Sub-micron tapered fibers have been proposed to be a suitable platform for the implementation of third-order spontaneous parametric down conversion (TOSPDC). Starting with the derivation of expressions for quantized fields in optical fibers, we devise an exact theoretical treatment of the expected triplet generation rate.
Overcoming technical performance limitations in the detection and characterization of terahertz (THz) radiation will enable ground-breaking scientific advances from the study of fast and non-reproducible phenomena to enabling THz quantum applications that require single-photon sensitivity. Electro-optic sampling techniques intrinsically rely on the acquisition of multiple data points to reconstruct the full THz waveform, which leads to long data acquisition times, and prevents the detection of single photons. We have developed two distinct and highly sensitive detection techniques for pulsed THz radiation: i) a single-pulse measurement which employs chirped-pulse spectral encoding and a dispersive Fourier transform method for time-resolved THz spectroscopy at a demonstrated rate of 50 kHz; and ii) a single-THz-photon detection technique based on parametric frequency conversion and single-photon counting technology capable of detecting THz pulses at the zeptojoule level. These extreme detection schemes will lay the foundation for THz applications in the single-pulse and single-photon regimes.
We report the first-ever observation of optomagnetically-driven rotation of a magnetic particle, optically levitated inside a chiral hollow-core photonic crystal fibre (HC-PCF). Rotation of the optically biaxial particle causes a change in the transmitted power and ellipticity of a linearly polarised probe beam at 632.8 nm. HC-PCF offers a versatile platform for investigating the optomechanical response of levitated magnetic particles.
Dispersive Fourier method gives access to spectral information by mapping them in the time domain. This facilitates shot-to-shot spectroscopy of rapidly changing systems. We adapted this technique to demonstrate time-resolved THz spectroscopy at 50 kHz repetition rate by encoding the THz waveform onto the spectral components of spectrally broadened (NIR) ultrafast laser pulses.
The rapid acquisition of terahertz (THz) time-domain waveforms is a significant challenge in the study of fast and non-reproducible phenomena. To increase data acquisition rates, the THz waveform can be encoded on spectral components of individual near-infrared (NIR) ultrafast laser pulses. By using dispersive Fourier transform method, where spectral information are mapped in the time domain, we demonstrate time-resolved THz-spectroscopy at an unprecedented rate of 50 kHz. With this technique, we resolve sub-millisecond dynamics of carriers in silicon injected by successive resonant pulses as a saturation density is established.
Non-classical correlated twin beams can be generated through the modulational instability in a hollow-core photonic crystal fibre filled with a noble gas. Since the gain is provided by a monatomic gas, the influence of Raman effect, which is typical for fibre-based sources of entangled photons, is avoided. Additionally, the gas pressure together with the frequency chirp of the input pump pulse allow continuous tuning of the number of frequency modes of the twin beams. We combine spectral interferometry and single-shot measurement to retrieve the phase of the noise-driven generated sidebands.
Non-linear optical microscopy proves to be an indispensable tool in natural sciences and becomes more and more attractive for clinical applications. Coherent Raman scattering, for instance, has the potential to become an in-vivo fast label-free histology tool as its chemical selectivity provides quantitative information on lipids and proteins locations and concentrations in tissues. Along with these techniques, second-harmonic generation of collagen and 2-photon excitation fluorescence broaden even more the non-linear imaging ability as collagen fibers represent an important role in human body construction. Whilst 2-photon excitation fluorescence allows to study auto-fluorescence (ex. NADH and NADHP molecules), and to excite a vast range of chromophores. However, absorption and scattering limit significantly the nonlinear imaging depth into tissues. As a solution, we offer a flexible, compact, and multimodal nonlinear endoscope (2.2 mm outer diameter, 35 mm rigid length) based on a resonantly piezo scanned hollow-core negative curvature double-clad fiber. The fiber design allows distortion-less, background-free delivery of femtosecond excitation pulses and the back-collection of nonlinear signals through the same fiber. The double-cladding of this fiber attends 10^5μm of silica collection surface which allows for a 4-fold collection improvement compared to previously used Kagomé hollow core fibers. Having a good control on the resonantly scanning fiber the endoscope can perform nonlinear imaging up to 8 frames per second over a field of view of 400μm. We demonstrate 2photon, SHG and CARS imaging in ex vivo gastric human tissue samples and in-vivo 2-photon fluorescence imaging of GFP-labeled neurons in mouse brain.
Over the last two decades the interest in photonic crystal fiber (PCF) has grown considerably, particularly in nonlinear optics where it allows enhanced control over the dispersion landscape. Although silica is the material most commonly used to fabricate PCF, its limited window of transmission and its susceptibility to optical damage at wavelengths below ~350nm is driving the development of fibers made from glasses with transmission windows extending into the deep ultraviolet and the mid-infrared. An alternative is offered by gas-filled hollow-core fiber, in which the light propagates predominantly in the gas.
In kagomé-style hollow-core PCF filled with noble gas, the weak anomalous dispersion of the empty fiber is balanced by the normal dispersion of the filling gas, resulting in a versatile system whose dispersion landscape can be adjusted in real time [Travers et al., JOSAB 28, A11 (2011)]. Under appropriate conditions the launched pulse undergoes soliton self-compression followed by emission of a band of dispersive radiation in the UV. UV light tunable down to 113 nm has been generated with this technique [Russell et al., Nat. Photon. 8, 278 (2014)].
Solid-core ZBLAN (fluorozirconate) glass PCF is transparent from 0.2 to ~7.8µm. Launching ~1nJ 140fs pulses at 1µm wavelength into a ~1µm diameter core resulted, after 4cm of propagation, in generation of a supercontinuum spectrum extending from ~210nm to beyond 2µm. In strong contrast to silica PCF, the ZBLAN PCF showed no signs of any solarization-related damage, even when operating over many hours [Jiang et al., Nat. Photon. 9, 133 (2015)].
We report recent advances in the domain of Highly Non-Linear Photonic Crystal Fibers (HNL-PCFs) especially designed as gain medium for Raman fiber lasers. Indeed, a fiber Raman coefficient as high as 42 W-1.km-1 at 1.12μm has been obtained, while keeping optical losses moderate, below 6 dB/km at this wavelength. We have calculated that only 2 meters of such a germanium doped HNL-PCF is required to obtain an output power in the order of 10W at 1.12 μm with an efficiency of 90%. Experimental output optical spectra of multi-cascades cavities are finally given.
We demonstrate a Raman laser made from a grating-free highly-nonlinear photonic crystal fiber. The laser
threshold power is lower than 600 mW and laser power characteristics recorded in experiments are accurately
described from the usual simplest model dealing only with stationary evolutions of total optical powers. Experimental
investigations of the spectral properties of our grating-free Raman fiber laser evidence that the shape
of the Stokes power spectrum remains remarkably Gaussian whatever the incident pump power. Increasing the
incident pump power induces a drift of the Stokes wavelength together with a broadening of the Stokes optical
spectrum. Investigations on the role of light polarization on laser characteristics show that our grating-free
Raman fiber laser behaves as a Raman laser made with a standard polarization maintaining fiber. At high pump
power, the birth of the second-order Stokes wave induces a destabilization of the laser output with the emergence
of self-oscillations of the optical powers which are explained from the interplay between counterpropagating pump
and Stokes waves through stimulated Raman scattering.
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