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NASA NTRS2009

Distinguishing non-resonant four-wave-mixing noise in coherent stokes and anti-stokes Raman scattering

A method of examining a sample comprises exposing the sample to a pump pulse of electromagnetic radiation for a first period of time, exposing the sample to a stimulant pulse of electromagnetic radiation for a second period of time which overlaps in time with at least a portion of the first exposing, to produce a signal pulse of electromagnetic radiation for a third period of time, and interfering the signal pulse with a reference pulse of electromagnetic radiation, to determine which portions of the signal pulse were produced during the exposing of the sample to the stimulant pulse. The first and third periods of time are each greater than the second period of time.

Marks, Daniel L.↗

NASA NTRS1993

Self-pumped phase conjugation and four-wave mixing in 0- and 45-deg-cut n-type BaTiO3:Co

Relatively fast self-pumped phase-conjugate and four-wave-mixing rise times are reported in n-type cobalt-doped barium titanate. With the crystal oriented in a 45-deg cut as compared with the same crystal in a 0-deg cut we find a factor of 3 decrease in the 0-90-percent rise time to 800 ms with 25-mW input power at 514.5 nm. Also, the self-pumped phase-conjugate reflectivity increases from 20 to 40 percent. We deduce that the phase conjugation is from internally seeded stimulated photorefractive backscattering. The four-wave-mixing rise time of the 45-deg-cut crystal is 4 ms with a reflectivity of 48 percent when the pumping beams are derived from self-pumped phase conjugation that has an input power of 25 mW.

Garrett, M. H.↗

NASA NTRS1987

Four-mode squeezing

The four-wave-mixing interactions produced by pumping at two well-separated frequencies can couple four different radiation modes to generate a new kind of squeezed state of light. A dual-frequency homodyne detection scheme is described and is used to observe this type of nonclassical correlation. Initial experimental results in an optical fiber show a noise level 20 percent below the vacuum noise level for the output of the dual-frequency detector, even though the noise at each individual detector remains above the vacuum level.

Schumaker, B. L.↗

NASA NTRS1989

Optical Processing With Photorefractive Semiconductors

Experimental phase-conjugate four-wave-mixing apparatus used to demonstrate capabilities of GaAs (and potentially of other photorefractive semiconductors like InP and CdTe) for optical processing of information. With modifications, performs any of three basic image-processing functions: transfer to different light beam, enhancement of edges, and autocorrelation. Includes crystal of GaAs of 5 by 9 by 9 mm with cubic crystalline axes. Advantages include high speed and compatibilty with other semiconductor devices.

Cheng, Li-Jen↗

NASA NTRS1989

Optical Stark effect in the four-wave mixing and stimulated Raman spectra of N2

The influence of the optical Stark effect on spectral line shapes in four-wave-mixing Raman spectroscopy (FWMRS) and stimulated Raman spectroscopy (SRS) is investigated experimentally and theoretically. Using an experimental setup capable of rapid alternation between the simultaneous measurement of coherent Stokes Raman spectroscopy and inverse Raman spectroscopy at low and high intensities, together with a sophisticated frequency reference scheme, it was possible to perform a rather direct comparison between Stark-broadened and non-Stark-broadened spectra of both classes of Raman spectroscopies. The results demonstrate that SRS spectra show more Stark shift and broadening than their FWMRS counterparts. A discrepancy with theoretical results is pointed out, and an attempt is made to explain it.

Moosmuller, H.↗

NASA NTRS2004

Hyper-Parametric Oscillations in a Whispering Gallery Mode Fluorite Resonator

This viewgraph presentation summarizes the hyper-parametric oscillations observations of the fluorite resonator. The reporters have observed various nonlinear effects in ultra-high Q crystalline whispering gallery mode (WGM) resonators. In particular, it was demonstrated a low threshold optical hyper-parametric oscillations in a high-Q (Q=1010) CaF2 WGM resonator. The oscillations result from the resonantly enhanced four-wave-mixing occurring due to Kerr nonlinearity of the material.

four wave mixing↗

NASA NTRS2007

Raman-Suppressing Coupling for Optical Parametric Oscillator

A Raman-scattering-suppressing input/ output coupling scheme has been devised for a whispering-gallery-mode optical resonator that is used as a four-wave-mixing device to effect an all-optical parametric oscillator. Raman scattering is undesired in such a device because (1) it is a nonlinear process that competes with the desired nonlinear four-wave conversion process involved in optical parametric oscillation and (2) as such, it reduces the power of the desired oscillation and contributes to output noise. The essence of the present input/output coupling scheme is to reduce output loading of the desired resonator modes while increasing output loading of the undesired ones.

Savchenkov, Anatoliy↗