Dual function of Nd<sup>3+</sup> in Nd,Er:LuYSGG crystal for LD pumped ~3.0 &#x03BC;m mid-infrared laser

Yan Wang; Jianfu Li; Zhaojie Zhu; Zhenyu You; Jinlong Xu; Chaoyang Tu

doi:10.1364/OE.23.018554

1. Introduction

In recent years, solid state lasers operating around ~3.0 μm based on the ⁴I_11/2→⁴I_13/2 transition of Er³⁺ have attracted much attention, due to their wide utilization in many fields, such as laser surgery, dentistry, remote sensing etc [1–3]. Moreover, ~3.0 μm laser is also attractive as a pump source for a far-infrared waveband optical parametric oscillation (OPO) or optical parametric generation (OPG) laser system, which have broad applications in spectroscopy, radar, atmospheric detection and defense etc [4, 5].

Even so, there are still mainly two challenging obstacles to prevent the improvement and development of Er³⁺-activated ~3.0 µm lasers: one is the low absorption efficiency of laser diode (LD) pumping energy for Er³⁺ doped laser crystals, which are usually pumped by commercial 980 or 800 nm LDs, owing to the weak intensity and narrow bandwidth of the intrinsic absorption bands of Er³⁺ with peaks around 980 or 800 nm corresponding to ⁴I_11/2→⁴I_15/2 or ⁴I_9/2→⁴I_15/2, respectively. In order to solve this problem, Yb³⁺ or Nd³⁺ ions with strong and broad absorption bands around 980 nm or 808 nm have usually been introduced as the sensitizer to improve the absorption [6–8]. The other main obstacle preventing the development of Er³⁺-doped laser is the self-terminating “bottleneck” effect, which results from the much shorter lifetime of the laser upper level ⁴I_11/2 than the lower level ⁴I_13/2, and thus might cause the ~3.0 μm laser to terminate owing to the populations in upper level unable to transform to the lower level quickly. To overcome this negative effect, one solution is to reduce the lifetime of the lower level ⁴I_13/2 of Er³⁺ by co-doping with depopulation ions such as Nd³⁺ [8], Pr³⁺ [9], Ho³⁺ [10–12], Eu³⁺ [11,12] or Tm³⁺ [12] etc. These ions can decrease the lower-level populations effectively, and thus lower ~3.0 µm laser threshold and increase laser output power. Therefore, interests in studying the spectroscopy of the depopulation ions co-doped, Er³⁺-activated laser crystals and ~3.0 µm solid-state lasers have increased recently [2,3,6–12]. Among all the rare earth ions, Nd³⁺ is the only one able to act as sensitization and depopulation ions simultaneously, therefore, we chose Nd³⁺ as the co-dopant ions in Er³⁺ activated bulk laser crystal in this work.

To date, most of the researches of erbium ~3.0 µm lasers have focused on garnet crystal hosts due to their outstanding physicochemical, optical and laser properties [2,3,6,10,12–20], such as Y₃Al₅O₁₂ (YAG), Gd₃Ga₅O₁₂ (GGG), Y₃Sc₂Ga₃O₁₂ (YSGG), GSGG (Gd₃Sc₂Ga₃O₁₂) etc., among which Er:YSGG/YSGG composite crystal has achieved the highest laser output power and efficiency [15]. YSGG crystal belongs to cubic system and Ia3d space group, with the same garnet structure as famous and commercial YAG crystal. The mean ion radius of Sc, Ga is 0.696 Å and the lattice parameter is 12.4584 Å [21]. Its density is 5.643 g/cm³ and the melting point is 1877°C [21]. As it melts congruently, large size single crystals can be obtained by the Czochralski (CZ) method. Compared with YAG crystal, YSGG crystals has lower phonon energy which could result in the decrement of the nonradiative transition ratio between the two energy levels (⁴I_11/2 and ⁴I_13/2) of Er³⁺ ions, and thus decrease the laser threshold and improve the laser output power and efficiency [17,21]. Recently, a new hybrid crystal with formula Er:GYSGG (Gd_1.17Y_1.83Sc₂Ga₃O₁₂) was invented which has superior optical and laser properties than Er:YSGG [2,10,14]. Owing to the big gap of the radius between Gd³⁺ (93.8 pm) and Y³⁺ (88 pm), it might be difficult for GYSGG crystal to accept high concentration Er³⁺ (88.1 pm), while the radius of Lu³⁺ (84.8 pm) is smaller than that of Gd³⁺ and more close to Y³⁺, we think there will possibly be an effect of compensation when Lu³⁺ was co-doped into the YSGG crystal [22], therefore, we design a new hybrid crystal written as Lu_0.15Y_2.85Sc₂Ga₃O₁₂ (abbr. as LuYSGG below) by substituting a fraction of Y³⁺ ions with Lu³⁺ ions in the YSGG crystal, and in Nd,Er:LuYSGG crystal three ions Nd³⁺, Er³⁺ and Lu³⁺ ions have the chance to enter the dodecahedral site of Y³⁺, which makes the crystal structure more complex and more disordered. As a result, the emission bands of Er³⁺ in the Nd,Er:LuYSGG crystal might be broadened dramatically as compared with that in Er:YSGG crystal, and the newly mixed Nd,Er:LuYSGG crystal might be suitable for Q-switching and mode-locking operation because of its broader fluorescence line width. Due to Nd³⁺/Er³⁺ multi-center distribution and the more complex structure of host material, we believe that Nd,Er:LuYSGG crystal could possess wider inhomogeneously broadened spectra, which would be suitable for mode-locking operation. However, the growth of mixed single crystal Nd,Er:LuYSGG has not yet been reported up till now.

