We have developed an epi-detected multimodal nonlinear optical microscopy platform based on a compact and cost-effective laser source featuring simultaneous acquisition of signals arising from hyperspectral coherent anti-Stokes Raman scattering (CARS), two-photon fluorescence, and second harmonic generation. The laser source is based on an approach using a frequency-doubled distributed Bragg reflector-tapered diode laser to pump a femtosecond Ti:sapphire laser. The operational parameters of the laser source are set to the optimum trade-off between the spectral and temporal requirements for these three modalities, achieving sufficient spectral resolution for CARS in the lipid region. The experimental results on a biological tissue reveal that the combination of the epi-detection scheme and the use of a compact diode-pumped femtosecond solid-state laser in the nonlinear optical microscope is promising for biomedical applications in a clinical environment.
We demonstrate a four-stage optical parametric chirped-pulse amplification system that delivers carrier-envelope phasestable
~1.5 μm pulses with energies up to 12.5 mJ before recompression. The system is based on a fusion of
femtosecond diode-pumped solid-state Yb technology and a picosecond 100 mJ Nd:YAG pump laser. Pulses with 62 nm
bandwidth are recompressed to a 74.4 fs duration close to the transform limit. To show the way toward a terawatt-peakpower
single-cycle IR source, we demonstrate self-compression of 2.2 mJ pulses down to 19.8 fs duration in a single
filament in argon with a 1.5 mJ output energy and 66% energy throughput.
In the presence of a high-intensity optical field, electrons are released from atoms on an attosecond time scale. Moreover,
in the tunnelling regime, this process displays a strong sensitivity to the carrier-envelope phase (CEP) of a few-cycle
light pulse. Tunnelling ionization - a fascinating quantum mechanical phenomenon - leads to a quasi-stepwise increase
of free electron density and, as a consequence, of the refractive index of the medium. These steps of the refractive index,
corresponding to half-cycles of the driving optical field, impose a transient attosecond phase mask. By scattering probe
light off this mask we detect quasi-periodic higher-order harmonics, the spectrum of which, unlike that of the harmonics
originating from intrinsic nonlinearity or driven by electron re-collisions, do not depend on the probe intensity and recollision
dynamics. The implemented noncollinear pump-probe experimental technique allows optical harmonics
generated due to a tunnelling-ionization-induced modulation of the electric current to be spatially separated from the
harmonics originating from atomic and ionic nonlinear susceptibilities, enabling background-free time-resolved detection
of electron-tunnelling-controlled harmonic spectra and offering an attractive solution for attosecond optical metrology of
gases and bulk solids.
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