Generation of light of second harmonic frequency in a Gaussian light

J. Heinze, H. Vahlbruch, B. Willke

For future generations of gravitational wave detectors, it is proposed to use the helical Laguerre–Gaussian L G 3 , 3 mode to reduce thermal noise, which limits the detector sensitivity. At the same time, this requires the efficient generation of squeezed vacuum states in the L G 3 , 3 mode for quantum noise reduction. Since this technique includes the process of second harmonic generation (SHG), we experimentally compare the conversion efficiency and harmonic output field of the L G 0 , 0 and L G 3 , 3 modes in a cavity-enhanced SHG using the same 7% doped M g O : L i N b O 3 crystal. Conversion efficiencies of 96% and 45% are achieved, respectively. The influence of mode mismatches and astigmatism is analyzed to estimate the ratio of the pump mode-dependent effective nonlinearities to be d 0 , 0 / d 3 , 3 ∼ 5 . Furthermore, we show that absorption loss in the crystal is more relevant for the L G 3 , 3 mode.

B. Echtermeyer

ARTUR K. EKERT, Kazimierz Rza̧żewski

D. Yeaton-Massey, R. X. Adhikari

We report a bound on the relative frequency fluctuations in nonlinear second harmonic generation. A 1,064 nm Nd:YAG laser is used to read out the phase of a Mach-Zehnder interferometer while PPKTP, a nonlinear crystal, is placed in each arm to generate second harmonic light. By comparing the arm length difference of the Mach Zehnder as read out by the fundamental 1064 nm light, and its second harmonic at 532 nm, we can bound the excess frequency noise introduced in the harmonic generation process. We report an amplitude spectral density of frequency noise with total RMS frequency deviation of 3 mHz and a minimum value of 20 μHz/Hz½ over 250 seconds with a measurement bandwidth of 128 Hz, corresponding to an Allan deviation of 10⁻¹⁹ at 20 seconds.

Pavel Chmela

Andreas Sizmann, R. J. Horowicz, G Wagner +1 more

The most efficient sources of squeezed light have employed χ(2) processes in parametric downconversion or upconversion. In second harmonic generation both the fundamental and second harmonic modes are in an amplitude squeezed state. The upconverted mode is the squeezed state with the shortest wavelength involved in the process; therefore, frequency doubling is a promising scheme with which squeezing can be pushed toward the blue end of the spectrum. We measured the amplitude and phase noise properties of the second harmonic light generated in a frequency doubling monolithic cavity.