Cavity-enhanced sum-frequency generation of blue light with near-unity conversion efficiency

Abstract

We report on double-resonant highly efficient sum-frequency generation in the blue range. The system consists of a 10-mm-long periodically poled KTP crystal placed in a double-resonant bowtie cavity and pumped by a fiber laser at 1064.5 nm and a Ti:sapphire laser at 849.2 nm. An optical power of 375 mW at 472.4 nm in a TEM00 mode was generated with pump powers of 250 mW at 849.2 nm and 200 mW at 1064.5 nm coupled into the double-resonant ring resonator with 88% mode-matching. The resulting internal conversion efficiency of 95(±3)% of the photons mode-matched to the cavity constitutes, to the best of our knowledge, the highest overall achieved quantum conversion efficiency using continuous-wave pumping. Very high conversion efficiency is rendered possible due to very low intracavity loss on the level of 0.3% and high nonlinear conversion coefficient up to 0.045(0.015) W −1 . Power stability measurements performed over one hour show a stability of 0.8%. The generated blue light can be tuned within 5 nm around the center wavelength of 472.4 nm, limited by the phase-matching of our nonlinear crystal. This can however be expanded to cover the entire blue spectrum (420 nm to 510 nm) by proper choice of nonlinear crystals and pump lasers. Our experimental results agree very well with analytical and numerical simulations taking into account cavity impedance matching and depletion of the pump fields.

Quantum frequency conversion of vacuum squeezed light to bright tunable blue squeezed light

“…This stabilization technique locks the Ti:sapphire laser frequency to the DR SFG cavity, and thus to the 1064-nm laser, ensuring a high frequency stability of the SFG output field. More details about the SFG cavity and the theoretical analysis can be found in our recent published work on double-resonant highly efficient SFG [15]. In Fig.…”

“…For example, it has been demonstrated that a squeezed vacuum can be converted from the NIR at 1550 nm to the green region at 532 nm through sum-frequency generation (SFG) driven by a strong coherent pump at 810 nm [13]. We present the experimental realization of a QFC system based on highly efficient SFG in a double resonant cavity [14][15], where a tunable pump beam at 850 nm ±50 nm and a vacuum squeezed seed beam at 1064 nm are mixed using a periodically poled (PP)KTP nonlinear crystal to produce wavelength-tunable bright squeezed light in the blue spectral region, see Fig. 1 for the principle outline of the experiment and the cascaded nonlinear interactions.…”

Quantum frequency conversion of vacuum squeezed light to bright tunable blue squeezed light and higher-order spatial modes

“…The cavity has an FSR of 767(±4) MHz, a finesse of 88(±5), and thus a cavity bandwidth of 8.7(±0.5) MHz. More details about the SFG cavity and the theoretical analysis can be found in our recent published work on double-resonant highly efficient SFG [34]. In Fig.…”

“…We find that the theoretical model is an very good agreement with the measured squeezing spectrum taking into account transfer functions of the SFG cavity and phase fluctuations. The generated SFG beam is in a diffraction limited TEM 00 mode with M 2 ¡ 1.05 [34]. The high spatial-mode quality of the SFG output is readily provided by the DR cavity design and makes our SFG system potentially useful as a light source for various types of microscopes, high spatial resolution scatterometry, and dark-field wafer inspection.…”

“…For example, it has been demonstrated that a squeezed vacuum can be converted from the NIR at 1550 nm to the green region at 532 nm through sum-frequency generation (SFG) driven by a strong coherent pump at 810 nm [19,31]. By this principle, SFG enables the production of squeezed quantum states of light in the complete ultraviolet to visible range by using the coherent pump laser for wavelength selectivity -ultimately realizing a source of tunable squeezed-light at wavelengths that are otherwise difficult to access [14,16,18,19,[32][33][34].…”