R. J. Jones

Output coupling methods for cavity-based high-harmonic generation

We have investigated the coupling efficiency and cavity loss associated with a ring cavity that has a hole in one of the focusing mirrors. The aperture provides a means through which intracavity high-harmonic generation can be coupled from the cavity. By studying different cavity geometries and input modes we have found that the integration of phase-plates on the focusing mirrors provides the best performance in terms of input coupling efficiency, cavity loss, and output-coupling of the generated high harmonic light.

Precise measurements of optical cavity dispersion and mirror coating properties via femtosecond combs

We precisely determine the dispersion of an optical cavity over a large spectral bandwidth using a broadband optical comb generated by a femtosecond laser. This approach permits the effective characterization of the next generation of mirrors that will offer high reflectivity, minimal absorption/scattering loss, and well-defined dispersion characteristics. Such mirrors are essential for constructing passive, high-finesse cavities capable of storing and enhancing ultrashort pulses and for exploring novel intracavity-based experiments in atomic and molecular spectroscopy and extreme nonlinear optics. We characterize both zero and negative group-delay-dispersion mirrors and compare their performance against the targeted coating design. The high sensitivity of this approach is demonstrated with a precise determination of the group-delay dispersion of air inside a 40-cm long optical cavity, demonstrating an accuracy better than 1 fs2.

Intensity-related dynamics of feintosecond 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.

High-repetition-rate coherent femtosecond pulse amplification with an external passive optical cavity.

We demonstrate a general technique for enhancement of femtosecond pulses from a pulse train through their coherent buildup inside a high-finesse cavity. Periodic extraction of the intracavity pulse by means of a fast switch provides a net energy gain of 42 to >70 times for 38-58-fs pulse durations. Starting with an actively stabilized but otherwise standard mode-locked laser system, we demonstrate pulses of >200-nJ energy.

Investigation of a grating-based stretcher/compressor for carrier-envelope phase stabilized fs pulses.

In this work, we experimentally investigate the effect of a grating based pulse stretcher/compressor on the carrier-envelope phase stability of femtosecond pulses. Grating based stretcher-compressor (SC) setups have been avoided in past demonstrations of chirped pulse amplification (CPA) of carrier envelope phase (CEP) stabilized femtosecond pulses, because they were expected to introduce significantly stronger CEP fluctuations than material-based SC systems. Using a microstructure fiber-based detection setup, we measure CEP fluctuations of PhiCE,SC = 340 milliradians rms for a frequency range from 63 mHz to 102 kHz for pulses propagating through the SC setup. When bypassing the beam path through the SC, we find CEP fluctuations of PhiCE,bypass = 250 milliradians rms. These values contain significant contributions from amplitude-to-phase conversion in our microstructure fiber-based detection setup for PhiCE. Hence, we do not unambiguously measure any added CEP noise intrinsic to the SC setup. To distinguish between intrinsic SC effects and amplitude-to-phase conversion, we introduce controlled beam pointing fluctuations alpha and again compare the phase noise introduced when passing through / bypassing the SC. Our measurements do not reveal any intrinsic effects of the SC system, but allow us to place an upper limit on the sensitivity of our SC system of PhiCEintrinsic,SC / alpha < 13000 rad/rad. Our results demonstrate experimentally that there is not a strong coupling mechanism between CEP and beam pointing through a stretcher/compressor , as well as measuring significantly smaller CEP fluctuations than experimental results reported previously.

Nonlinear dynamics inside femtosecond enhancement cavities

We have investigated the effect of intracavity nonlinear dynamics arising from enhanced peak powers of femtosecond pulses inside broad-bandwidth, dispersion-controlled, high-finesse optical cavities. We find that for chi(3) nonlinearities, when a train of femtosecond pulses are maximally coupled into a cavity by active stabilization of its frequency comb to the corresponding linear resonances of a cavity, enhancement ceases when the peak nonlinear phase shift is sufficient to shift the cavity resonance frequencies by more than a cavity linewidth. In addition, we study and account for the complex spectral dynamics that result from chirping the input pulse and show excellent qualitative agreement with experimental results.

Femtosecond enhancement cavity — direct frequency comb spectroscopy and coherent extreme nonlinear optics

To prepare for future experiments on coherent spectroscopy and quantum control in the VUV spectral regions, we have pursued direct frequency comb spectroscopy and generation of phase coherent VUV frequency combs. High-finesse, low-dispersion passive optical cavities are used to enhance the power of femtosecond pulses for extreme nonlinear optics and to increase detection sensitivity for spectroscopy.

Ultra-Precise Phase Control of Short Pulses - Applications to Nonlinear Spectroscopy

Precise phase control of femtosecond lasers has become increasingly important as novel applications utilizing the femtosecond laser-based optical comb are developed that require greater levels of precision and higher degrees of control [1]. Improved stability is beneficial for both “frequency domain” applications, where the relative phase or “chirp” between comb components is unimportant (e.g. optical frequency metrology), and, perhaps more importantly, “time domain” applications where the pulse shape and/or duration is vital, such as in nonlinear optical interactions [2]. For both types of applications, minimizing jitter in the pulse train and noise in the carrier-envelope phase is often critical to achieve the desired level of precision. Phase-stabilized mode-locked femtosecond lasers have played a key role in recent advances in optical frequency measurement [3,4], carrier-envelope phase stabilization [2,5,6], alloptical atomic clocks [7,8], optical frequency synthesizers [9], coherent pulse synthesis [10], and ultra-broad, phase coherent spectral generation [11]. The capability of absolute optical frequency measurements in the visible and IR spectral regions adds a new meaning to the term of precision molecular spectroscopy. Understanding of molecular structure and dynamics often involves detailed spectral analysis over a broad wavelength range. Such a task can now be accomplished with a desired level of accuracy uniformly across all relevant spectral windows, allowing precise investigations of minute changes in the molecular structure over a large dynamic range. For example, absolute frequency measurement of vibration overtone transitions and other related

Control of coherent light and its broad applications

A remarkable synergy has been formed between precision optical frequency metrology and ultrafast laser science. This has resulted in control of the frequency spectrum produced by mode-locked lasers, which consists of a regular “comb” of sharp lines. Such a controlled mode-locked laser is a “femtosecond optical frequency comb generator.” For a sufficiently broad comb, it is straightforward to determine the absolute frequencies of all of the comb lines. This ability has revolutionized optical frequency metrology and synthesis, and it has also led to recent demonstrations of atomic clocks based on optical frequency transitions. In addition, the comb technology is having a strong impact on time-domain applications, including control of the carrier-envelope phase, precision timing synchronization, and synthesis of a single pulse from independent lasers.

From relative to absolute: optical phase measurement and control in ultrashort pulses

Summary form only given. A phase stabilized frequency comb spanning an entire optical octave (>300 THz) has been established, leading to a single step, phase coherent connection between the optical and radiofrequency spectral domains. The precision comb can also serve as an accurate gear-box to transfer the oscillatory information of a laser stabilized by a high quality optical transition down to the microwave/rf domain, thereby establishing a simple optical atomic clock. We present one of the systems based on an optical transition of iodine molecules, providing an rf clock signal with a frequency stability comparable to that of an optical standard, and that is superior to almost all conventional rf sources. To realize a high-power CW optical frequency synthesizer, a separate widely tunable single-frequency cw laser has been employed to randomly access the stabilized optical comb and lock to any desired comb component.