Biomedical subjects

Steven T Cundiff

Publications and source records attributed to Steven T Cundiff.

11 recordsLinked to original sources

PubMed2006

Synchronization of mode-locked femtosecond lasers through a fiber link.

Two mode-locked femtosecond fiber lasers, connected via a 7 km fiber link, are synchronized to an rms timing jitter of 19 fs, observed over the entire Nyquist bandwidth (half of the 93 MHz repetition frequency). This result is achieved in two steps. First, active cancellation of the fiber-transmission noise reduces timing jitter caused by path length fluctuations to a record level of 16 fs. Second, using a wide bandwidth interactivity actuator, the slave laser is synchronized to the incoming stable pulse train from the reference laser to within 10 fs. These results are confirmed by an optical cross-correlation measurement performed independently of the feedback loop operated in the microwave domain.

Journal Article↗

PubMed2006

Noise-induced linewidth in frequency combs.

Frequency combs generated by trains of pulses emitted from mode-locked lasers are analyzed when the center time and phase of the pulses undergo noise-induced random walk, which broadens the comb lines. Asymptotic analysis and computation reveal that, when the standard deviation of the center-time jitter of the nth pulse scales as n(p/2) where p is a jitter exponent, the linewidth of the kth comb line scales as k(2/p). The linear-dispersionless (p=1) and pure-soliton (p=3) dynamics in lasers are derived as special cases of this time-frequency duality relation. In addition, the linewidth induced by phase jitter decreases with power P(out), as (P(out))(-1/p).

Journal Article↗

PubMed2006

Many-body interactions in semiconductors probed by optical two-dimensional fourier transform spectroscopy.

We study many-body interactions between excitons in semiconductors by applying the powerful technique of optical two-dimensional Fourier transform spectroscopy. A two-dimensional spectrum correlates the phase (frequency) evolution of the nonlinear polarization field during the initial evolution and the final detection period. A single two-dimensional spectrum can identify couplings between resonances, separate quantum mechanical pathways, and distinguish among microscopic many-body interactions.

Journal Article↗

PubMed2005

Mode-locked fiber laser frequency-controlled with an intracavity electro-optic modulator.

We demonstrate a mode-locked, erbium-doped fiber laser with its repetition frequency synchronized to a second fiber laser via an intracavity electro-optic modulator (EOM). With servo control from the EOM (bandwidth approximately 230 kHz) and a slower speed intracavity piezoelectric transducer (resonance at approximately 20 kHz), we demonstrate stabilization of the repetition frequency with an in-loop rms timing jitter of 10 fs, integrated over a bandwidth from 1 Hz to 100 kHz. This represents what is to our knowledge the first time an EOM has been introduced inside a mode-locked laser cavity for fast servo action and the lowest timing jitter reported for a mode-locked fiber laser.

Journal Article↗

PubMed2005

Interference effects in transient Kerr spectra of a semiconductor multilayer structure.

We experimentally study the spectra of the transient Faraday and Kerr effects near exciton resonances of a GaAs multiple quantum well. A multilayer calculation with a transfer matrix model accounts quantitatively for the linear transmission (reflectivity) spectra and the Faraday (Kerr) spectra. The Faraday and Kerr spectra do not obey a Kramers-Kronig relation. This phenomenon was found to be due to the multiple reflection effects on the Kerr spectra.

Journal Article↗

PubMed2005

Impulsive stimulated Raman scattering: comparison between phase-sensitive and spectrally filtered techniques.

Impulsive stimulated Raman scattering is used to generate and control coherent phonons and other low-frequency modes. In transparent materials, pump-probe experiments are usually performed by spectrally resolving the probe beam and measuring the spectral shift as a function of pump-probe time delay. By measuring the optical phase of the probe pulse as a function of time delay, we find that the phonon signal can be increased by a factor alpha(omegadelta)(-1), where omega is the phonon frequency and delta is the pulse duration.

Algorithms↗

PubMed2004

Carrier-envelope phase slip of ultrashort dispersion-managed solitons.

The carrier-envelope phase slip of an ultrashort pulse circulating in a mode-locked Ti:sapphire laser is analyzed. The laser cavity is modeled by a dispersion- and nonlinearity-managed nonlinear Schrödinger equation. The combined contributions to the phase slip induced by nonlinear phase and nonlinear dispersion are found to approach zero for strong dispersion maps. The dependence of the slip on third-order dispersion is found as well. The analytical results are verified using numerical simulations.

Journal Article↗

PubMed2004

Nonlinear effects on the carrier-envelope phase.

Calculations, using the Maxwell equations, are presented of nonlinear effects on the carrier-envelope phase for pulse durations in the two-optical-cycle range for pulses propagating in sapphire. Initially, with increasing pulse intensity the carrier-envelope phase increases monotonically. However, at higher intensities there is a turnabout in the direction of the phase change and a large change in the phase that is caused by a warping of the envelope from strong nonlinear effects. The Kerr nonlinear response occurs on a time scale of approximately 1 fs and gives significantly different results from those obtained by assuming an instantaneous response.

Journal Article↗

PubMed2003

Intensity-related dynamics of femtosecond frequency combs.

We have performed systematic studies of intensity-related dynamics of the pulse repetition and carrier-envelope offset frequencies in mode-locked Ti:sapphire lasers. We compared the results far two laser systems that have different intracavity dispersion-compensation schemes. We found that the carrier-envelope phase noise and its dynamic response depend critically on the mode-locking conditions. An intensity-related shift of the laser spectrum was found to be instrumental in interpretations.

Journal Article↗

PubMed2002

Brewster's angle attenuator for terahertz pulses.

A variable attenuator for terahertz (THz) pulses is developed on the basis of the change in reflectivity of lithium niobate wafers with incident angle in a Brewster configuration. We can vary the THz field transmission from 22% to 54%, a change of a factor of 2.5, while preserving the shape of the THz pulse spectrum. Changes in the THz spectrum are shown to be much smaller when the Brewster attenuator is used than when either the near-infrared pump power or the bias voltage on a THz photoconductive antenna is varied. The Brewster attenuator should prove especially useful for varying THz field strength in nonlinear optical studies that use broadband THz pulses.

Journal Article↗

PubMed2002

Experimental evidence for soliton explosions.

We show, experimentally and numerically, that Ti:sapphire mode-locked lasers can operate in a regime in which they intermittently produce exploding solitons. This happens when the laser operates near a critical point. Explosions happen spontaneously, but external perturbations can trigger them. In stable operation, all explosions have similar features, but are not identical. The characteristics of the explosions depend on the intracavity dispersion.

Journal Article↗