Lawrence L. Tankersley

Time-gated imaging through dense scatterers with a Raman amplifier

A time-gated Raman amplifier has been used to detect a bar chart hidden by a strongly scattering material. The time gating was provided by a frequency-doubled Nd:YAG pump laser having a pulse duration of 30 ps. We have amplified and detected images with resolved structures smaller than 125 µm through suspensions of polystyrene spheres and nondairy creamer for light extinction factors of up to e(33). The Raman amplifier system has been shown to produce images under conditions in which the scattering medium was sufficiently dense that an image could not be detected on either a streak camera or by integration on a sensitive, low-noise camera.

Low-light-level, quantum-noise-limited amplification in a stimulated Raman amplifier

We have investigated the noise characteristics and the low-light-level imaging capabilities of a stimulated Raman amplifier. Diffraction-limited Stokes beams as well as Stokes beams carrying spatial structure have been amplified with a collimated pump with a Fresnel number in the range 3–17. Both direct imaging and Fourier-transform imaging of the Stokes signal through the Raman amplifier were used. Results indicate that approximately 1–4 photons per spatial mode are needed to produce images with a signal-to-noise ratio of 1. Amplification of the Fourier transform of the object effectively provides spatial filtering of the noise and gives the best signal-to-noise ratio at the lowest input levels for our experiments.

Chromatic time lag in picosecond streak camera measurements.

Ihlemann et al. [Rev. Sci. Instrum. 59, 2502 (1988)] have found unexpectedly large group velocity dispersion produced by commercial picosecond streak camera objective lenses. Our work supports and extends their lens data.