Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

Non-Critical Phase-Matched Second Harmonic Generation In GdXY1-XCob

We have characterized non-critical phase-matching (NCPM) for both Type I and Type II second harmonic generation (SHG) in y-cut GdxY1-xCOB using a nanosecond optical parametric oscillator (OPO). The variation of the NCPM wavelength with temperature was investigated for different values of the compositional parameter x. Efficient SHG of 1064 nm was achieved by choosing the suitable compositional parameter x = 0.28 and by tuning the temperature of the crystal to 52°C. Using a 25-mm-long Gd0.28Y0.72COB crystal, conversion efficiencies of 41 and 43% were obtained respectively from a mode-locked Nd : YAG and a Q-switched Nd : YAG laser

Spectral Shaping To Improve The Point Spread Function In Optical Coherence Tomography

We demonstrate inhibition of the sidelobes of the axial point spread function in optical coherence tomography by shaping the power spectrum of the light source with a remaining power of 4.54 mW. A broadband amplified spontaneous emission source radiating at 1565 ± 40 nm is employed in a free-space optical coherence tomography system. The axial point spread functions before and after optical spectral shaping are presented. Results show that spectral shaping of the source can inhibit sidelobes of the point spread function up to 12.9 dB, with an associated small increase of 2.2 dB in noise floor in the far field. The effect of spectral shaping on axial resolution is demonstrated according to three metrics. Image quality improvement is also illustrated with optical coherence tomography images of an onion before and after spectral shaping. © 2003 Optical Society of America

Laser action in Yb\u3csup\u3e3+\u3c/sup\u3e:YCOB (Yb\u3csup\u3e3+\u3c/sup\u3e:YCa4O(BO3)3)

Infrared laser action in Yb3+:YCOB (Yb3+:YCa4O(BO3)3) is reported for the first time. Maximum output powers of ∼ 300 mW with a slope efficiency of 35.8% have been obtained. The observation of self-frequency doubling in this material is also reported. © 1998 Elsevier Science B.V. All rights reserved

Diode pumped laser action and self-frequency doubling in Nd\u3csup\u3e3+\u3c/sup\u3e:YCOB

Development of the oxyborate materials has brought about the realization of single crystal elements under diode pumped operation for compact, simple, solid state lasers producing visible laser emission. YCOB doped with Nd3+ has the distinct advantage of combining both an active laser medium with a modest nonlinear coefficient without associated photorefractive damage and self-absorption as with other self-frequency doubling (SFD) lasers. By beam shaping high brightness diodes and proper mode matching of the cavity mode with the laser mode, SFD output powers as high as those achieved by Ti:sapphire pumping can be obtained. Laser action with slope efficiencies of 51% and have generated 62 mW of green light by SGD of the fundamental light is demonstrated

Laser Action In Yb\u3csup\u3e3+\u3c/sup\u3e:Ycob (Yb\u3csup\u3e3+\u3c/sup\u3e:Yca4O(Bo3)3)

Progress in the growth of the rare earth calcium oxyborate crystals has now generated a new class of laser materials that can be used as both a laser host and a nonlinear frequency converter. Laser action and self-frequency doubling (SFD) has been observed with both 10% and 20% Yb3+-doped YCOB crystals. Laser operation was obtained in a hemispherical linear cavity, end-pumped with a tunable cw Ti:Sapphire or a 980 nm laser diode pump source. Under Ti:Sapphire pumping at 900 nm, an output power of 230 mW and a slope efficiency of 29% was obtained using the 10% doped sample. Laser action was seen at 1050 nm. Laser operation of the 20% sample had a maximum output power of approximately 300 mW with a slope efficiency of 35.8% at 1088 nm. Laser action was not obtained at the peak of the fluorescence emission (approximately 1030 nm) in this crystal as a consequence of self-absorption on the short-wavelength side of the emission band. Diode-pumped operation at the narrow absorption peak of 977 nm was achieved and early results show an improved slope efficiency of 34% in comparison to the 10% doped crystal under Ti:Sapphire pumping. We have also observed self-frequency doubling in Yb3+:YCOB. The 20% Yb3+:YCOB crystal used for this test was cut with a phase-matching angle of 36.22°. The self-frequency doubling efficiency was low due to the absence of any frequency selective elements in the cavity to narrow the linewidth of the fundamental emission. The SFD emission occurred at 543 nm