Mark D. Moores

Simultaneous generation of spectrally distinct third harmonics in a photonic crystal fiber

By coupling femtosecond pulses at lambda - 1.55mum in a short length (Z - 95 cm) of photonic crystal fiber, we observe the simultaneous generation of two visible radiation components. Frequency-resolved optical gating experiments combined with analysis and modal simulations suggest that the mechanism for their generation is third-harmonic conversion of the fundamental pulse and its split Raman self-shifted component.

Adaptive Control of Pulse Phase In A Chirped Pulse Amplifier

Using experimental feedback, we demonstrate that a chirped-pulse amplifier can adaptively learn to compensate for the higher-order phase dispersion that is inherent in the amplification process. A genetic algorithm-based search routine is used to repetitively update the pulse phase in a programmable pulse stretcher during a plasma breakdown experiment to maximize the magnitude of spectral blueshift. Reductions in pulse duration from 37 to 30 fs and substantially better wing structure are typically obtained as a result of the optimization.

Adaptive control of femtosecond pulse propagation in optical fibers

Nonlinear effects present fundamental obstacles to the propagation of femtosecond pulses of detectable energy in single-mode optical fibers, inducing severe distortion even after a very short (a few meters) propagation distance. We show here that adaptive pulse shaping can overcome these limitations by synthesizing pulses that are self-correcting for higher-order nonlinear effects when they are launched in the fiber. This approach would not only affect optical communications but also yield benefits in various disciplines requiring optimized fiber-based femtosecond pulse delivery, for example, nonlinear imaging techniques such as multiphoton microscopy, material processing, and medical diagnostics.

Adaptive control methods for ultrafast pulse propagation in optical fibers

Adaptive control in combination with ultrafast pulse shaping provides a compelling approach to harness events that occur on the fastest timescale available. This paper illustrates the application of adaptive pulse shaping to femtosecond pulse propagation at /spl lambda/=1550 nm in single-mode optical fibers. The approach is illustrated first by through a numerical simulation of the technique. An experimental demonstration is described. The propagation of /spl sim/200-fs pulses is successfully achieved in the nonlinear regime by suitably preshaping the input pulse using an adaptive feedback loop.

Adaptive control of lasers and their interactions with matter

Summary form only given. We present several results obtained in our laboratory on the use of adaptive feedback methods in controlling lasers and their interactions with matter. First, we describe a genetic algorithm-based feedback loop for optimizing laser pulses in a femtosecond pump-probe experiment. In particular, we study the effectiveness of feedback control under a variety of experimental conditions. We find that for simple control experiments, feedback can achieve the desired goal even in the presence of experimental noise. Second, we describe experiments in which feedback is used to control the motion of charge carriers in quantum wells. Finally, we describe experiments in which adaptive feedback is used to compensate phase dispersion in chirped pulse amplifiers by monitoring the ionization rate of molecules in a spectral blueshift experiment.

Simultaneous generation of spectrally distinct third harmonic in photonic crystal fibers

Summary form only given. Recently, photonic crystal fibers have attracted considerable interest for their unique structure and optical properties. These fibers contain an ordered array of air holes which form a low-index cladding around a solid silica core. Other examples include fibers with hollow cores where light is guided by a photonic bandgap effect. Understanding the propagation of fs pulses in these fibers, and in particular the origin of nonlinear effects such as continuum generation, is important for optimizing their applications. In our experiments, we employ a 95 cm segment of fiber having a 2.5 micron silica core suspended in air by a web of sub-micron silica strand with a cladding diameter of 90 microns. 170 fs pulses from an optical parametric oscillator at a wavelength of 1550 nm of variable average power are coupled into the fiber. The output from the fiber is then analyzed spectrally and temporally and the fundamental pulses are sent to a frequency-resolved optical gating apparatus.

Femtosecond pulse delivery through single-mode optical fiber with adaptive pulse shaping

Summary form only given. Nonlinear effects present fundamental obstacles for the propagation of femtosecond pulses of detectable energy in single-mode optical fibers, inducing severe distortion even after a very short propagation distance. These effects are extremely hard to defeat or even predict. Adaptive pulse shaping can overcome these limitations by synthesizing pulses that are self-correcting for higher order nonlinear effects when launched in the fiber.

Generation of spectrally distinct third harmonic in photonic crystal fibers

By coupling femtosecond pulses at λ=1.55 microns in a one meter segment of photonic crystal fiber we observe simultaneous generation of third harmonic frequencies from both the fundamental and its self-shifted Raman component, whereas no second harmonic signal is detected.

Femtosecond pulse delivery through optical fibers with adaptive pulse shaping

Adaptive control is used to defeat nonlinear effects that severely distort ultrafast pulses during propagation through optical fibers.

Phase-shaped pulse propagation through turbid media

Summary form only given. Scattering in turbid media severely limits the coherent propagation of light and the ability to image. Many methods now exist for enhancing the contrast between coherent and scattered photons, among them optical coherence tomography, snake-light propagation, and photon density waves. We investigate the effect of phase-only pulse shaping on pulse propagation in turbid media. The work suggests that it may be possible to compensate for scattering in one dimension using phase-only pulse shaping as well as determine information about the underlying nature of the scattering process. In essence, the optical field trains itself to find the correct phase for optimal propagation and serves as a probe of the medium, teaching us (through transformations of the phase) about the nature of the scattering medium.