Tigran Mansuryan

Parabolic temporal lensing and spectrotemporal imaging : a femtosecond optical oscilloscope

We introduce a self-reference method of parabolic temporal lensing and aberration-free spectrotemporal imaging for the direct measurements of femtosecond waveforms, with the goal of designing an ultrafast optical oscilloscope. Our method is based on dispersive stretching of the signal pulse and afterwards cancellation of the dispersion-induced phase in a quadratic nonlinear process by adding a reference parabolic phase (instead of Kerr lensing of traditional spectral compression). We have implemented the method through sum-frequency generation using the self-shaped nonlinear-dispersive similariton as a reference pulse and have demonstrated it experimentally for the direct measurements of amplitude- and phase-modulated pulses on a femtosecond time scale.

Pulse compression and fiber delivery of 45 fs Fourier transform limited pulses at 830 nm

A specific scheme is used for fiber delivery of ultrashort pulses using conventional elements. Starting from a standard femtosecond Ti:Al(2)O(3) oscillator (150 fs @ 830 nm), perfectly compressed ultrashort pulses with a duration of 45 fs are produced at the output of a standard two meter long single-mode fiber. The setup allows compensating independently and simultaneously second and third orders of chromatic dispersion as well as management of self-phase modulation in the fiber. It includes an optimized dispersion compensation line made of the assembly of diffraction gratings and prisms. The unsurpassed performances of the device are experimentally and numerically highlighted. Fiber delivery of sub-30 fs multinanojoule pulses is discussed.

Development of a real-time flexible multiphoton microendoscope for label-free imaging in a live animal

We present a two-photon microendoscope capable of in vivo label-free deep-tissue high-resolution fast imaging through a very long optical fiber. First, an advanced light-pulse spectro-temporal shaping device optimally precompensates for linear and nonlinear distortions occurring during propagation within the endoscopic fiber. This enables the delivery of sub-40-fs duration infrared excitation pulses at the output of 5 meters of fiber. Second, the endoscopic fiber is a custom-made double-clad polarization-maintaining photonic crystal fiber specifically designed to optimize the imaging resolution and the intrinsic luminescence backward collection. Third, a miniaturized fiber-scanner of 2.2 mm outer diameter allows simultaneous second harmonic generation (SHG) and two-photon excited autofluorescence (TPEF) imaging at 8 frames per second. This microendoscope’s transverse and axial resolutions amount respectively to 0.8 μm and 12 μm, with a field-of-view as large as 450 μm. This microendoscope’s unprecedented capabilities are validated during label-free imaging, ex vivo on various fixed human tissue samples, and in vivo on an anesthetized mouse kidney demonstrating an imaging penetration depth greater than 300 μm below the surface of the organ. The results reported in this manuscript confirm that nonlinear microendoscopy can become a valuable clinical tool for real-time in situ assessment of pathological states.

Ultrashort pulse fiber delivery with optimized dispersion control by reflection grisms at 800 nm

We experimentally demonstrate a compact and efficient arrangement for fiber delivery of sub-30 fs energetic light pulses at 800 nm. Pulses coming from a broadband Ti:Sapphire oscillator are negatively pre-chirped by a grism-pair stretcher that allows for the control of second and third orders of dispersion. At the direct exit of a 2.7-m long large mode area (LMA) photonic crystal fiber 1-nJ pulses are temporally compressed to 29 fs producing close to 30 kW of peak power. The tunability of the device is studied. Comparison between LMA fibers and standard SMF fibers is also discussed.

Development of a nonlinear fiber-optic spectrometer for human lung tissue exploration

Several major lung pathologies are characterized by early modifications of the extracellular matrix (ECM) fibrillar collagen and elastin network. We report here the development of a nonlinear fiber-optic spectrometer, compatible with an endoscopic use, primarily intended for the recording of second-harmonic generation (SHG) signal of collagen and two-photon excited fluorescence (2PEF) of both collagen and elastin. Fiber dispersion is accurately compensated by the use of a specific grism-pair stretcher, allowing laser pulse temporal width around 70 fs and excitation wavelength tunability from 790 to 900 nm. This spectrometer was used to investigate the excitation wavelength dependence (from 800 to 870 nm) of SHG and 2PEF spectra originating from ex vivo human lung tissue samples. The results were compared with spectral responses of collagen gel and elastin powder reference samples and also with data obtained using standard nonlinear microspectroscopy. The excitation-wavelength-tunable nonlinear fiber-optic spectrometer presented in this study allows performing nonlinear spectroscopy of human lung tissue ECM through the elastin 2PEF and the collagen SHG signals. This work opens the way to tunable excitation nonlinear endomicroscopy based on both distal scanning of a single optical fiber and proximal scanning of a fiber-optic bundle.

Spatially dispersive amplification in a 12-core fiber and femtosecond pulse synthesis by coherent spectral combining

A compact scheme is demonstrated for amplification and synthesis of ultrashort pulses by fiber amplifiers. Femtosecond pulses are split in 12 different spectral bands which are amplified separately in the 12 cores of a multicore ytterbium doped fiber. Combining the amplifier outputs together with the intensity and phase management of the spectral bands lead to short pulse synthesis with adjustable pulse shape. The scheme gave an x 92 enhancement in amplified power before the onset of nonlinear effects by comparison with standard stretcher free amplification in a single core fiber.

Spatially dispersive scheme for transmission and synthesis of femtosecond pulses through a multicore fiber

A new scheme is presented for fiber transmission of ultrashort laser pulses. A dispersive device divides the input pulses into spatially separated spectral components which are individually launched in the different channels of a multicore fiber before being recombined at the output by a second dispersive device. The parallel transmission of narrow spectral bands avoids self-phase modulation and could be appropriate to deliver high peak power pulses. Phase management of the spectral bands by an active element offers recovery of the seed pulse duration at the fiber output as well as pulse shaping capabilities. Both are reported in a proof of concept experiment using 190 fs input pulses and a 5 cores polarization maintaining fiber. Extension of the concept to femtosecond pulses amplification is suggested.

Self-forming of temporal dark soliton in spectral compressor

The spectral compressor completed by a spatial phase and amplitude mask placed in the dispersive delay line of spectral compressor modified it to the effective generator of dark solitons. Spectral evolution of generated dark soliton contains enough information about soliton character of the radiation.

Compact direct space-to-time pulse shaping with a phase-only spatial light modulator

A very compact and innovative pulse shaper is proposed and demonstrated. The standard architecture for pulse shaping that is composed of diffraction gratings associated with an amplitude-phase spatial light modulator (SLM) is replaced by a single phase-only SLM. It acts as a pulse stretcher and as an amplitude and phase modulator at the same time. Preliminary experiments demonstrate the accurate control of amplitude and phase of shaped pulses.

Nonlinear-Spectronic Similariton of Single-Mode Fiber without Gain

We demonstrate the forming of a similariton of nonlinear-spectronic nature in single-mode fiber without gain caused by combined impact of Kerr-nonlinearity and normal dispersion. Spectro-temporal similarity and imaging accuracy of the nonlinear-spectronic similariton are discussed.