Z.D. Luo

2.0W diode-pumped Er:Yb:YAl3(BO3)4 laser at 1.5–1.6μm

An efficient and high output power laser has been realized for an Er:Yb:YAl3(BO3)4 crystal end pumped by a 970nm diode laser. Under the absorbed pump power of 15.5W, quasi-continuous-wave output power of 2.0W at 1.5–1.6μm has been obtained in a hemispherical cavity. The laser had an absorbed pump threshold power of 4.7W and a slope efficiency of 21%. The influence of the laser output power and output coupler transmission on the output laser spectra has also been investigated.

Improving the performance of a neodymium aluminium borate microchip laser crystal by resonant pumping

Laser action at 1.06μm from a neodymium aluminium borate microchip laser crystal has been demonstrated under F3∕24 direct excitation at 882nm. We have found that the laser slope efficiency increases from 50% up to 70% when resonant pumping is used instead of the traditional I9∕24→F5∕24(808nm) pumping. We conclude that the reduction in the pump-induced heat generation achieved by resonant pumping is at the origin of this improvement.

The evaluation of phasemeter prototype performance for the space gravitational waves detection.

Heterodyne laser interferometry is considered as the most promising readout scheme for future space gravitational wave detection missions, in which the gravitational wave signals disguise as small phase variances within the heterodyne beat note. This makes the phasemeter, which extracts the phase information from the beat note, the key device to this system. In this paper, a prototype of phasemeter based on digital phase-locked loop technology is developed, and the major noise sources which may contribute to the noise spectra density are analyzed in detail. Two experiments are also carried out to evaluate the performance of the phasemeter prototype. The results show that the sensitivity is achieved 2π μrad/√Hz in the frequency range of 0.04 Hz-10 Hz. Due to the effect of thermal drift, the noise obviously increases with the frequencies down to 0.1 mHz.

Methodological demonstration of laser beam pointing control for space gravitational wave detection missions

In space laser interferometer gravitational wave (G.W.) detection missions, the stability of the laser beam pointing direction has to be kept at 10 nrad/√Hz. Otherwise, the beam pointing jitter noise will dominate the noise budget and make the detection of G.W. impossible. Disturbed by the residue non-conservative forces, the fluctuation of the laser beam pointing direction could be a few μrad/√Hz at frequencies from 0.1 mHz to 10 Hz. Therefore, the laser beam pointing control system is an essential requirement for those space G.W. detection missions. An on-ground test of such beam pointing control system is performed, where the Differential Wave-front Sensing technique is used to sense the beams pointing jitter. An active controlled steering mirror is employed to adjust the beam pointing direction to compensate the jitter. The experimental result shows that the pointing control system can be used for very large dynamic range up to 5 μrad. At the interested frequencies of space G.W. detection missions, between 1 mHz and 1 Hz, beam pointing stability of 6 nrad/√Hz is achieved.

Site-selective excitation and emission of Eu 3+ -doped transparent glass ceramic containing Ca 5 (PO 4 ) 3 F nanocrystals

An Eu3+-doped transparent oxyfluoride glass ceramic containing Ca5(PO4)3F nanocrystals was prepared by melt quenching and subsequent thermal treatment. The transmittance of the glass ceramic with a thickness of 1.92 mm is up to 80.5% in the visible range at room temperature. Site-selective excitation and emission spectra indicate that Eu3+ ions in the Ca5(PO4)3F nanocrystals occupy two types of sites, A and B, with a same point symmetry Cs. As for Eu3+ ions at site A, the crystal field is more deformed and stronger. The crystal field may appear in the form of a ligand ion F- being replaced by O2- in accordance with the charge compensation scheme: Ca2+ + F-→Eu3+ + O2-. As for Eu3+ ions at site B, the possible charge compensation scheme is 3Ca2+→2Eu3+ + Vacancy. Furthermore, an energy transfer process from Eu3+ ions at site A to that at site B in the glass ceramic at low temperature was also discussed.