The choice of dopant concentrations of Er³⁺ and Nd³⁺ in LuYSGG crystal is based on theoretical analyses and our previous serial work [3,6,8,12]: in theory, the high concentration of Er³⁺ doped systems (at least≥10at%) can help to improve the absorption intensity and line width of Er³⁺ and thus increase the pumping energy, also, it can help to suppress the self-saturation problem since high concentration Er ions are proposed to induce upconversion from ⁴I_11/2 and ⁴I_13/2, as well as cross-relaxation from ⁴S_3∕2, and thus aids the establishment of a continuous-wave gain at ~3.0 µm in Er³⁺ activated crystals [10]; as for Nd³⁺, its doping concentration shouldn’t be too high (at least ≤5at%), in order to prevent a sharp decrease of the fluorescence lifetimes of laser upper and lower levels of Er³⁺ and restrain strong infrared waveband emissions. From another perspective, the doping of too high concentration of rare earth ions might make it difficult to obtain high-optical-quality crystal and usually decrease its thermal conductivity. In our previous work [8], the concentrations of Nd³⁺ and Er³⁺ in SrGdGa₃O₇ crystal were chosen to be 5 at% and 30 at% respectively, but we found that the grown crystal had some scatter particles, and the fluoresence lifetime of Er³⁺:⁴I_11/2 level was extremely short (0.164 ms), hence afftected the output of the target 2.5~3µm laser, therefore, the choice of dopant ions’ concentrations should be reasonable based on the consideration of every possible problems. In this job, we have synthetized a serial of different concentration Nd³⁺ and Er³⁺ codoped Nd,Er:LuYSGG polycrystalline powders and measured their absorption, fluorescence spectra and fluorescence decay curves carefully, after a careful comparison of their optical properties, finally the concentration of Nd³⁺ is adjusted to be 5 at% and Er³⁺ to be 20 at% in the title crystal host.

In this work, we have grown the Nd³⁺ and Er³⁺ codoped LuYSGG crystal successfully for the first time by using Czochralski (CZ) method. Its absorption spectra, near-infrared and mid-infrared fluorescence spectra as well as the fluorescence decay curves were measured at room temperature. The ~3.0 μm emission properties and the energy transfer mechanism of Nd,Er:LuYSGG crystal were discussed. Nd³⁺ was demonstrated to greatly facilitate the Er³⁺:⁴I_11/2→⁴I_13/2 ~3.0 μm emission by efficient mutual energy transfers between Nd³⁺ and Er³⁺ ions. The spectroscopy investigation of ~3.0 μm emission has been made for potential high power laser output in practical operation.

