Cavity Second Harmonic Generation Research Articles

SECOND HARMONIC GENERATION USING A NON BIREFRINGENT MATERIAL IN A DOUBLY RESONANT MONOLITHIC CAVITY

Doubly resonant second harmonic generation (SHG) in a monolithic cavity is theoretically analysed. Using a non birefringent material as non linear medium, it is shown that both the double resonance condition and the phase matching condition between the two counter propagating second harmonic intracavity waves can be satisfied with a cavity length equal to the coherence length of the non linear process, and with well designed mirror phases. It is also shown theoretically how the double resonance can be maintained with only one tuning parameter. A SHG cavity enhancement of a few tens of thousands may be achieved at double resonance.

Active versus passive squeezing by second-harmonic generation

The characteristics of squeezed light generated by both passive (occurring in a cavity external to a laser) and active (occurring within a laser cavity) second-harmonic generation (SHG) are investigated and contrasted. Squeezing of both the fundamental and the second harmonic is discussed, and the issue of doubly versus singly resonant behavior is addressed. We examine passive squeezing by explicitly modeling the intrinsically noisy output of the pump laser and coupling it to a passive, multiport, lossy SHG cavity. Low-frequency degradation of the squeezing caused by the laser pump noise is predicted and provides a probable explanation for previous discrepancies between theory and experiment. Active squeezing is quantitatively modeled by a three-level laser model that retains all laser dynamics. Previously disparate predictions are reconciled. For one parameter set two regimes of squeezing are predicted: 50% squeezing at frequencies lower than the laser relaxation oscillation, and near-perfect squeezing at frequencies above. A particular problem of active squeezing is highlighted: The fast dephasing of the laser coherence introduces considerable excess noise likely to mask squeezing in experimental situations. We conclude that, although passive SHG is a practical source of squeezing, active SHG is unlikely to be so in the foreseeable future.

SURFACE EMITTED HARMONIC GENERATION FOR SENSOR AND DISPLAY APPLICATIONS

We review briefly some of the basic principles involved in quasi-phase matched multilayer semiconductor films for second-harmonic generation in waveguided, reflection and intra-cavity geometries. New applications in optical ranging for length, temperature, deformation sensors, real time optical reflectometry and vertical cavity second-harmonic generation for displays are presented. The enhancement of quasi-phase matched second-harmonic generation in vertical cavity Fabry-Perot structures is also investigated. When the optimal quasi-phase matching conditions are satisfied in the Fabry-Perot core, the second-harmonic conversion efficiency of a 4 μm thick cavity is enhanced by 1.75 × 106 relative to a homogeneous GaAs slab. This geometry is most suitable for intracavity harmonic generation in vertical cavity surface emitting lasers.

Handedness and mortality risk in older women : J. R. Cerhan, A. R. Folsom, J. D. Potter and R. J. Prineas, American Journal of Epidemiology, 140(4), 368–374

We experimentally demonstrate the second harmonic generation (SHG) of infrared femtosecond pulses using a BIBO crystal placed in an external ring cavity, synchronized with an input mode-locked laser at 78 MHz. A frequency doubling efficiency of 53% is achieved which is, to the best of our knowledge, the highest value ever reported for a low energy input beam of 1.4 nJ/pulse. Theoretical analysis of cavity related issues such as design, fundamental mode characteristics and fidelity against misalignments are also presented. The modeling of SHG cavity enables us to estimate the cavity losses and the mode matching visibility. Such synchronized SHG cavities in pulse domain, having higher SHG conversion efficiencies compared to their continuous wave counterparts, may find potential applications in scientific areas such as in photonics, and in quantum optics.

69% Efficient continuous-wave second-harmonic generation in lithium-rich lithium niobate

Lithium-rich lithium niobate fabricated by vapor transport equilibration is used to frequency double the output of an injection-locked Nd:YAG laser. Internal doubling efficiencies as high as 69% and powers of as much as 1.6 W are achieved by resonant external cavity second-harmonic generation. No evidence of photorefractive damage is observed at the operating temperature of 234 degrees C.

Nonlinear UV-laser spectroscopy of the 2 3S−5 3P transition in 3He and 4He

We report the production of stable CW single mode UV radiation around 295 nm at powers exceeding 50 mW, using a passive enhancement cavity for second harmonic generation. With this laser we have investigated the 2 3S−5 3P transition at 294.5 nm in 3He and 4He by intermodulated fluorescence spectroscopy. The measurements of the hyperfine splittings of the 5 3P levels agree with semi-empirical calculations.