Volume 5 Issue 4, April 2011

Frequency combs — broadband phase-coherent optical sources — are finding an increasing number of new applications in the field of metrology.

This year celebrates the twentieth anniversary of frequency-resolved optical gating — the first and most general technique for measuring ultrashort laser pulses.

Frequency combs generated by femtosecond lasers are powerful tools for high-precision optical spectroscopy and metrology. Theodor Hänsch, who received part of the Nobel Prize for Physics in 2005 for his work in this field, spoke to Nature Photonics about how frequency combs have changed science.

The successful integration of a single-photon source with a slow-light medium creates important opportunities for photon synchronization and marks a step towards the development of distributed networks for quantum information processing.

Researchers have observed the inverse Doppler effect at optical frequencies, using a technique that combines a moving negative-index photonic crystal and heterodyne interferometry.

Alternative electrode materials and device geometries that avoid the use indium tin oxide — an expensive and brittle material widely used for making transparent electrodes in organic solar cells — are now coming to fruition.

Combining semiconductor quantum dots and atomic systems allows the light emitted from a quantum dot to be temporarily stored. Here, scientists describe a hybrid semiconductor-atomic interface that can slow down a single photon emitted from a quantum dot by 15 times its temporal width. The findings are attractive for the implementation of quantum memories and quantum repeaters.

Based on peristaltic nematogen microflows in polydimethylsiloxane, scientists demonstrate an optofluidic modulator that exhibits a symmetric 250 µs response and can operate at frequencies of up to 1 kHz.

Experimental investigation of the reverse-Doppler shift of electromagnetic waves has previously been restricted to the microwave regime. Here, direct confirmation of the Doppler effect is reported at the infrared wavelength of 10.6 µm using a moving photonic crystal exhibiting a negative refractive index.

Many X-ray imaging techniques require transmission geometries, which place severe restrictions on the samples being imaged. Here, a reflection geometry lensless X-ray imaging method is demonstrated. This technique may allow single-shot imaging of surfaces and films such as organic photovoltaic materials and field-effect transistor devices, or Bragg planes in a single crystal.

Single photons emitted from a quantum dot can be slowed down using a hybrid semiconductor–atomic interface. Nika Akopian from Delft University of Technology in The Netherlands explained to Nature Photonics how this non-classical light storage system works.

This focus issue brings together a collection of articles that describe the importance and latest progress of optical frequency combs, optical lattice clocks and quantum metrology, as well as techniques for measuring Casimir forces in complex microstructured geometries and ultrashort laser pulses — all of which are essential for realizing next-generation optical metrology.