2. Experimental details

The 5 at% Nd³⁺ and 20 at% Er³⁺-codoped LuYSGG single crystal was grown by the CZ technique, 20 at% Er³⁺ singly doped YSGG crystal was also grown for spectral comparison. 99.99% purity Y₂O₃, Ga₂O₃, Sc₂O₃ and 99.999% purity Lu₂O₃, Er₂O₃ and Nd₂O₃ commercial powders (Haipuri Rare Earth Materials Company, China) were dried and then weighed out according to the compositional formula, with an extra 1wt% Ga₂O₃ to compensate Ga loss owing to its evaporation. The mixtures were ground, mixed and pressed into tablets, then heated up in a Muffle furnace till 1200 °C at the rate of 100°C/h, and maintaining at this temperature for 48h to react completely. Then the tablets were taken out and the calcined powders were milled and pressed into tablets again, sintered at 1450°C for 18 h. The above procedures were repeated twice to confirm the finally synthesized polycrystalline compounds by using X-ray diffraction (Dmax2500, Rigaku) method. The crystals were grown with <111> direction YSGG seeds and carried out in DJL-400 furnace (NCIREO, China) with rotation speed of 12.0~20.0 rpm, pulling rate of 1.0~3.0 mm/h and annealing rate of 8.0~30.0 °C/h, finally two good optical quality crystals were obtained for the next spectral measurements.

The concentrations of Nd³⁺, Er³⁺, Lu³⁺, Y³⁺, Sc³⁺ and Ga³⁺ in the grown crystals were measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) analysis.

Two samples in random direction were cut from the as-grown Nd,Er:LuYSGG and Er:YSGG crystals with dimensions of 5.0 × 5.0 × 1.0 mm³, respectively. The two 5.0 × 5.0 mm² faces were polished for spectral experiments. Absorption spectra of Nd,Er:LuYSGG and Er:YSGG crystals were measured by Perkin-Elmer UV-Vis-NIR Spectrometer (Lambda-900). The near-infrared (NIR) wavelength fluorescence spectra and decay curves were recorded in Edinburgh Instruments FLS920 spectrophotometer, by using 808 LD pump source. The mid-infrared (MIR) fluorescence spectra and decay curves were recorded by Edinburgh Instruments FSP920 spectrophotometer, under 808 nm pumping with a 5 ns pulse of an optical parametric oscillator. All the measurements were carried out at room temperature (RT), and the two samples were measured under the exactly same experimental conditions.

3. Results and discussion

The doping concentrations of Nd³⁺ and Er³⁺ in doubly-doped LuYSGG crystal were measured to be 3.51 × 10²⁰ and 2.24 × 10²¹ ions⋅cm⁻³, respectively. The doping concentration of Er³⁺ in singly-doped YSGG crystal was measured to be 2.21 × 10²¹ ions⋅cm⁻³. According to the effective segregation coefficient equation k_eff = c₁/c₂, where c₁ and c₂ are the respective concentrations of the ions in the crystal and raw materials, k_eff values of Nd³⁺ and Er³⁺ in Nd,Er:LuYSGG crystal were determined to be 0.58 and 0.98, respectively, and k_eff value of Er³⁺ in Er:YSGG crystal were determined to be 0.93. Figure 1 shows the XRD pattern of the Nd,Er:LuYSGG crystal powder, and it is well consistent with the standard JCPDF file [No.25-1246] for YSGG crystal, which means that there is no phase transformation even after Lu³⁺, Nd³⁺ and high concentration Er³⁺ are doped into YSGG crystal.

Fig. 1 The XRD pattern of Nd,Er:LuYSGG single crystal.

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Absorption spectra of Nd,Er:LuYSGG and Er:YSGG crystals are shown in Fig. 2. As seen in Er:YSGG crystal, ten characteristic absorption bands of Er³⁺ centered at the wavelengths of 377, 407, 451, 488, 524, 542, 654, 790, 967, 1469 (1533) nm have been revealed, which are assigned to the transitions from the ground state (⁴I_15/2) to ⁴G_11/2, ²H_9/2, ⁴F_5/2 + ⁴F_3/2, ⁴F_7/2, ²H_11/2, ⁴S_3/2, ⁴F_9/2, ⁴I_9/2, ⁴I_11/2 and ⁴I_13/2, respectively. While in Nd,Er:LuYSGG crystal, besides the characteristic absorption bands of Er³⁺, we also observe the absorption bands of Nd³⁺: the main peaks centered at 364, 570, 589, 748, 808, 878 nm are assigned to the transitions from Nd³⁺: ⁴I_9/2 to ⁴D_3/2, ⁴G_7/2 + ⁴G_9/2, ⁴G_5/2 + ²G_7/2, ⁴F_7/2 + ⁴S_3/2, ⁴F_5/2 + ²H_9/2 and ⁴F_3/2, respectively.

Fig. 2 Absorption spectra of Nd,Er:LuYSGG and Er:YSGG crystals at RT.

