G. Aka

Diode-pumped Yb:Sr(3)Y(BO(3))(3) femtosecond laser.

We have developed a diode-pumped Yb(3+)Sr(3)Y(BO(3))(3) (Yb:BOYS) laser generating 69-fs pulses, at a central wavelength of 1062 nm. This laser is mode locked by use of a semiconductor saturable-absorber mirror and emits 80 mW of average power at 113 MHz. This is, to our knowledge, the first mode-locked Yb:BOYS laser and the shortest duration obtained from an ytterbium laser with a crystalline host. The central wavelength can be tuned from 1051 to 1070 nm, for sub-100-fs pulses. We have also achieved an average power as high as 300 mW with pulse duration of 86 fs at 1068 nm.

Ytterbium-doped Ca 4 GdO(BO 3 ) 3 : an efficient infrared laser and self-frequency doubling crystal

The surge of interest in ytterbium-doped materials has led to their being proposed as substitutes for their widely used neodymium counterparts for infrared laser emission. Spectroscopic and laser investigations of ytterbium-doped Ca4GdO(BO3)3 (Yb:GdCOB), a new ytterbium-doped crystal, are reported. Laser performances under titanium:sapphire pumping suggest that this material is suitable for schemes that include laser-diode pumping. A maximum slope efficiency of 58.8% with a corresponding laser threshold of 40 mW has been demonstrated with a 1% output coupler. Laser oscillations were also observed for output-coupler transmissions of as much as 10%. Self-frequency doubling of infrared-laser emission has been observed for the first time to our knowledge in an ytterbium-doped medium. The recent demonstration of the interesting self-frequency-doubling properties of neodymium-doped Ca4GdO(BO3)3 suggests that Yb:GdCOB could also be efficient in visible laser emission because of its lack of reabsorption at the second-harmonic wavelength. All these results show that the calcium oxoborate family can be useful compact and efficient laser-diode-pumped visible-laser sources.

Generation of 90-fs pulses from a mode-locked diode-pumped Yb 3+ :Ca 4 GdO(BO 3 ) 3 laser

A diode-pumped Yb>(3+):Ca(4)GdO(BO>(3))(3) (Yb:GdCOB) laser generating 90-fs pulses at a center wavelength of 1045 nm is demonstrated. This is, to our knowledge, the shortest pulse duration obtained from an ytterbium laser with a crystalline host. This laser is mode locked with a high-finesse semiconductor saturable-absorber mirror and emits 40 mW of average power at a repetition rate of 100 MHz.

Spectroscopic properties and laser performances of Yb:YCOB and potential of the Yb:LaCOB material

Abstract In order to increase the compacity of the Yb-doped lasers, YCOB (Ca 4 Y(BO 3 ) 3 ) materials with high ytterbium concentration have been characterized. Large 15 at.% and 35 at.% ytterbium-doped single crystals were grown by the Czochralski pulling method. Spectroscopic and laser properties have been investigated and laser tests performed under titanium sapphire and diode pumping at 976 nm. Low thresholds under Ti:Sa pumping (50 mW) and high slope efficiency under diode pumping (66%) have been obtained. The optical quality and the distribution of Yb 3+ dopant through the highly doped crystals is discussed. First results on the Yb:LaCOB crystals grown by the Czochralski process, containing 46Yb 3+ at.%, are also presented.

Structural and thermal stability of Czochralski grown GdCOB oxoborate single crystals

Properties such as chemical and structural stability, thermal expansion and thermal conductivity are investigated, with the purpose of better characterizing the behaviour of Czochralski grown GdCOB [Ca4GdO(BO3)3], oxoborate single crystals, to be used in optical devices.

Optical and laser properties of Yb:Y2SiO5 single crystals and discussion of the figure of merit relevant to compare ytterbium-doped laser materials

Abstract In this paper, we explore two different directions in the investigation of Yb-doped solid-state laser crystals. At first, we describe the spectroscopic properties, site occupancies, energy-level diagrams and laser performances of Yb:Y2SiO5 (Yb:YSO), a new promising laser material. Then, in a more general point of view, we discuss the problem of evaluating the laser potential of the known Yb-based lasers. The approach proposed by De Loach et al. [IEEE J. Quantum Electron. 29 (1993) 1179] is shown to be incomplete to some extent. In a search for new figures of merit, it seems reasonable to include other parameters such as the thermal properties of the host.

