Improved retrieval of complex supercontinuum pulses from XFROG traces using a ptychographic algorithm.

We demonstrate that time-domain ptychography, a recently introduced iterative ultrafast pulse retrieval algorithm, has properties well suited for the reconstruction of complex light pulses with large time-bandwidth products from a cross-correlation frequency-resolved optical gating (XFROG) measurement. It achieves temporal resolution on the scale of a single optical cycle using long probe pulses and low sampling rates. In comparison to existing algorithms, ptychography minimizes the data to be recorded and processed, and significantly reduces the computational time of the reconstruction. Experimentally, we measure the temporal waveform of an octave-spanning, 3.5 ps long, supercontinuum pulse generated in photonic crystal fiber, resolving features as short as 5.7 fs with sub-fs resolution and 30 dB dynamic range using 100 fs probe pulses and similarly large delay steps.

White light wavefront control with a spatial light modulator.

Spatial light modulators are ubiquitous tools for wavefront control and laser beam shaping but have traditionally been used with monochromatic sources due to the inherent wavelength dependence of the calibration process and subsequent phase manipulation. In this work we show that such devices can also be used to shape broadband sources without any wavelength dependence on the output beam's phase. We outline the principle mathematically and then demonstrate it experimentally using a supercontinuum source to shape rotating white-light Bessel beams carrying orbital angular momentum.

Generation of high quality, 1.3 cycle pulses by active phase control of an octave spanning supercontinuum.

Nonlinear pulse compression based on the generation of ultra-broadband supercontinuum (SC) in an all-normal dispersion photonic crystal fiber (ANDi PCF) is demonstrated. The highly coherent and smooth octave-spanning SC spectra are generated using 6 fs, 3 nJ pulses from a Ti:Sapphire oscillator for pumping a 13 mm piece of ANDi PCF. Applying active phase control has enabled the generation of 4.5 fs pulses. Additional spectral amplitude shaping has increased the bandwidth of the SC spectra further leading to nearly transform-limited pulses with a duration of 3.64 fs, which corresponds to only 1.3 optical cycles at a central wavelength of 810 nm. This is the shortest pulse duration achieved via compression of SC spectra generated in PCF to date. Due to the high stability and the smooth spectral intensity and phase distribution of the generated SC, an excellent temporal pulse quality exhibiting a pulse contrast of 14 dB with respect to the pre- and post-pulses is achieved.

High quality sub-two cycle pulses from compression of supercontinuum generated in all-normal dispersion photonic crystal fiber.

We demonstrate nonlinear pulse compression based on recently introduced highly coherent broadband supercontinuum (SC) generation in all-normal dispersion photonic crystal fiber (ANDi PCF). The special temporal properties of the octave-spanning SC spectra generated with 15 fs, 1.7 nJ pulses from a Ti:Sapphire oscillator in a 1.7 mm fiber piece allow the compression to 5.0 fs high quality pulses by linear chirp compensation with a compact chirped mirror compressor. This is the shortest pulse duration achieved to date from the external recompression of SC pulses generated in PCF. Numerical simulations in excellent agreement with the experimental results are used to discuss the scalability of the concept to the single-cycle regime employing active phase shaping. We show that previously reported limits to few-cycle pulse generation from compression of SC spectra generated in conventional PCF possessing one or more zero dispersion wavelengths do not apply for ANDi PCF.

Coherent octave spanning near-infrared and visible supercontinuum generation in all-normal dispersion photonic crystal fibers.

We present the first detailed demonstrations of octave-spanning SC generation in all-normal dispersion photonic crystal fibers (ANDi PCF) in the visible and near-infrared spectral regions. The resulting spectral profiles are extremely flat without significant fine structure and with excellent stability and coherence properties. The key benefit of SC generation in ANDi PCF is the conservation of a single ultrashort pulse in the time domain with smooth and recompressible phase distribution. For the first time we confirm the exceptional temporal properties of the generated SC pulses experimentally and demonstrate their applicability in ultrafast transient absorption spectroscopy. The experimental results are in excellent agreement with numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking. To our knowledge, we present the broadest spectra generated in the normal dispersion regime of an optical fiber.

Templated polar order of a guest in a quasiracemic organic host.

A quasiracemic mixture of Dianin's compound and its thiol derivative enforces additional anisotropy of the guest-accessible space, thus facilitating a net polar arrangement of guest molecules; guest alignment is rationalized in terms of van der Waals volume considerations.

Carbon Monoxide Triplet Rydberg Series in the f Complex Region.

Using a multistep state-selective excitation scheme, fluorescence-dip spectra of carbon monoxide have been recorded in the energy region between 106 100 and 112 200 cm(-1). Prominent groups of bands were tentatively identified as transitions into the 6f em leader10f (v=0) and 9psigma em leader11psigma (v=0) triplet Rydberg series. For the f complex states, molecular constants have been calculated. The triplet f levels show an unusually large rotational constant and are located at higher energies than their singlet counterparts. Copyright 2001 Academic Press.