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The absorption cross-section $σ_{a}$ can be determined by the following equation [3]:

σ_{a} = \frac{α}{N_{c}} = \frac{A}{N_{c} L \times \lg e} .

Here α is the absorption coefficient, A is the absorbance, L is the thickness of the polished sample, and N_c is the dopant ions concentration in the crystal. Thereby, the absorption cross-section of Nd,Er:LuYSGG with peak at 808 nm is calculated to be 5.25 × 10⁻²⁰ cm², meanwhile, the absorption cross-section of Er:YSGG with peak at 790 nm is calculated to be 1.56 × 10⁻²¹ cm², and the full width at half maximum (FWHM) of them are 8 nm and 3 nm, respectively. The absorption cross section of Nd,Er:LuYSGG crystal is more than 33 times of Er:YSGG crystal.

Apparently, the Nd³⁺/Er³⁺ co-doped crystal exhibits much more intense and wider absorption than that of Er³⁺ doped crystal at around 808 nm, thus indicating that Nd³⁺/Er³⁺ co-doped sample can absorb the pump energy of 808 nm more effectively, which makes it very suitable for AlGaAs laser diode pumping. The absorption at around 808 nm in the co-doped sample involves both the contributions from Er³⁺ and Nd³⁺ ions owing to the transitions Er³⁺:⁴I_15/2→⁴I_9/2 and Nd³⁺: ⁴I_9/2→⁴F_5/2 + ²H_9/2, respectively. Owing to the small energy gap between Nd³⁺:⁴F_5/2 + ²H_9/2 (approximately 12500 cm⁻¹) and Er³⁺:⁴I_11/2 (approximately 10000 cm⁻¹), it is expected that efficient resonance energy transfer could occur from Nd³⁺ to Er³⁺ and thus improve the MIR emission greatly.

Figure 3 shows the 850~1700 nm wavelength near-infrared (NIR) emission spectra of Er:YSGG and Nd,Er:LuYSGG crystals under 808 nm excitation. The weak emission around 1002 nm and the much strong emission around 1534 nm were observed in Er:YSGG crystal due to the transition of Er³⁺:⁴I_11/2→⁴I_15/2 and Er³⁺:⁴I_13/2→⁴I_15/2, respectively. However, as seen in Nd,Er:LuYSGG crystal, 1.5-μm emission is quenched obviously as compared with the Er³⁺ single doped sample, and the strongest emissions with peaks at 1061 and 1104 nm are caused by Nd³⁺, corresponding to ⁴F_3/2→⁴I_11/2. Also, we can observe the other several peaks at round 882 (936) and 1335 nm, which are caused by Nd³⁺ ions too, corresponding to ⁴F_3/2→⁴I_9/2 and ⁴F_3/2→⁴I_13/2, respectively. The 1.5-μm emission quenching phenomenon indicates that the depopulation of Er³⁺:⁴I_13/2 level by Nd³⁺ in Nd,Er:LuYSGG crystal is very effective, and thus beneficial to the ~3.0 μm emission in Er³⁺ activated LuYSGG crystal.

Fig. 3 NIR emission spectra of Er:YSGG and Nd,Er:LuYSGG crystals excited by 808 nm.

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The MIR emission spectra of Er:YSGG and Nd,Er:LuYSGG crystals pumped by 808 nm and measured under the same experimental conditions are presented in Fig. 4. The observed strongest emission bands around 2640 and 2820 nm are assigned to Er³⁺:⁴I_11/2→⁴I_13/2 in both crystals. It is found that more intense emission is detected in Nd, Er:LuYSGG crystal than in Er:YSGG crystal, and the introduction of Nd³⁺ ions enhance the emission intensity by nearly 2.2 times.

Fig. 4 MIR emission spectra of Er: YSGG and Nd, Er: LuYSGG crystals under 808 nm pumping.

