47 research outputs found
Parametrically polarization shaped pulses guided via a hollow core photonic crystal fiber for coherent control
We present ultrafast polarization pulse shaping through a micro structured
hollow core photonic crystal fiber. The pulses are shaped in pulse sequences
in which the energy, distance, phases, and chirps as well as the state of
polarization of each individual sub-pulse can be independently controlled. The
application of these pulses for coherent control is demonstrated for feedback
loop optimization of the multi-photon ionization of potassium dimers. In a
second experiment, this process is investigated by shaper-assisted pump–probe
spectroscopy which is likewise performed with pulses that are transmitted
through the fiber. Both techniques reveal the excitation pathway including the
dynamics in the participating electronic states and expose the relevance of
the polarization. These methods will be valuable for endoscopic applications
Phase sensitive pulse shaping for molecule selective three-photon excitation
In this paper we present a method for selective three-photon excitation of the
two dyes, p-Terphenyl (PTP) and BM-Terphenyl (BMT), in solution by using
shaped pulses. A good agreement between experiment and theoretical simulation
is obtained. With this method it is possible to achieve a considerable change
of the Fluorescence contrast between the two dyes which is relevant for
imaging applications of biological molecules
Spatial and temporal laser pulse shaping for two color excitation
Spatial and temporal laser pulse shaping is reported for two adjacent ranges of the laser spectrum. Thereto, two-photon excited fluorescence of dyes is measured for tailored pulses having two different spectral components which possess differently modulated spatial shapes. These particularly designed pulses are formed by using a 4f-temporal liquid crystal pulse shaper followed by a 2D-spatial shaper setup. Increased fluorescence contrasts between different dyes in a cuvette are recorded by selective phase shaping of the two adjacent spectral components. Moreover, two-photon excitation of the two spectral ranges from partially overlapping beams leads to spatially localized fluorescence in the overlap region. This is controlled by utilizing antisymmetric phase functions and can be applied to yield more complex two-photon excited fluorescence structures. The developed temporal and spatial shaping method of two-photon processes has valuable perspectives for optical and biophotonic applications
Parametrically shaped femtosecond pulses in the nonlinear regime obtained by reverse propagation in an optical fiber
We present the experimental realization of a method to generate predetermined,
arbitrary pulse shapes after transmission through an optical fiber in the
nonlinear regime. The method is based on simulating the reverse propagation of
the desired pulse shape in the fiber. First, linear and nonlinear parameters
of a single-mode step-index fiber required for the simulation are determined.
The calculated pulse shapes are then generated in a pulse shaper
Contrast improvement by using tailored laser pulses to circumvent undesired excitations
We report on fluorescence contrast improvement by using phase, amplitude, and polarization shaped laser pulses. The measurements were conducted by applying phase functions at different spectral amplitudes for excitations of dyes and agree very well with calculations. In particular, undesired one-photon excitations are circumvented with phase and amplitude tailored pulses for two-photon transition. This is realized by cutting out the laser spectrum at the wavelength of the one-photon process while utilizing an antisymmetric phase function that allows for constructive interference of the remaining outer spectral contributions for two-photon absorption. Moreover, polarization enhanced contrast between dyes is demonstrated where the two-photon dye is predominantly excited in one polarization direction and simultaneously the one-photon dye in the other polarization direction. The presented methods of shaping ultrashort laser pulses have a high potential for imaging applications
Influence of nonlinear effects on the three-photon excitation of L-Tryptophan in water using phase-shaped pulses
In its geometric form, the Maupertuis Principle states that the movement of a
classical particle in an external potential V(x) can be understood as a free
movement in a curved space with the metric gμν(x) = 2M[V(x) - E]δμν. We extend
this principle to the quantum regime by showing that the wavefunction of the
particle is governed by a Schrödinger equation of a free particle moving
through curved space. The kinetic operator is the Weyl-invariant
Laplace–Beltrami operator. On the basis of this observation, we calculate the
semiclassical expansion of the particle density
Simultaneous phase, amplitude, and polarization control of femtosecond laser pulses
We present a serial pulse shaper design which allows us to shape the phase,
amplitude, and polarization of fs laser pulses independently and
simultaneously. The capabilities of this setup are demonstrated by
implementing a method for generating parametrically tailored laser pulses.
This method is applied on the ionization of NaK molecules by feedback loop
optimization, employing a temporal sub pulse encoding. Moreover, we introduce
and characterize a further development of this common path pulse shaper scheme
for full control of all light field parameters
Enhance fluorescence signal by phase shaping
Here, we present a stage-scanning two-photon microscope (2PM) equipped with a temporal pulse shaper and a spatial light modulator enabling full control over spectral and spatial phases of the exciting laser pulse. We demonstrate the capability of correcting wavefronts and temporal pulse distortions without cross-dependencies induced by optical elements at the same time enhancing the fluorescence signal. We implemented phase resolved interferometric spectral modulation for temporal pulse shaping and the iterative feedback adaptive compensation technique for spatial pulse modulation as iterative techniques. Sample distortions were simulated by cover glass plates in the optical path and by chirping the exciting laser pulses. Optimization of the spectral and spatial phases results in a signal increase of 30% and nearly complete recovery of the losses. Applying a measured spatial compensation phase within a real leaf sample shows the enhancement in contrast due to wavefront shaping with local fluorescence increase up to 75%. The setup allows full independent control over spatial and spectral phases keeping or improving the spatial resolution of our microscope and provides the optimal tool for sensitive non-linear and coherent control microscopy
Selective excitation with shaped pulses transported through a fiber using reverse propagation
Reverse propagation is a numeric technique that makes it possible to obtain
arbitrarily shaped pulses after propagation through a fiber in the nonlinear
regime. We apply it to achieve selective two-photon excitation of dyes that
have overlapping absorption spectra with pulses transported through the fiber.
By comparing both contrast and signal level it is shown that phase and
amplitude shaped pulses generated using reverse propagation are superior to
pulses with antisymmetric phase despite loss caused by amplitude shaping