Effect of Ce 3+ doping on the spectroscopic properties and 1.55 μm laser operation of Er:Yb:Ce:NaY(WO 4 ) 2 crystal

Er:NaY(WO4)2 and Er:Yb:Ce:NaY(WO4)2 crystals were grown by the Czochralski method. Er:Yb:NaY(WO4)2, Er:Ce:NaY(WO4)2, and Yb:NaY(WO4)2 crystal powders were synthesized by means of the solid-state reaction. The spectroscopic properties of the crystals were investigated, including the absorption and fluorescence spectra and fluorescence decay. The energy transfer efficiency from Yb3+ to Er3+ in Er:Yb:NaY(WO4)2 and Er:Yb:Ce:NaY(WO4)2 was calculated and analyzed. End-pumped by a diode laser at 970 nm in a hemispherical cavity, a 1.84 W quasi-continuous-wave laser around 1.55 μm with a slope efficiency of 17% and an absorbed pump threshold of 1.60 W was achieved in a 1.04 mm thick c-cut Er:Yb:Ce:NaY(WO4)2 crystal. The results show that the Er:Yb:Ce:NaY(WO4)2 crystal with high Ce3+ doping is a candidate for gain medium of low threshold 1.55 μm laser.

Excited-state absorption in NdAl3(BO3)4 laser crystal

We present an investigation in NdAl3(BO3)4 (NAB) crystal of the excited-state absorption (ESA) around the main laser lines (1060 and 1338 nm) by the so called excited-state excitation technique. The involved transitions are from the 4F3/2 level toward the 4G7/2+4G9/2+2K13/2 levels (1300–1400 nm range) or toward the 2G9/2+4G11/2+2D3/2+2K15/2 levels (1020–1100 nm range). We have performed the Judd–Ofelt analysis extended to anisotropic crystals in order to get the cross sections (cm2). In each case, the ESA peaks do not coincide with the laser emission ones, but a reduction of the effective laser emission cross section is observed at 1338 nm. Finally, the values obtained from the application of the Judd–Ofelt formalism have been used to estimate the influence of ESA in the pumping domain on the laser performance. It has been found that its contribution is not significant, indicating that NAB is an excellent candidate for efficient high-power microchip lasers emitting at 1060 and 1338 nm.

Spectral properties and 1.5–1.6 μm laser operation of Er:Yb:NaCe(WO4)2 crystal

An Er:Yb:NaCe(WO4)2 crystal was grown by the Czochralski method. Spectral properties of the crystal were investigated and compared with those of the Er:Yb:Ce:NaGd(WO4)2 crystal. The green up-conversion was not observed when the Er:Yb:NaCe(WO4)2 crystal was excited by a diode laser at 970 nm. The efficiency of energy transfer from Yb3+ to Er3+ in the Er:Yb:NaCe(WO4)2 crystal was calculated to be about 93%. End-pumped by a diode laser at 970 nm in a hemispherical cavity, 0.95 W quasi-CW laser at 1.5–1.6 μm was achieved in a 1.47-mm-thick c-cut Er:Yb:NaCe(WO4){ia2} crystal, the slope efficiency was 11%, and the threshold was 2.83 W.

Single longitudinal mode laser oscillation from a neodymium aluminium borate stoichiometric crystal

We report on single mode 1.06μm laser oscillation from a 882nm pumped NdAl3(BO3)4 stoichiometric crystal. When operating in continuous wave regime, laser slope efficiencies in excess of 50% have been obtained from a 250μm thick cavity. Additionally, stable single mode nanosecond (2ns) and subnanosecond (200ps) pulses have been generated by Q-switching the microchip cavity with semiconductor saturable absorbed mirrors. In this way peak powers in excess of 500W have been obtained while keeping single mode oscillation.

Solid state laser source for simultaneous generation of green and red radiation

An all-solid-state simultaneous green and red laser source is demonstrated based on a diode-pumped Nd3+-doped crystal operating in the 4F3/2?4I13/2 laser channel. Coherent green radiation was achieved by sum frequency mixing of pump (800?nm) and fundamental (1.3??m) radiation inside an intracavity KTP crystal. At the same time, laser radiation in the red was obtained by second harmonic generation of infrared (IR) radiation in an additional intracavity KTP crystal. We have tested this scheme by using both YAG and YVO host crystals for the Nd3+ ions. The influence of IR multiline oscillation on the spectral and spatial characteristics of visible radiation is discussed.