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In order to explain the above-mentioned absorption and emission spectra, the energy level diagram of Nd³⁺ and Er³⁺ is presented in Fig. 5. The possible mechanisms of the energy transfer processes between Nd³⁺ and Er³⁺ ions were explained as follows: in Er:YSGG, Er³⁺ ions are excited by 808 nm photons from ground state ⁴I_15/2 to ⁴I_9/2 state, then relaxed to ⁴I_11/2 and ⁴I_13/2 levels, and thus ~1.5 µm emission (⁴I_13/2→⁴I_15/2) and ~3.0 μm emission (⁴I_11/2→⁴I_13/2) can be observed as seen in Fig. 3 and Fig. 4, respectively. The weaker intensity of ~3.0 μm emission in Er:YSGG crystal indicates that nonradiative transition is the main route for depopulating ⁴I_11/2. However, once Nd³⁺ ions are introduced into Er³⁺ activated LuYSGG crystal, the 808 nm pump energy is mainly absorbed by Nd³⁺ via the transition ⁴I_9/2→⁴F_5/2 + ²H_9/2. On one hand, a part of the excited Nd³⁺ ions at ⁴F_5/2 + ²H_9/2 relax nonradiatively to ⁴F_3/2 and give a well-known emission with peak at 1061 nm corresponding to ⁴F_3/2→⁴I_11/2 transition as seen in Fig. 3. On the other hand, Nd³⁺ ions in the ⁴F_5/2, ²H_9/2 and ⁴F_3/2 levels transferred their energy to Er³⁺:⁴I_9/2 and ⁴I_11/2 via the processes:

Fig. 5 The energy level diagram of Nd³⁺ and Er³⁺ ions for Nd,Er:LuYSGG crystal.

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\begin{array}{l} ({Nd}^{3 +} :^{4} F_{5 / 2},^{2} H_{9 / 2} + {Er}^{3 +} :^{4} I_{15 / 2}) \to ({Nd}^{3 +} :^{4} I_{9 / 2} + {Er}^{3 +} :^{4} I_{9 / 2}), \\ ({Nd}^{3 +} :^{4} F_{5 / 2},^{2} H_{9 / 2} + {Er}^{3 +} :^{4} I_{15 / 2}) \to ({Nd}^{3 +} :^{4} I_{9 / 2} + {Er}^{3 +} :^{4} I_{11 / 2}), \\ and ({Nd}^{3 +} :^{4} F_{3 / 2} + {Er}^{3 +} :^{4} I_{15 / 2}) \to ({Nd}^{3 +} :^{4} I_{9 / 2} + {Er}^{3 +} :^{4} I_{11 / 2}) . \end{array}

These energy transfer processes (named as ET1) from Nd³⁺ to Er³⁺ increased the population of Er³⁺:⁴I_11/2, which led to enhanced ~3.0 μm emission corresponding to ⁴I_11/2→⁴I_13/2 as observed in Fig. 4. Meanwhile, an obvious quench phenomenon was observed in the 1.5- μm emission as shown in Fig. 3 in Nd,Er:LuYSGG crystal, which is due to the presence of energy transfer channel ET2, that is (Er³⁺:⁴I_13/2, Nd³⁺:⁴I_9/2)→(Er³⁺:⁴I_15/2, Nd³⁺:⁴I_15/2). The introduction of Nd³⁺ depopulates ⁴I_13/2 level of Er³⁺, which is helpful to the population inversion for ~3.0 μm laser operation.

To further explore the energy interaction mechanism, the fluorescence decay curves of Er³⁺:⁴I_13/2 and ⁴I_11/2 multiplets of Er:YSGG and Nd,Er:LuYSGG crystals were measured at 1534 and 2640 nm excited by 808 nm, respectively, as shown in Fig. 6. And the decay curves from the ⁴I_13/2 and ⁴I_11/2 levels of Er:YSGG crystal both show singly-exponential decay behavior, while the decay curve from Er³⁺:⁴I_11/2 level of Nd,Er:LuYSGG crystal is doubly-exponential decaying. The fluorescence lifetimes were fitted and presented in Fig. 6. It is noticed that the fluorescence lifetime of ⁴I_11/2 state (0.57 ms) is shorter than that of ⁴I_13/2 state (2.06 ms) in Er:YSGG crystal. As we pointed previously, the shorter lifetime of laser upper level ⁴I_11/2 than lower level ⁴I_13/2 will make the accumulated population in the ⁴I_11/2 levels unable to relax quickly enough to maintain the necessary population inversion, and then cause the ~3.0 µm lasing transition to self-terminate automatically. In this work, the codopant Nd³⁺ quenched the emission corresponding to ⁴I_13/2→⁴I_15/2 and decreased the lifetime of ⁴I_11/2 state from 0.57 to 0.38 ms, thus suppressed the self-termination bottleneck effect successfully.

Fig. 6 Fluorescence decay curves of Er³⁺:⁴I_11/2, ⁴I_13/2 and Nd³⁺:⁴F_3/2 levels in Nd,Er:LuYSGG and Er:YSGG crystals.