Quasi-three-level 946 nm CW laser emission of Nd:YAG under direct pumping at 885 nm into the emitting level

Abstract The possibility to enhance the laser emission characteristics and to reduce the heat generation for the 946 nm Nd:YAG laser by direct pumping into the emitting level is discussed. Improved laser characteristics are demonstrated with a 1 at.% Nd:YAG component under 885 nm pumping into the thermally activated transitions Z2→R1 and Z3→R2 of the 4 I 9/2 → 4 F 3/2 absorption.

Overview of the laser and non-linear optical properties of calcium-gadolinium-oxo-borate Ca4GdO(BO3)3

Abstract Ca 4 GdO(BO 3 ) 3 (GdCOB) is a new non-linear optical (NLO) material which presents a congruent melting and can be grown from the melt in large size crystals ( φ =50 mm, L =120 mm) using the Czochralski pulling method. This paper describes the crystal growth and NLO properties of GdCOB which compare favorably with those of commercial borates like BBO or LBO. Particular emphasis will be put on SHG of the Nd:YAG 1.064 μm laser emission. Large amounts of Nd or Yb ions can be substituted for Gd in this material and Ln:GdCOB with Ln=Nd, Yb exhibits interesting laser properties, especially in the case of diode pumped Yb activated crystals. Finally by combining the NLO properties of the GdCOB matrix and the laser emission associated with the active ion, a green self frequency-doubling laser is obtained. In this field, Nd:GdCOB appears the most promising material for practical applications, able to generate visible green laser light with only one single crystal instead of two, as usually. To date an Nd:GdCOB crystal yields 114 mW at 530.5 nm (for 1250 mW of absorbed pump power), when pumped with a 2 W high brightness laser diode.

Nd :GdCOB: overview of its infrared, green and blue laser performances

Abstract GdCOB (Ca4GdB3O10) is a new non-linear optical material which can be grown in large sized crystals by the Czochralski method. In this material, part of the gadolinium ions can be replace by Nd3+ without significant decrease of the crystal quality. Nd:GdCOB single crystals exhibit laser action in the infrared at 1060 and 1091 nm simultaneously. The two transitions involved originating from the two Kramers doublets of the 4F3/2 state, their respective contributions depend upon the temperature of the Nd:GdCOB crystal. By combining the non-linear properties of the GdCOB matrix and the laser emission due to ND3+ ions, it is possible to generate directly by self-frequency doubling 115 mW of green laser light at 530.5 nm under diode pumping at 810 nm. It is also possible to self-double the 936 nm emission of Nd:GdCOB, leading to blue laser emission, but only under pulsed titanium-sapphire laser pumping. However, a CW blue laser beam is obtained in Nd:GdCOB by self sum-frequency mixing of the 1090 nm laser emission and the residual pump beam at ∼812 nm, yielding 1.2 mW of 465 nm laser light, with an optical to optical efficiency of 0.3%. This paper ends with a survey of the Nd:YCOB laser characteristics which are compared to those of Nd:GdCOB.

Nonlinear optical properties of Ca 5 (BO 3 ) 3 F crystal

A high quality Ca5(BO3)3F (CBF) crystal, grown by flux method, was investigated for its non linear optical properties. This material is non hygroscopic and possesses a moderate birefringence suitable for UV light generation. On the basis of its refractive index dispersion curves, it is inferred that CBF has great potential applications as non linear optical material, notably for UV light generation at 355 and 266nm. In order to characterize its non linear optical properties, CBF samples were first cut and oriented in phase matching conditions for second harmonic generation of 1064nm. Experimental results demonstrate that CBF has the moderate NLO coefficients. The optical conversion efficiency from 1064nm to 532nm was investigated for the first time: up to 54% were achieved. Non linear deff coefficients were also estimated as well as the external angular acceptance bandwidth of SHG at 1064nm.