Jae Yong Lee

Cavity ringdown spectroscopy with a continuous-wave laser: calculation of coupling efficiency and a new spectrometer design

For the efficient operation of a cavity ringdown spectroscopy (CRDS) system utilized with a continuous-wave (cw) laser, we numerically analyze the coupling efficiency of a cw laser to a ringdown cavity in terms of changes in the scanning rate, the laser linewidth, and the mirror reflectivity. We also demonstrate a new simple design for a CRDS system that can produce a CRDS signal with only a piezoelectric transducer (PZT), without the acousto-optic modulator that is usually adopted to switch off the cw laser beam that enters the cavity. Furthermore, we investigate the feasibility of the cw CRDS technique with a fast-scanning PZT by recording a CRDS spectrum of acetylene overtones. The detection sensitivity that corresponds to the noise-equivalent absorption is found to be approximately 3 x 10(-9)/cm.

Doubly resonant metallic nanostructure for high conversion efficiency of second harmonic generation

The recent discovery of strong nonlinear emission in metallic nanostructures has offered possibilities for realization of functional nano photonic devices. Here, we demonstrate a novel design of a plasmonic nano device for high conversion efficiency of second harmonic generation. A 4 × 4 bowtie aperture array is fabricated to have both plasmonic resonance for local field enhancement of the fundamental wave and Fabry-Pérot resonance for high transmission of second harmonic wave. Combining nano structures for exciting surface plasmon polariton and suppressing higher order diffraction and anti-reflection layer, we achieve a second harmonic conversion efficiency of 1.4 × 10(-8) that is nearly an order of magnitude larger than the results published in recent literatures. We also theoretically analyze evidences of the role of double resonances tuned to the fundamental wave and the second harmonic wave, resulting in the augmentation of second harmonic response approximately an order of magnitude greater than that without the help of the resonance.

Time Domain Study on Cavity Ring-Down Signals from a Fabry-Pérot Cavity under Pulsed Laser Excitations

We present an analysis on ring-down signals produced by a pulsed laser excitation of a Fabry-Perot cavity. Main features of a ring-down signal are numerically investigated by taking time domain approach under a simplistic assumption that a Fourier-transform-limited Gaussian laser pulse be injected to a stable empty cavity with complete mode-match to the lowest cavity transverse mode. Temporal aspects and output coupling efficiency of a ring-down signal are obtained with excitation pulse duration and cavity parameters taken into account. Clear physical insight is allowed in the time domain description especially for the forefront transient peak and the inherent intensity modulation which are found to be superimposed on a ring-down signal.

Uncertainty analysis of absolute concentration measurement with continuous-wave cavity ringdown spectroscopy

To evaluate the uncertainty of concentration measurement using cavity ringdown spectroscopy, we analytically derived expressions for uncertainty for parameters, such as temperature, laser frequency, and ringdown time deviation, from the model equation. The uncertainties that are due to systematic errors in a practical cavity ringdown system were assessed through an experimental study of the PQ(35) transition in an A band of molecular oxygen. We found that, except for the line strength that is regarded as a reference value independent of the measurement, the laser frequency jitter is the largest uncertainty source in the system. Some practical requirements for minimizing the uncertainty in concentration measurements are discussed. We also demonstrated determination of the line strength of the PQ(35) transition line of oxygen to be 8.63(3) x 10(-27) cm(-1) with a relative uncertainty of less than 0.4%.

Complex traversal time for optical pulse transmission in a Fabry–Perot cavity

We show that the physical clock approach can be applied to the problem of optical pulse transmission in the Fabry–Perot cavity. Our theoretical analysis leads directly to a complex-valued traversal time for the pulse. Real and imaginary parts of the traversal time, referred to as the phase time and the loss time, are associated, respectively, with the rotation angle of polarization and the change in the polarization ellipticity of the outgoing pulse in the presence of a magnetic clock. The physical significance of the phase time and the loss time is discussed in relation to the superluminal group velocity and the spectral shift of the pulse.

Measurement of ultralow supermirror birefringence by use of the polarimetric differential cavity ringdown technique

We demonstrate a novel technique for measuring ultralow linear birefringence of supermirrors (high-reflectivity dielectric mirror coatings). The polarimetric cavity ringdown technique is used in conjunction with the differential detection scheme with circular polarization to enhance the measurement sensitivity. The technique could, in principle, provide the convenience and reliability of linear detection signals and a reasonable tolerance to experimental imperfections. Phase retardation and orientation of each cavity mirror can be determined separately without the influence of the other mirror. The minimum detectable phase retardation achieved experimentally with this technique is ~6 x 10(-8) rad.

Experimental realization of a four-photon seven-qubit graph state for one-way quantum computation

We propose and demonstrate the scaling up of photonic graph states through path qubit fusion. Two path qubits from separate two-photon four-qubit states are fused to generate a two-dimensional seven-qubit graph state composed of polarization and path qubits. Genuine seven-qubit entanglement is verified by evaluating the witness operator. Six qubits from the graph state are used to demonstrate the Deutsch-Jozsa algorithm for general two-bit functions with a success probability greater than 90%.

Continuous-wave 532 nm pumped MgO:PPLN optical parametric oscillator with external power regulation and spatial mode filtering

We report a continuous-wave (CW) optical parametric oscillator (OPO) based on a MgO-doped periodically poled LiNbO(3) (MgO:PPLN) crystal. The 532 nm pump generates coherent radiation that is tunable from 800 to 920 nm for the signal and from 1250 to 1580 nm for the idler, respectively. The OPO output power exhibits a slowly varying instability that we attribute to a thermal effect induced by the pump. This instability is truncated by means of a low-pass servo that includes a single-mode fiber that filters the beam into a single spatial mode. The resulting output characteristics are promising for radiometric applications in the near infrared including most fiber-optic communication bands.

Spatiospectral transmission of a plane-mirror Fabry-Perot interferometer with nonuniform finite-size diffraction beam illuminations.

The transmission of a plane-mirror Fabry-Perot (PFP) interferometer is theoretically modeled and investigated by treating the spatial and spectral features in a unified manner. A spatiospectral transfer function is formulated and utilized to describe the beam propagation and the multiple-beam interference occurring in an ideal one-dimensional strip PFP interferometer with no diffraction loss. The spatial-frequency filtration of a finite-size beam input not only determines the transmitted spatial beam profile but also plays a crucial role in affecting the overall spectral transmittance. The inherent deviations of the spectral transmittance from what we know as the standard Airys formula are revealed in diverse aspects, including the less-than-unity peak transmittance, the displacement of a resonance peak frequency, and the asymmetric detuning profile. Our theoretical analysis extends to the misaligned PFP interferometers, such as the cases in which non-normal-incidence beams or wedge-aligned mirrors are used that could severely degrade the effective interferometer finesse.

Spatial-domain cavity ringdown from a high-finesse plane Fabry–Perot cavity

We investigate the optical transmission of a tilted plane Fabry–Perot cavity leading to spatial cavity ringdown, the exponentially decaying intensity output present along the transverse spatial coordinate. Primary features of the spatial cavity ringdown are theoretically predicted from the spectral and spatial cavity transfer function which is derived analytically on the combined basis of ray optics and diffraction theory applied to an ideal diffraction lossless cavity of one transverse dimension. Spatial frequency filtration by a narrow Lorentzian-shaped cavity resonance is shown to play key roles on the spatial aspects of transmitted beam profiles. Our theoretical formulation is further extended to the case of wedged plane Fabry–Perot cavities. The experimental observation of spatial cavity ringdown signals exhibits an excellent agreement with the theoretical prediction.