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The energy transfer efficiency of Nd³⁺→Er³⁺ via ET1 in Nd,Er:LuYSGG crystal can be estimated by the following equation [23]:

η_{T} = 1 - \frac{τ_{N d - E r}}{τ_{N d}} .

Where

τ_{N d - E r}

is the lifetime of Nd³⁺:⁴F_3/2 of Nd,Er:LuYSGG crystal,

τ_{N d}

is the lifetime of Nd³⁺:⁴F_3/2 of Nd:YSGG crystal with same Nd³⁺ concentration as in Nd,Er:LuYSGG crystal. The fluorescence decay curve of the Nd³⁺:⁴F_3/2 multiplets of Nd,Er:LuYSGG crystal was measured at 1061 nm excited by 808 nm, as shown in Fig. 6 too. By linear fitting, the fluorescence lifetime is fitted to be 20.26 µs, which is much shorter than that of Nd:YSGG crystal (240 µs) [21]. Therefore, the energy transfer efficiency of Nd³⁺→Er³⁺ via ET1 is calculated to be 91.6%. Similarly, the energy transfer efficiency of Er³⁺→Nd³⁺ via ET2 in Nd,Er:LuYSGG crystal can be estimated. Since the 1.5 µm emission of Er³⁺ is quenched in Nd Er:LuYSGG crystal, we can think the energy transfer efficiency via ET2 is close to 100%.

The emission cross sections are calculated by the F-L equation [14]:

σ_{e m} (λ) = \frac{β λ^{5}}{8 π c n^{2} τ_{r}} \frac{I (λ)}{\int λ I (λ) d λ} .

Where

I (λ) / \int λ I (λ) d λ

is the normalized line shape function of the experimental emission spectrum, β is the fluorescence branching ratio, c is the speed of light, n is the refractive index and τ_r is the radiative lifetime. The maximum emission cross section of Nd,Er:LuYSGG crystal is estimated to be 1.84 × 10⁻¹⁹ cm² at 2640 nm, which is larger than that of Er:YSGG crystal (1.02 × 10⁻¹⁹ cm²), ascribing to the shorter radiative lifetime and higher fluorescence branching ratio of the ⁴I_11/2→⁴I_13/2 transition for the Nd,Er:LuYSGG crystal.

Herein, we list the spectral properties of several erbium activated garnet crystals in Table 1. As seen in these data, the absorption cross-section and emission cross-section of Nd, Er: LuYSGG crystal are much bigger than the other similar crystals.

Table 1. The spectral parameters of several erbium activated garnet crystals

View Table

4. Conclusions

The spectroscopic properties of Nd,Er:LuYSGG crystal were studied systematically. Compared with Er:YSGG crystal, the ~1.5 µm emission is quenched in Nd,Er:LuYSGG crystal, meanwhile, the intensity of the target ~3.0 μm emission enhances 2.2 times owing to the presence of Nd³⁺ ions. Furthermore, the lifetimes of the Er³⁺:⁴I_11/2 upper laser level fall from 0.57 ms to 0.38 ms, and that of ⁴I_13/2 level decreases sharply from 2.06 ms to quenching, which indicating that the self-saturation effect for the Er³⁺ ~3.0 μm laser is effectively suppressed. The energy transfer efficiency of Nd³⁺→Er³⁺ (ET1) in Nd,Er:LuYSGG crystal is estimated to be 91.6%, and that of Er³⁺→Nd³⁺ (ET2) is almost 100%. These results indicate that Nd³⁺ codoping is beneficial in achieving ~3.0 μm laser in Nd,Er:LuYSGG crystal, and this crystal can be acted as an excellent candidate for MIR lasers.

Acknowledgments

This work is supported by National Nature Science Foundation of China (51472240, 91122033 and 11304313), Knowledge Innovation Program of Chinese Academy of Sciences (KJCX2-EW-H03), Key Laboratory of Functional Crystal Materials and Device (No. JG1403, Shandong University, Ministry of Education), State Key Laboratory of Rare Earth Resource Utilization (No. RERU2015018, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences), Science and Technology Plan Cooperation Project of Fujian Province (2015I0007) and Nature Science Foundation of Fujian Province (2015J05134).

