Jerry C. Chen

Long-term femtosecond timing link stabilization using a single-crystal balanced cross correlator

We demonstrate a self-aligned balanced cross correlator based on a single type-II phase-matched periodically poled KTiOPO4 crystal. The birefringence of the crystal generates a walk-off between the two orthogonally polarized pulses. This enables the balancing of the cross correlator with input pulses at the same center wavelength. As a first application of this single-crystal balanced cross correlator, we stabilized a 310 m long optical fiber link for timing distribution with long-term stable 10 fs precision.

Optical detection of terahertz radiation by using nonlinear parametric upconversion

We describe and demonstrate sensitive room-temperature detection of terahertz (THz) radiation by nonlinearly upconverting terahertz to the near-infrared regime, relying on telecommications components. THz radiation at 700 GHz is mixed with pump light at 1550 nm in a bulk GaAs crystal to generate an idler wave at 1555.6 nm, which is separated and detected by using a commercial p-i-n diode. The THz detector operates at room temperature and has an intrinsic THz-to-optical photon conversion efficiency of 0.001%.

Optical detection of terahertz using nonlinear parametric upconversion

We extend our work to perform sensitive, room-temperature optical detection of terahertz (THz) by using nonlinear parametric upconversion. THz radiation at 700 GHz is mixed with pump light at 1,550 nm in a bulk GaAs crystal to generate an idler wave at 1,555.6 nm. The idler is separated, coupled into optical fiber, and detected using a gated Geiger-mode avalanche photodiode. The resulting THz detector has a power sensitivity of 4.5 pW/Hz and a timing resolution of 1 ns.

Terahertz Interferometer That Senses Vibrations Behind Barriers

A terahertz sensor that measures vibrations behind optically opaque barriers (cardboard, plastic, wool, cotton) is described and demonstrated. Using interferometric techniques, submicrometer displacements can be resolved. Measured spectral response agrees with commercial vibrometer

Phase Noise Characteristics of Fiber Lasers as Potential Ultra-Stable Master Oscillators

Fourth-generation light sources, such as the European X-Ray Free Electron Laser facility (XFEL), require timing signals distributed over distances of several kilometers with a timing jitter in the order of femtoseconds. The master clock for the proposed optical distribution system must operate with exceptionally low timing jitter. A promising approach is the use of a mode-locked laser that generates ultrastable pulses which are distributed via timing stabilized fiber links. Mode-locked Erbium-doped fiber lasers are attractive candidates, featuring very low noise at high frequencies. In this paper, we present a study of the phase noise of various mode-locked fiber lasers in view of their applicability as laser-based master oscillators for femtosecond-level timing distribution.

Ultrasensitive, Room Temperature Detection of THz Radiation Using Nonlinear Parametric Conversion

We demonstrate ultrasensitive, room temperature optical detection of terahertz by using nonlinear parametric upconversion. Terahertz radiation is mixed with pump light at 1550 nm in quasi-phase-matched GaAs crystal to generate an optical sideband or idler wave that is coupled into optical fiber and detected using a Geiger-mode APD. The resulting terahertz detector has a noise equivalent power of 78 fW/Hz1/2 with a timing resolution of 1 ns.

Ultra-sensitive, room-temperature THz detection based on parametric upconversion by using a pulsed 1550nm optical source

We demonstrate ultra-sensitive optical detection of terahertz by using nonlinear parametric upconversion. Terahertz radiation is mixed with pump light at 1550 nm in a nonlinear crystal to generate an optical sideband or idler wave. The idler signal is separated from the optical pump, coupled into an optical fiber and detected using a Geiger-mode avalanche photo-diode. Our scheme to detect THz waves leverages mature technology at 1550 nm developed for telecommunications to enable ultra-sensitive detection at room-temperature. We have fabricated a diffusion-bonded, quasi phasematched GaAs crystal, a χ(2) nonlinear material, that is pumped with a readily obtainable erbium doped fiber amplifier to perform the parametric conversion. We demonstrate efficient upconversion of terahertz radiation using both a continuous-wave THz source operating at 0.82 THz and a pulsed sub-picosecond THz source with spectral coverage from 0.5 THz to 1.5 THz. The resulting THz detector has a noise equivalent power of 78 fW/Hz1/2 with a timing resolution of 1 ns. χ(2) nonlinear interactions are intrinsically very fast; our temporal bandwidth is limited by the optical detector. Additionally, the THz detector demonstrates a broadband response with a phase-matching bandwidth exceeding 1 THz. This noise equivalent power of 78 fW/Hz1/2 and the corresponding power conversion efficiency of 1.2× 10-3 are the best reported, to our knowledge. This paper presents both theoretical and experimental results.

Terahertz generation and detection using nonlinear frequency conversion

Ti-sapphire is nonlinearly converted to 1 mW average terahertz power at 9.9% photon conversion efficiency. Terahertz is mixed with 1550 nm pump in quasi-phase-matched GaAs, for ultra-sensitive (78 fW/Hz1/2), room-temperature detection with nanosecond timing resolution.

Terahertz detection using optical parametric upconversion and geiger mode avalanche photodiodes

Terahertz radiation is nonlinearly upconverted to telecommunication wavelength. The resulting idler is coupled into fiber and detected with a photon counting receiver. Detection with 4.5 pW/Hz1/2 noise equivalent power and nanosecond temporal resolution is demonstrated.

Long-distance optical synchronization system for X-ray free electron lasers

Next generation light sources demand femtosecond-level synchronization of its subcomponents over distances of several km. We demonstrate an optical synchronization system based on distribution of mode-locked pulses over optical fiber in a real accelerator environment.