Hans P. Jenssen

Review of the properties of up-conversion phosphors for new emissive displays

In this paper, we review the properties of up-conversion (UC) materials and assess their potential for a new display technology. UC materials absorb near infrared light and re-emit in the visible. Some of their most appealing characteristics for displays are: a wide color gamut with very saturated colors, very high brightness operation without damage to the emitters, long lifetimes and efficiencies comparable to those of existing technologies. Other advantages include simplicity of fabrication, versatility of operation modes, and the potential for greatly reduced display weight and depth.

14-fs pulse generation in Kerr-lens mode-locked prismless Cr:LiSGaF and Cr:LiSAF lasers: observation of pulse self-frequency shift

Kerr-lens mode-locked Kr-laser-pumped Cr:LiSGaF and Cr:LiSAF lasers containing only two newly developed low-loss chirped mirrors instead of conventional dielectric resonator mirrors and generating pulses of widths as small as 14-fs with as much as 100 mW of average output power are reported. We report what is to our knowledge the first experimental observation of a pulse self-frequency shift in crystalline active media that are characteristic of such short pulses at megawatt intracavity peak powers. We also believe this phenomenon to be one of the significant limiting factors for pulse duration in femtosecond Cr:LiSAF-type lasers.

High-brightness white-light source based on up-conversion phosphors

We report the implementation of a new, high brightness, high efficiency white-light source based on up-conversion phosphors. Up-conversion materials absorb near infrared light and re-emit in red, green, and blue. It is possible to combine these colors to create a white-light source. Such a source has the same appealing characteristics as those reported for up-conversion displays: very high brightness operation without damage to the emitters, long lifetimes, and efficiencies comparable to those of existing technologies. In addition, they offer simplicity of fabrication and a variety of operating modes. Here we demonstrate a 7-lm/W D65 white light emitter yielding 2 kcd/m 2 on a simple diffuser

Temperature-dependent stimulated emission cross section in Nd 3+ :YVO 4 crystals

Spectroscopic properties of neodymium-doped yttrium orthovanadate crystals were measured in the temperature range between 5 and 350 K. Crystals fabricated by different suppliers, with 0.3 and 1 at% Nd3+, were compared. For each temperature, the stimulated emission cross sections of the Nd3+ 4F3/2 decay to the 4I9/2, 4I11/2, and 4I13/2 states were obtained using the Fuchtbauer-Ladenburg and the reciprocity techniques. Nd:YVO4 shows higher absorption at room temperature and higher stimulated emission cross section with similar variation with temperature when compared with Nd:YAG. The anomalous dependence on temperature of the Nd3+ 4F3/2 excited-state lifetime is discussed and an explanation is suggested.

Investigation of diode-pumped 2.8-µm laser performance in Er:BaY2F8

Laser operation at 2.8 mm in BaY2F8 with erbium concentrations of 7.5% and 20% is investigated under laser-diode pumping at 967 nm. Output powers as high as 250 mW and slope efficiencies as high as 24% are obtained. Results are comparable with those of Er3+:LiYF4 under the same pump conditions. Slope efficiencies above 30% are predicted for optimized erbium concentrations.

Investigation of diode-pumped 2.8-{bold {mu}}m laser performance in Er:BaY{sub 2}F{sub 8}

Laser operation at 2.8 mm in BaY2F8 with erbium concentrations of 7.5% and 20% is investigated under laser-diode pumping at 967 nm. Output powers as high as 250 mW and slope efficiencies as high as 24% are obtained. Results are comparable with those of Er3+:LiYF4 under the same pump conditions. Slope efficiencies above 30% are predicted for optimized erbium concentrations.

Kerr-lens mode-locked diode-pumped Cr:LiSGAF laser.

We have demonstrated stable and self-sustaining Kerr-lens mode locking of a Cr:LiSGAF laser pumped by AlGaInP laser diodes. A hard aperture near one end of the laser provides the necessary amplitude modulation. This allsolid- state system generates transform-limited 100-fs pulses, tunable from 810 to 860 nm. The average power at 830 nm is 35 mW, with fluctuations of much less than 1%. The thermal properties of Cr:LiSGAF will permit scaling of these results to higher power.

Fluorescence quantum efficiency measurements in the presence of Auger upconversion by the thermal lens method

Mode-mismatched thermal lens (TL) measurements in Cr3+-doped fluoride crystals (LiSrAIF6 and LiSrGaF6) are reported. A nonlinear increase of the TL signal, and decrease of quantum efficiency, with increasing excitation power was observed and attributed to energy-transfer upconversion (ETU). Assuming an upconversion rate that is proportional to the excited-state population, Wup = gammaN(e), the theoretical model developed fits the experimental data well. The ETU parameters (gamma) were determined with unprecedented accuracy for low Cr concentrations. Thermo-optical parameters (K, ds/dT) were also obtained.

EFFICIENT CONTINUOUS-WAVE TEM00 AND FEMTOSECOND KERR-LENS MODE-LOCKED CR:LISRGAF LASER

Efficient high-power (900-mW) TEM(00) cw operation of a Cr:LiSrGaF laser pumped by a Kr(+) laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr(+)-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Properties of a new, efficient, blue-emitting material for applications in upconversion displays: Yb, Tm:KY3F10.

The properties of Yb, Tm:KY3F1o, a cubic fluoride crystal, are described that make it attractive as the blue emitter in two-dimensional photonic displays. Its peak excitation wavelength for blue upconversion emission is 974.7 nm, where efficient diode laser pump sources are available. The maximum upconversion efficiency measured thus far is 4.4%.