References and links

1. I. T. Sorokina, “Solid-State mid-infrared laser sources,” Top. Appl. Phys. 89, 255–351 (2013).

2. J. Chen, D. Sun, J. Luo, H. Zhang, S. Cao, J. Xiao, H. Kang, Q. Zhang, and S. Yin, “Performances of a diode end-pumped GYSGG/Er,Pr:GYSGG composite laser crystal operated at 2.79 μm,” Opt. Express 22(20), 23795–23800 (2014). [CrossRef] [PubMed]

3. Y. Wang, Z. You, J. Li, Z. Zhu, E. Ma, and C. Tu, “Spectroscopic investigations of highly doped Er³⁺:GGG and Er³⁺/Pr³⁺:GGG crystals,” J. Phys. D Appl. Phys. 42(21), 215406 (2009). [CrossRef]

4. K. L. Vodopyanov, “Mid-infrared optical parametric generator with extra-wide (3~19μm) tunability: applications for spectroscopy of two-dimensional electrons in quantum wells,” J. Opt. Soc. Am. B 16(9), 1579–1586 (1999). [CrossRef]

5. I. T. Sorokina and K. L. Vodopyanov, “Pulsed Mid-IR Optical Parametric Oscillators,” in Solid-State Mid-Infrared Laser Sources, 2nd ed., vol. 4 (Springer, 2003).

6. Y. Wang, Z. You, J. Li, Z. Zhu, and C. Tu, “Spectroscopic analyses of Yb,Er:Gd₃Ga₅O₁₂ crystal as a novel candidate of LD pumped ~3.0 μm laser,” Mater. Res. Bull. 48(8), 2969–2972 (2013). [CrossRef]

7. X. Zhuang, H. Xia, H. Hu, J. Hu, P. Wang, J. Peng, Y. Zhang, H. Jiang, and B. Chen, “Enhanced emission of 2.7 µm from Er³⁺/Nd³⁺-codoped LiYF₄ single crystals,” Mater. Sci. Eng. B 178(5), 326–329 (2013). [CrossRef]

8. Y. Wang, J. Li, Z. You, Z. Zhu, J. Xu, and C. Tu, “Enhanced 2.7 μm emission and its origin in Nd3+/Er3+ codoped SrGdGa3O7 crystal,” J. Quant. Spectrosc. Radiat. Transf. 149, 253–257 (2014). [CrossRef]

9. Z. Zhu, J. Li, Z. You, Y. Wang, S. Lv, E. Ma, J. Xu, H. Wang, and C. Tu, “Benefit of Pr3+ ions to the spectral properties of Pr3+/Er3+:CaGdAlO4 crystal for a 2.7 μm laser,” Opt. Lett. 37(23), 4838–4840 (2012). [CrossRef] [PubMed]

10. J. Chen, D. Sun, J. Luo, J. Xiao, H. Kang, H. Zhang, M. Cheng, Q. Zhang, and S. Yin, “Spectroscopic, diode-pumped laser properties and gamma irradiation effect on Yb, Er, Ho:GYSGG crystals,” Opt. Lett. 38(8), 1218–1220 (2013). [CrossRef] [PubMed]

11. S. Lv, Z. Zhu, Y. Wang, Z. You, J. Li, and C. Tu, “Spectroscopic investigations of Ho³⁺/Er³⁺:CaYAlO₄ and Eu³⁺/Er³⁺:CaYAlO₄ crystal for 2.7 μm emission,” J. Lumin. 144, 117–121 (2013). [CrossRef]

12. Y. Wang, Z. You, J. Li, Z. Zhu, E. Ma, and C. Tu, “Spectroscopic characterization of single crystals Cr,Er,Re:GGG (Re=Tm,Ho,Eu) as ~3.0 µm laser materials,” J. Lumin. 132, 693–696 (2012). [CrossRef]

13. D. Sun, J. Luo, J. Xiao, Q. Zhang, J. Chen, W. Liu, H. Kang, and S. Yin, “Luminescence and thermal properties of Er:GSGG and Yb,Er:GSGG laser crystals,” Chin. Phys. Lett. 29(5), 054209 (2012). [CrossRef]

14. J. Chen, D. Sun, J. Luo, H. Zhang, R. Dou, J. Xiao, Q. Zhang, and S. Yin, “Spectroscopic properties and diode end-pumped 2.79 μm laser performance of Er,Pr:GYSGG crystal,” Opt. Express 21(20), 23425–23432 (2013). [CrossRef] [PubMed]

