Optical frequency combs: From frequency metrology to optical phase control

Abstract

The merging of continuous wave laser-based precision optical-frequency metrology with mode-locked ultrafast lasers has led to precision control of the visible and near-infrared frequency spectrum produced by mode-locked lasers. Such a phase-controlled mode-locked laser forms the foundation of a "femtosecond optical-frequency comb generator" with a regular comb of sharp lines with well-defined frequencies. For a comb with sufficiently broad bandwidth, it is now straightforward to determine the absolute frequencies of all of the comb lines. This ability has revolutionized optical-frequency metrology, synthesis, and optical atomic clocks. Precision femtosecond optical-frequency combs also have a major impact on time-domain applications, including carrier-envelope phase stabilization, synthesis of a single pulse from two independent lasers, nonlinear spectroscopy, and passive amplifiers based on empty external optical cavities. The authors first review the frequency-domain description of a mode-locked laser and the connection between the carrier-envelope phase and the frequency spectrum to provide a basis for understanding how the absolute frequencies can be determined and controlled. Using this understanding, applications in optical-frequency metrology and synthesis and optical atomic clocks are discussed. This is followed by discussions of time-domain experiments.

From a discrete to a continuous model for interpulse interference with a frequency-comb laser

“…As a result the accuracy of the frequency standard is transferred to the optical domain, with the frequency comb as transfer oscillator. These unique properties allow the frequency comb to be applied as a versatile tool, not only for time and frequency metrology [4][5][6][7], but also in fundamental physics [8,9], high-precision spectroscopy [10][11][12], and laser noise characterization [13][14][15]. The pulse-to-pulse phase relationship of the light emitted by the frequency comb has opened up new directions for long range highly accurate distance measurement [16][17][18][19][20][21][22][23].…”

Active control of bright electron beams with RF optics for femtosecond microscopy

“…8(b)]. For general deployment, the state-of-the-art PLL design has reached less than 1 fs timing precision between the laser and RF systems, 45,63 which can also be implemented here. However, a more pertinent issue is the longer time jitter incipient to the low frequency instabilities in the environment.…”

“…2(c). In the low-level RF system, the combined output of the voltage-controlled oscillator (VCO) and the RF synthesizer (Agilent E8247C) is synchronized with the laser oscillator pulse train at its 12th harmonics, 45 serving as the reference frequency, f Ref , through a PLL. Additional timing drift is corrected with a feedback temperature control by stabilizing the temperature of the RF components.…”

Invited Article: Concepts and tools for the evaluation of measurement uncertainty

“…In this case, the reference value would be the "the length of the path traveled by light in vacuum during a time interval of 1/299 792 458 of a second," which is 1 m by definition, 10 and may be realized using an iodine stabilized helium-neon laser 11 or optical frequency combs. 12,13 The comparison involved in measurement may be direct, as in the example just given, or it may be indirect, as when the volume of the box is determined by multiplying its length, width, and height, rather than by comparing the volume of the box against the volume of water that the box displaces when fully immersed in it.…”

“…The provenance of the glass fragments in this collection is as follows (with the number of fragments in each class between parentheses): float processed building windows (70), non-float processed building windows (76), float processed vehicle windows (17), containers (13), tableware (9), and headlamps (29). Contemporary windows are made of glass that, in its molten state, is poured onto a bed of molten metal (hence floated): this process, developed in the 1950s, produces glass sheets of very uniform thickness and superior flatness.…”