Ultrasensitive detections in atomic and molecular physics: demonstration in molecular overtone spectroscopy

We consider several highly sensitive techniques commonly used in detection of atomic and molecular absorptions. Their basic operating principles and corresponding performances are summarized and compared. We then present our latest results on the ultrasensitive detection of molecular overtone transitions to illustrate the principle and application of the cavity-enhanced frequency-modulation (FM) spectroscopy. An external cavity is used to enhance the molecular response to the light field, and an FM technique is applied for shot-noise-limited signal recovery. A perfect match between the FM sideband frequency and the cavity free spectral range makes the detection process insensitive to the laser-frequency noise relative to the cavity, and, at the same time, overcomes the cavity bandwidth limit. Working with a 1.064-µm Nd:YAG laser, we obtained sub-Doppler overtone resonances of C2HD, C2H2, and CO2 molecules. A detection sensitivity of 5 x 10^-13 of integrated absorption (1 x 10^-14/cm) over 1-s averaging time has been achieved

Mounting system for optical frequency reference cavities

A technique for reducing the vibration sensitivity of laser-stabilizing optical reference cavities is based upon an improved design and mounting method for the cavity, wherein the cavity is mounted vertically. It is suspended at one plane, around the spacer cylinder, equidistant from the mirror ends of the cavity. The suspension element is a collar of an extremely low thermal expansion coefficient material, which surrounds the spacer cylinder and contacts it uniformly. Once the collar has been properly located, it is cemented in place so that the spacer cylinder is uniformly supported and does not have to be squeezed at all. The collar also includes a number of cavities partially bored into its lower flat surface, around the axial bore. These cavities are support points, into which mounting base pins will be inserted. Hence the collar is supported at a minimum of three points

Simple and Compact 1-Hz Laser System via an Improved Mounting Configuration of a Reference Cavity

We report an improved mounting configuration for a passive optical cavity used for laser frequency stabilization. The associated reduction of the vibration sensitivity of the effective cavity length has led to a simple and compact reference cavity system for laser stabilization at the level of 1 Hz linewidt

Cooperative three- and four- player quantum games

A cooperative multi-player quantum game played by 3 and 4 players has been studied. Quantum superposed operator is introduced in this work which solves the non-zero sum difficulty in previous treatment. The role of quantum entanglement of the initial state is discussed in details.Comment: 7 pages with 3 figures. To appear in Physics Letters

Simple and Compact Hz-Level Linewidth Laser System via Improved Mounting Configuration of a Reference Cavity

We report a simple, robust 1-Hz linewidth laser system enabled by an improved mounting strategy for optical reference cavities used for laser frequency stabilization

Optical Frequency Measurement across a 104-Thz Gap with a Femtosecond Laser Frequency Comb

The frequency-domain mode comb of a Ti:sapphire femtosecond laser centered at 350 THz is broadened to 150 THz (full width at −30 dBc) by self-phase modulation in a single-mode optical fiber. By phase locking continuous-wave lasers to elements of the comb near 1064 and 778 nm, we measure the 104-THz frequency gap between these two lasers with a relative uncertainty of 2.7×10−11 in 1 s

Measurement of Mirror Birefringence at the Sub-Ppm Level: Proposed Application to a Test of QED

We present detailed considerations on the achievable sensitivity in the measurement of birefringence using a high finesse optical cavity, emphasizing techniques based on frequency metrology. Alternative approaches of laser locking and cavity measurement techniques are discussed and demonstrated. High-precision measurements of the cavity mirror birefringence have led to the interesting observations of photorefractive activities on mirror surfaces

High-Resolution Frequency Standard at 1030 nm For Yb:YAG Solid-State Lasers

A diode-pumped solid-state Yb:YAG laser has been stabilized to a high-finesse cavity with an all-external servo loop. Ultrasensitive cavity-enhanced frequency modulation spectroscopy has recovered a sub-Doppler acetylene overtone transition with a high signal-to-noise ratio, leading to an absorption sensitivity of 7&times;10&minus;11 at a 1-s averaging time. This high-resolution molecular resonance serves as a long-term stable reference for the laser. The system can be developed into a highly compact and stable optical frequency standard in the 1.03-&micro;m wavelength range.</p