15. B. J. Shen, H. X. Kang, D. L. Sun, Q. L. Zhang, S. T. Yin, P. Chen, and J. Liang, “Investigation of laser diode end pumped Er:YSGG/YSGG composite crystal lasers at 2.79 µm,” Laser Phys. Lett. 11(1), 015002 (2014). [CrossRef]

16. E. A. Arbabzadah, C. C. Phillips, and M. J. Damzen, “Free-running and Q-switched operation of a diode pumped Er:YSGG laser at the 3 μm transition,” Appl. Phys. B 111(2), 333–339 (2013). [CrossRef]

17. E. Arbabzadah, S. Chard, H. Amrania, C. Phillips, and M. Damzen, “Comparison of a diode pumped Er:YSGG and Er:YAG laser in the bounce geometry at the 3 μm transition,” Opt. Express 19(27), 25860–25865 (2011). [CrossRef] [PubMed]

18. B. J. Dinerman and P. F. Moulton, “3-μm cw laser operations in erbium-doped YSGG, GGG, and YAG,” Opt. Lett. 19(15), 1143–1145 (1994). [CrossRef] [PubMed]

19. B. J. Dinerman, “Spectroscopic characterization and 3-μm CW laser operation of Er³⁺:Gd₃Ga₅O₁₂ and Er³⁺:Y₃Sc₂Ga₃O₁₂,” Ph.D. dissertation, Boston College Graduate School of Arts and Sciences, Boston, 1994.

20. R. C. Stoneman and L. Esterowitz, “Efficient resonantly pumped 2.8-microm Er³⁺:GSGG laser,” Opt. Lett. 17(11), 816–818 (1992). [CrossRef] [PubMed]

21. J. Su, Q. Zhang, and S. Yin, “Research progress in crystals and lasers of YSGG series,” J. Synthetic Crystals 34(4), 709–713 (2005).

22. Z. Jia, X. Tao, C. Dong, M. Jiang, A. Arcangeli, S. Bigotta, and M. Tonelli, “Spectroscopic analysis of Nd³⁺ doped (Lu_x+ Gd_1−x)₃Ga₅O₁₂ crystal,” Appl. Phys. B 100(3), 485–491 (2010). [CrossRef]

23. J. C. Bourcett and F. K. Fong, “Quantum efficiency of diffusion limited energy transfer in La_1-x-yCe_xTbyPO₄,” J. Chem. Phys. 60(1), 34–39 (1974). [CrossRef]

24. J. K. Chen, D. Sun, J. Luo, J. Xiao, R. Dou, and Q. Zhang, “Er³⁺ doped GYSGG crystal as a new laser material resistant to ionizing radiation,” Opt. Commun. 301–302, 84–87 (2013). [CrossRef]

Crystals	Absorption cross-section (cm²)	Er³⁺:⁴I_11/2 lifetime (ms)	Er³⁺:⁴I_13/2 lifetime (ms)	Emission cross-section (cm²)	Ref.
50at%Er:YAG	–	0.12	7.25	3 × 10⁻²⁰ @2.936μm	[17]
10at%Er:GGG	1.03 × 10⁻²⁰ @965 nm	1.06	8.77	7.24 × 10⁻¹⁹ @2.7μm	[3]
35at%Er:GSGG	–	1.3	7.6	8.6 × 10⁻²⁰ @2.64 μm 10.3 × 10⁻²⁰ @2.79 μm	[13]
35at%Er:GYSGG	–	1.2	3.9	–	[24]
20at%Er,0.3at%Pr:GYSGG	1.6 × 10⁻²¹ @968 nm	0.52	0.60	4.7 × 10⁻¹⁹ @2.79 μm	[14]
1at%Yb,10at%Er,0.1at%Ho:GYSGG	1.47 × 10⁻²¹ @ 967 nm	1.23	4.92	1.4 × 10⁻¹⁹ @2.794 μm	[10]
20at%Er:YSGG	1.56 × 10⁻²¹ @ 790 nm	0.57	2.06	1.02 × 10⁻¹⁹ @2.64 μm	This work
5at%Nd,20at%Er:LuYSGG	5.25 × 10⁻²⁰ @ 808 nm	0.38	Quenched	1.84 × 10⁻¹⁹ @2.64 μm	This work

Dual function of Nd³⁺ in Nd,Er:LuYSGG crystal for LD pumped ~3.0 μm mid-infrared laser

Abstract

1. Introduction

2. Experimental details

3. Results and discussion

4. Conclusions

Acknowledgments

References and links

Cited By

Figures (6)

Tables (1)

Equations (4)

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