Abstract
The upconversion detection is a promising method to detect infrared radiation. It is proved that the focused beam makes a contribution to improving the upconversion efficiency. A near-infrared detector at room-temperature based on sum frequency generation(SFG) with focused beams is demonstrated. To enhance the upconversion efficiency, the signal and pump beams are tightly focused by the same focal lens. To reduce that the dispersion of the focal lens has a negative effect on upconversion efficiency in a tightly focusing system, the relation between the upconversion efficiency and the focused beams in our system is investigated. In the setup, the signal and pump beams are combined by a polarization maintaining wavelength division multiplexer (PMWDM) that is connected on a collimator. The mixed beam is focused into a periodically poled lithium niobate (PPLN) bulk by a lens of 35mm focal length. The signal pulse at 1550nm is converted to 863nm with a 172mW continuous-wave pump beam at 1950nm. The converted signal is measured by a photomultiplier tube(PMT) and results shows the maximum upconversion efficiency is 5.23×10-4 while the pump power is 172mW.
Highlights
N OWADAYS, the infrared(IR) detection technology plays an important role in remote sensing
To overcome that the upconversion efficiency suffers the limited pump power, we use a lens with short focal length focus the mixed beam into the periodically poled lithium niobate (PPLN)
Because the mixed beam that is output by a collimator connected with polarization maintaining wavelength division multiplexer (PMWDM) has a divergence within 0.075◦ with a diameter of 3.2mm, our system reaches maximum upconversion efficiency on condition that L1 and L2 are achromatic lenses with f = 35mm and ∆f = 0.29mm according to fig(8d)
Summary
N OWADAYS, the infrared(IR) detection technology plays an important role in remote sensing. It is hard to apply tightly focusing to enhance the upconversion efficiency because the dichroic mirror is placed between the lens and the nonlinear crystal. To overcome that the upconversion efficiency suffers the limited pump power, we use a lens with short focal length focus the mixed beam into the PPLN. Because the phase-mismatch and the interaction between the signal beam and the pump beam in PPLN are not independent on the dispersion, it is still necessary to investigate the influence of dispersion on the relation between the focused beams and the upconversion efficiency. To mix the signal pulse with the pump beam, a 1550nm pulse laser and a 1950nm continue-wave laser are connected with a polarization maintaining wavelength division multiplexer. With the effective area diameter of the PMT is 7mm, all the converted light can be detected
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