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We demonstrate how pulse energy in hollow-core fiber can be scaled beyond gas-ionization limitations using divided-pulse nonlinear compression. With one pulse, ionization limits our fiber’s output pulse energy to 2.7 mJ at an input of 4 mJ. By dividing the pulse to four low-energy pulses before the fiber, we eliminated the ionization and scaled the pulse energy 2.5× to 6.6 mJ at an input energy of 10 mJ. Larger energy scaling is possible, as our maximum pulse energy has not reached the new gas ionization threshold. Our results motivate applying the method to state-of-the-art systems for large pulse energy scaling without prohibitive system size increases.

We simulate Kerr and plasma nonlinearities in a hollow-core fiber to show how plasma effects degrade the output pulse. Our simulations predict the plasma effects can be avoided entirely by implementing divided-pulse nonlinear compression. In divided-pulse nonlinear compression, a high-energy pulse is divided into multiple low-energy pulses, which are spectrally broadened in the hollow-core fiber and then recombined into a high-energy, spectrally broadened pulse. With the plasma effects overcome, spectral broadening can be scaled to larger broadening factors and higher pulse energies. We anticipate this method will also be useful to scale spectral broadening in gas-filled multipass cells.

We experimentally demonstrate how divided-pulse nonlinear compression can be used to improve the temporal contrast of a laser pulse train while simultaneously temporally compressing the pulses. We measure a contrast improvement of almost four orders of magnitude on a nanosecond time scale and temporally compress the pulses from 1.2 ps to 187 fs. The efficiency of our method is also competitive with other contrast improvement methods, with 72% efficiency measured for the main pulse. We expect the method will be useful in the continuing development of high-power, Yb regenerative amplifiers, which suffer from both significant prepulses and relatively long pulse durations.

We present an analytic model that describes the output pulse after Kerr-based spectral broadening with divided-pulse nonlinear compression that includes errors in unequal pulse division, birefringent plate retardance, and thermal drift. The model shows that alignment tolerances become impractically tight at high levels of nonlinearity and that the angle of incidence on the birefringent plates can be utilized as a compensator to loosen those tolerances. We present experimental verification of the model, which is expected to be a fast and flexible tool to design future divided-pulse nonlinear compression systems.

An advanced focusing scheme, called a “flying focus,” uses a chromatic focusing system combined with a broadband laser pulse with its colors arranged in time to propagate a high intensity focus over a distance that can be much greater than its Rayleigh length while decoupling the speed at which the peak intensity propagates from its group velocity. The flying focus generates a short effective pulse duration with a small diameter focal spot that co- or counter-propagates along the optical axis at any velocity. Experiments validating the concept measured subluminal (−0.09c) to superluminal (39c) focal spot velocities with a nearly constant peak intensity over 4.5 mm. Experiments that increased the peak intensity above the ionization threshold for gas demonstrated ionization waves propagating at the velocity of the flying focus. These ionization waves of any velocity overcome several laser-plasma propagation issues, including ionization-induced refraction. The flying focus presents opportunities to overcome current fundamental limitations in laser-plasma amplifiers, laser wakefield accelerators, photon accelerators, and high-order frequency conversion.An advanced focusing scheme, called a “flying focus,” uses a chromatic focusing system combined with a broadband laser pulse with its colors arranged in time to propagate a high intensity focus over a distance that can be much greater than its Rayleigh length while decoupling the speed at which the peak intensity propagates from its group velocity. The flying focus generates a short effective pulse duration with a small diameter focal spot that co- or counter-propagates along the optical axis at any velocity. Experiments validating the concept measured subluminal (−0.09c) to superluminal (39c) focal spot velocities with a nearly constant peak intensity over 4.5 mm. Experiments that increased the peak intensity above the ionization threshold for gas demonstrated ionization waves propagating at the velocity of the flying focus. These ionization waves of any velocity overcome several laser-plasma propagation issues, including ionization-induced refraction. The flying focus presents opportunities to overcome ...

Temporal masking of clicks by noise was investigated using forward and backward masking paradigms. Both the noise duration and the temporal separation, Δt, between the click and the noise were varied. For very brief Δt's (100 μsec) and for very long Δt's (100 μsec) the duration of the masker did not greatly affect the click threshold. However, for intermediate Δt's, the threshold of the click increased by as much as 44 dB as the noise duration increased from 0.1 to 100 msec. Temporal weighting functions, which describe the relative effectiveness of the noise as a function of Δt, were computed from these data.

Experiments were performed to compare lateralization of combination tones with that of pure tones under comparable masking conditions. Two primary tones f1 and f2 at 70 dB SPL were employed. The frequency of f1 was 620 Hz, and f2 ranged from 1.1 f1 to 1.5 f1. Phase and amplitude of the cubic difference tone, 2 f1 − f2, were first determined monaurally using an objective forced‐choice procedure. These monaural measurements were then used to specify the phase and amplitude of the lateralization tone in the binaural experiment. The two primaries were introduced to one ear and the externally produced lateralization tone of frequency 2 f1 − f2 to the other. Subjects were required to discriminate a change in phase of the lateralization tone in an oddity procedure. In the control condition, in order to simulate the combination tone, an externally generated tone of frequency 2 f1 − f2 was administered in the presence of a 70‐dB masking tone of frequency f1. The amplitude of the simulated combination tone was esti...

A three‐alternative forced‐choice procedure was employed to measure monaurally the phase and amplitude of the cubic combination tone, 2 f1 − f2. To measure phase, two primaries f1 and f2 were presented simultaneously with a third tone at frequency 2 f1 − f2. The third tone had phase θ in two intervals and phase θ + 180° in the third interval. A plot of percent correct discrimination as a function of θ was used to determine the phase of the combination tone. The phase of the combination tone was calculated to be ±90° from the value of θ which resulted in minimum discrimination. A “mirroring” technique was then employed to determine the amplitude of the combination tone. In the odd interval a cancellation tone was added 180° out of phase from the combination tone. Percent correct discrimination was measured as a function of the level of the cancellation tone. It was assumed the minimum in the function occurred at a level 6 dB greater than the combination tone. The results obtained from various objective and...