Christopher M. Nakamura

Precision control of carrier-envelope phase in grating based chirped pulse amplifiers.

It is demonstrated that the carrier-envelope (CE) phase of pulses from a high power ultrafast laser system with a grating-based stretcher and compressor can be stabilized to a root mean square (rms) value of 180 mrad over almost 2 hours, excluding a brief re-locking period. The stabilization was accomplished via feedback control of the grating separation in the stretcher. It shows that the long term CE phase stability of a grating based chirped pulse amplification system can be as good as that of lasers using a glass-block stretcher and a prism pair compressor. Moreover, by adjusting the grating separation to preset values, the relative CE phase could be locked to an arbitrary value in the range of 2pi. This method is better than using a pair of wedge plates to adjust the phase after the hollow-core fiber compressor. The CE phase stabilization after a hollow-core fiber compressor was confirmed by a CE-phase meter based on the measurement of the left-to-right asymmetry of electrons produced by above-threshold ionization.

Carrier-envelope phase stabilized 5.6fs, 1.2mJ pulses

The authors report the generation of 1.2mJ pulses with a duration of 5.6fs from a neon filled hollow-core fiber seeded with carrier-envelope phase stabilized 2.2mJ, 25fs pulses. The carrier-envelope phase after the fiber was measured by a second, out-loop f-to-2f interferometer. With seed pulse power locked, the carrier-envelope phase of the two-cycle pulses is controlled to a standard deviation of 370mrad. The peak power of the carrier-envelope phase stabilized pulses, 0.2TW, is twice that previously generated. The significance of seed pulse energy stability for carrier-envelope phase stabilization of few-cycle laser pulses is demonstrated.

Determining the phase-energy coupling coefficient in carrier-envelope phase measurements

By using two f-to-2f interferometers, we measured the phase-energy coupling coefficient for the first time. The results reveal that a 1% in-loop laser energy change causes a 160 mrad carrier-envelope phase shift to output pulses.

Mechanism of phase-energy coupling in f-to-2f interferometry.

White-light generation has been used widely in single-shot f-to-2f interferometers for stabilizing the carrier-envelope (CE) phase of laser amplifiers. The accuracy of the relative phase values measured by such an interferometer is affected by fluctuations in the laser pulse energy. A simple two-step model is proposed to explain the mechanism that couples the laser energy and the CE phase. The model explains the experimentally observed dependence of the group delay between the f and the 2f pulses on the laser energy, as well as the CE phase shift caused by the pulse energy variation.

Carrier envelope phase effects on polarization gated attosecond spectra

Polarization gated high harmonic generation in argon gas was phase matched to produce a single or double pulses with 104 photons. It was accomplished by optimizing the argon gas pressure. The spectrum interference of the two pulses is affected by the carrier-envelope phase like in Youngs experiments. The XUV flux is sufficient for measuring the single shot XUV spectrum in the 33eV-55eV photon energy range. The spectral profile was a super-continuum for some shots and showed discrete high harmonics peaks for other shots. The carrier-envelope phase of pulses from grating-based chirped pulse amplification was also varied smoothly to cover a 2π range by controlling the grating separation. It is demonstrated that XUV spectra measures both the absolute value of the phase and the stability of the phase by measuring the phase with an f-to-2f setup and by the variation of XUV spectra from polarization gated high harmonics generation.

Pilot Testing of the Pathway Active Learning Environment

We present an initial analysis of data taken to test the technical functionality and student usability of an interactive synthetic tutoring system administered online. The system allows students to ask questions and receive prerecorded video responses from knowledgeable tutors in real‐time. It logs student interactions with a timestamp and username to generate a time‐resolved picture of students’ use of the system. The tutoring interaction is structured by lessons covering Newton’s laws. Time on‐task estimates indicate that students spent about 2.5 hours working through our materials, about as much as intended. Data show students’ reluctance to query the tutor or that their focus is on other aspects of the system. This suggests modifications to the system that may encourage students to take advantage of its interactive capabilities. The system combines lessons, images, and video technology designed to emulate conversation to produce a supplemental teaching tool that may be useful for studying multimedia e...

Online Data Collection and Analysis in Introductory Physics

Online implementation of physics learning materials may present a powerful method of data collection for physics education research, in addition to being useful for supplemental instruction. This may have implications for composite instruction and research designs. We have developed three lessons on Newton’s laws and implemented them on the Internet. The lessons ask students to make observations and measurements using video clips, perform calculations and answer open‐ended questions. Responses are collected via an online response system. One hundred ten university students enrolled in an algebra‐based physics course and 30 high school physics students worked through some or all of our lessons, and their responses were collected. We present a qualitative and quantitative analysis of their responses and assess the implications for optimal design of online lesson materials for collecting meaningful data about students’ understanding of basic physics concepts.

Carrier-envelope phase stabilized 5.6 fs, 1.2 mJ pulses

Carrier-envelope phase stabilized 1.2 mJ pulses with duration of 5.6 fs were obtained from a Ne filled hollow-core fiber. With power locking the phase is controlled to 370 mrad measured by out-loop f-to-2f interferometery.

Laser power locking for improvement of carrier-envelope phase stability

The pulse energy fluctuation of a kilohertz femtosecond laser was reduced from 1.33% RMS to 0.28% RMS, which improves the carrier-envelope phase stability from 500 mrad to 200 mrad.

Determining Phase-Energy Coupling Coefficient in Carrier-envelope Phase Measurements

By using two f-to-2f interferometers, we measured the phase-energy coupling coefficient for the first time. The results reveal that a 1% in-loop laser energy change causes a 160 mrad carrier-envelope phase shift to output pulses.