Peter Tidemand-Lichtenberg

Efficient all solid-state continuous-wave yellow-orange light source

We present highly efficient sum-frequency generation between two CW IR lasers using periodically poled KTP. The system is based on the 1064 and 1342 nm laser-lines of two Nd:YVO4 lasers. This is an all solid-state light source in the yellow-orange spectral range. The system is optimized in terms of efficiency as well as stability. We compare the performance of a singly and a doubly resonant system, and find that the stability of the singly resonant system is superior to that of the doubly resonant system. We find that the overall conversion efficiency of the single resonant system is higher than for the doubly resonant configuration.

Red-IR stimulated luminescence in K-feldspar: Single or multiple trap origin?

We investigate on the origins of the infra-red stimulated luminescence (IRSL) signals in 3 potassium feldspars based on IR-red spectroscopy (∼700–1050 nm) using a fiber-coupled tunable Ti:Sapphire laser, in combination with different thermal and optical (pre)treatments of the samples. We also measure dose-response curves with different wavelengths and at different stimulation temperatures so as to be able to distinguish between traps based on their electron trapping cross-sections. Our data suggest that the dosimetric signals, IRSL, and the post IR-IRSL in K-feldspars arise from a single electron trapping centre.

Low-noise mid-IR upconversion detector for improved IR-degenerate four-wave mixing gas sensing.

We compare a nonlinear upconversion detector with a conventional cryogenic InSb detector for the detection of coherent infrared light showing near-shot-noise-limited performance in the upconversion system. The InSb detector is limited by dark noise, which results in a 500 times lower signal-to-noise ratio. The two detectors are compared for the detection of a coherent degenerate four-wave mixing (DFWM) signal in the mid-infrared, and applied to measure trace-level acetylene in a gas flow at atmospheric pressure, probing its fundamental rovibrational transitions. In addition to lower noise, the upconversion system provides image information of the signal, thus adding new functionality compared to standard point detection methods. We further show that the upconversion detector system can be implemented as a simple replacement of the cryogenic detector.

Tunable intra-cavity SHG of CW Ti:Sapphire lasers around 785 nm and 810 nm in BiBO-crystals

Phasematch curves as well as sensitivity to angular and wavelength misalignment for generation of second-harmonic of 785 nm and 810 nm in Bi(3)BO(6) crystal was calculated. Measurements were done for intra-cavity CW SHG in a Ti:Sapphire laser. The BiBO crystal was found to be excellent for this application. Temperature dependance was uncritical for both crystals, while power stability was good. Maximum blue output was 53 mW at 392 nm and 100 mW at 405 nm; corresponding to pump-to-blue optical conversion efficiencies of 0.96% and 1.82% respectively.

Efficient visible light generation by mixing of a solid-state laser and a tapered diode laser

A generic approach to efficient visible light generation based on singly-resonant sum-frequency mixing of an external-cavity tapered diode laser and a diode pumped solid-state laser is presented. The principle is exemplified by generation of more than 300 mW of 488 nm coherent blue light by mixing of a 950 mW beam from an external-cavity 765 nm tapered diode laser with the intra-cavity field of a diode pumped, high finesse 1342 nm solid-state laser using periodically poled KTP as the nonlinear medium. Using this approach, a conversion efficiency of more than 30 % of the 765 nm beam was obtained.

All passive synchronized Q-switching of a quasi-three-level and a four-level Nd:YAG laser

Using an all passive approach, synchronized Q-switching of two Nd:YAG lasers, at 946 nm and 1064 nm, is reported. Two laser crystals are used to avoid gain competition, and stable operation is reported for the first time. The pulse trains are synchronized over a wide range of pump powers and a relative timing jitter of 36 ns is achieved. A minimum delay of 64 ns is observed between the two laser pulses, and by making the 946 nm pulse relatively long, a 79% temporal overlap is obtained when compared to the zero-delay scenario.

First measurement of the nonlinear coefficient for Gd(1-X)Lu(X)Ca(4)O(BO(3))(3) and Gd(1-X)Sc(X)Ca(4)O(BO(3))(3) crystals.

The effective nonlinear coefficient and temperature acceptance bandwidth of three Lu and Sc co-doped GdCa(4)O(BO(3))(3) type nonlinear crystals were measured. NCPM for SHG in to the blue-UV spectral region can be obtained by controlling the co-dopant concentration. Measurements were based on intra-cavity SHG of a CW Ti:Sapphire laser, and the effective nonlinear coefficients were found to be in the range of 0.5 to 0.6 pm/V for the three crystals used. The FWHM temperature acceptance bandwidth was measured to be more than 35 degrees C using a 6 mm long Gd(0.871)Lu(0.129)Ca(4)O(BO(3))(3) crystal. A maximum of 115 mW at 407.3 nm in a single direction was measured using a 6.5 mm long Gd0.96Sc0.04Ca(4)O(BO(3))(3) crystal.

Upconversion imaging using an all-fiber supercontinuum source

In this Letter, the first demonstration, to the best of our knowledge, of pulsed upconversion imaging using supercontinuum light is presented. A mid-infrared (IR) imaging system was built by combining a mid-IR supercontinuum source emitting between 1.8 and 2.6 μm with upconversion detection. The infrared signal is used to probe a sample and mixed with a synchronized 1550 nm laser pulse inside a lithium niobate (LiNbO3) crystal. The signal is thus upconverted to the 860-970 nm range and acquired on a standard silicon CCD array at a rate of 22 frames per second. In our implementation, spatial features in the sample plane as small as 55 μm could be resolved.

Mid-infrared upconversion spectroscopy

Mid-infrared (MIR) spectroscopy is emerging as an attractive alternative to near-infrared or visible spectroscopy. MIR spectroscopy offers a unique possibility to probe the fundamental absorption bands of a large number of gases as well as the vibrational spectra of complex molecules. In this paper we discuss non-collinear upconversion as a means for obtaining MIR spectra in the 5–10 μm range with a resolution better than 20  cm−1 over the full interval using four discrete phase-match settings. A theoretical treatment of non-collinear upconversion is given and two different experimental implementations are tested.

Upconversion-based lidar measurements of atmospheric CO2

For the first time an upconversion based detection scheme is demonstrated for lidar measurements of atmospheric CO2-concentrations, with a hard target at a range of 3 km and atmospheric backscatter from a range of ~450 m. The pulsed signals at 1572 nm are upconverted to 635 nm, and detected by a photomultiplier tube, to test how the upconversion technology performs in a long range detection system. The upconversion approach is compared to an existing direct detection scheme using a near-IR detector with respect to signal-to-noise ratio and quantum efficiency. It is for the first time analyzed how the field-of-view of a receiver system, for long range detection, depends critically on the parameters for the nonlinear up-conversion process, and how to optimize these parameters in future systems.