thus leading to a full characterization of the mid-infrared pulses. The spectral phase was measured using the time-domain homodyne optical technique for spectral phase interferometry for direct electric field reconstruction, where spectral interferometry was replaced with time-domain interferometry. The measured pulse duration was 100 fs, nearly transform limited.

Low-Threshold Mid-Infrared Optical Parametric Oscillator UsingPeriodically Poled LiNbO3

We report the generation of tunable mid-infrared optical pulses usingall-solid-state pumped optical parametric oscillator in a periodicallypoled lithium niobate. Several ways were used to lower thethreshold, resulting in a mean threshold as low as 6.5 mW and anachievement of wavelength conversion in the 2.77–4.04 μm spectralrange. Continuous tuning range from 2.97 to 3.25 μm was achieved. Themaximum idler output power of 466 mW at the wavelength of 3.41 μm wasobtained, which represents an optical-to-optical conversion efficiencyof 19% from incident pump power to the idler output.

Compression of single-cycle mid-infrared pulses by Raman-active molecular modulators.

We show theoretically how high-order stimulated Raman scattering in the impulsive pump-probe regime can be used for generation of single mid-infrared (MIR) single-cycle pulses. The propagation of MIR probe pulses in a hollow waveguide filled with a Raman-excited gaseous medium, with a probe delay in the maximum of the molecular oscillations, results in spectral broadening covering almost 2 octaves. The spectral phases of this broadening can be compensated for by use of an output glass window with anomalous dispersion in the MIR. The spectral and temporal characteristics of the output pulses and the mechanism of pulse compression are studied by use of numerical and analytical solutions, and compression of a 70-fs input pulse at 4 microm to a single-cycle 6.5-fs output pulse is shown.

Generation of infrared radiation by stimulated Raman scattering in para-hydrogen crystal at 5 K.

We report the preliminary results of our experiments with stimulated Raman scattering in para-hydrogen crystal aimed at developing a continuously tunable laboratory laser source of mid-infrared radiation. With laser pulses at 532 nm, a conversion efficiency for the first Stokes beam of as much as 20% in the forward direction was observed through a single-pass, 5-cm-long crystal. Generation of mid-infrared pulses at 4.5 microm was achieved by use of the output of a near-infrared pulsed laser (1.6 microm, 3 ns), and an absorption spectrum of gaseous CD4 molecules was successfully recorded. These results suggest use of the solid para-hydrogen Raman shifter as a promising light source for mid-infrared spectroscopy.

Few-cycle mid-infrared pulse generation, characterization, and coherent propagation in optically dense media

The generation of four- to five-cycle mid-infrared pulses using a single-stage potassium niobate optical parametric amplifier (OPA) is demonstrated. The OPA is pumped by a gain-switched Ti:Sapphire regenerative amplifier and is seeded with the near-infrared portion of a white light continuum. The OPA is continuously tunable from 2700 to 4700 nm, and maintains sub-65 fs pulses that are fully characterized using cross-correlation frequency-resolved optical gating (XFROG). These are the shortest near-transform-limited pulses reported over this large infrared spectral range. This apparatus is used to measure ultrafast vibrational responses, specifically, pulse profiles modified by the free-induction decay (FID) of O–H oscillators. Both the intensity and instantaneous phase of these pulses are determined after traversing samples of isotopically diluted water (HDO in D2O) using XFROG, representing a new application of the XFROG technique to the study of (dipolar) molecular responses. Pronounced beating of the trailing edges of FID-modified pulses is observed even below optical densities of one, and the details of these features are found to depend on the chirp of the field used to generate the FID. These results indicate that discretion should be used in the selection of sample conditions for nonlinear infrared spectroscopic measurements.