Abstract

We report an efficient room-temperature operation of a resonantly pumped Er3+:GdVO4 laser at 1598.5nm. The maximum continuous wave (CW) output power of 3.5W with slope efficiency of 56% was achieved with resonant pumping by an Er-fiber laser at 1538.6nm. With pumping by a commercial laser diode bar stack, a quasi-CW (QCW) output of 7.7W and maximum slope efficiency of 53% versus absorbed pump power were obtained. This is believed to be the first resonantly (in-band) pumped, room-temperature Er3+:GdVO4 laser.

©2012 Optical Society of America

Due to its good mechanical, thermo-optical, and spectroscopic properties, Er3+ doped GdVO4 is considered to be a promising laser material for efficient operation in the 1.6μm eye-safe wavelength domain [1,2]. Recently, a 0.42W CW output from a room-temperature (RT) Er3+:GdVO4 laser was demonstrated by Sulc et al [3]. This laser, pumped into the I11/24 manifold of the Er3+ ion at 977nm and emitting from the I13/24 manifold at 1598nm, has demonstrated a slope efficiency of 14% versus the absorbed pump. It has been shown that much higher efficiency can be demonstrated via resonant pumping directly into the I13/24 manifold. Such pumping allows for a low quantum defect (QD<3%) operation [4] and offers much better power scaling potential. This pump-lase scheme based on I15/24I13/24 transitions operates particularly well at cryogenic temperatures, and lately we reported 84% slope efficiency for a cryo-cooled resonantly (in-band) pumped Er3+:GdVO4 laser [5]. Also, the resonantly pumped RT Er3+:YVO4 laser (which is a very close analog of an Er3+:GdVO4 one) demonstrated slope efficiency of 57.9% [6]. Similar high efficiency can be expected for an RT Er:GdVO4 laser as well, but, to the best of our knowledge, laser efficiency of resonantly pumped Er3+:GdVO4 at RT has not been explored so far.

This paper presents the RT spectroscopic characterization of Er3+:GdVO4 in the 1450 to 1700nm range (I13/24I15/24 transitions) and reports the performance of what is believed to be the first RT in-band pumped Er3+:GdVO4 laser.

For spectroscopic characterization, we used the 0.5%-doped Er3+:GdVO4 crystal grown by the Czochralski technique. Absorption spectra between the I15/24 and the I13/24 multiplets were taken using a Cary 6000i spectrophotometer operating in the fixed-slit-width mode with 0.1nm resolution. Figure 1 shows polarization-resolved ground-state absorption spectra of Er3+:GdVO4. There are two strong π-polarized absorption lines: at 1502nm and around 1529nm. For σ polarization, there are three distinctive transitions with approximately equal strengths, spread between 1519 and 1539nm.

 figure: Fig. 1.

Fig. 1. Absorption cross sections of the I15/24I13/24 transitions of Er3+:GdVO4 for π and σ polarizations.

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Emission spectra of Er3+:GdVO4 were obtained by illuminating the 0.5%-doped sample with a 970nm diode laser. Luminescence was collected with the Optical Spectrum Analyzer (Yokogawa, model AQ6370C). A polarization beam splitter was inserted into collecting optics to separate σ- and π-polarized signals. The emission cross sections of the I13/24I15/24 transitions, shown in Fig. 2, were calculated via the standard Fuchtbauer–Landenburg method [7], using the lifetime of the I13/24 manifold of 3.06ms [5].

 figure: Fig. 2.

Fig. 2. Emission cross sections of the I13/24I15/24 transitions of Er3+:GdVO4 for π and σ polarizations.

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It can be seen that in the π-polarized emission spectrum of Er3+:GdVO4 there are three emission maxima where lasing can be expected: at 1598nm (cross section σem0.5×1020cm2), at 1590nm (σem0.25×1020cm2), and at 1576nm (σem0.5×1020cm2). The relevant energy level scheme of the I13/24 and the I15/24 manifolds can be found in [1] and in [5]. In the σ-polarized spectrum, there is one transition at 1587nm suitable for laser operation with the peak cross section of σemi0.4×1020cm2.

Laser experiments were carried out with the antireflection-coated, 10mm long, 3mm thick 0.7% Er3+:GdVO4 sample. The crystallographic c axis of the crystal was normal to the axis of the laser cavity, thus enabling longitudinal pumping in any chosen polarization. The crystal was bonded between copper plates water-cooled to +18°C. A simplified experimental laser setup is shown in Fig. 3.

 figure: Fig. 3.

Fig. 3. Simplified optical layout of the laser setup.

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Two different sources were used for pumping into major absorption lines of Er3+:GdVO4: a CW Er-fiber laser with narrowband output (0.3nm FWHM) and a commercial, spectrally narrowed (2nm FWHM), fast- and slow-axis collimated laser diode bar stack (QPC Lasers). The Er-fiber laser output wavelength was tuned to the 1538.6nm absorption band with large σ cross section and relatively small π cross section.

The unpolarized pump beam was focused into the crystal by the f=100mm spherical lens.

The diameter of the almost cylindrical pumped region inside the crystal was approximately 330μm (1/e2 level). The short laser cavity (Lcav40mm) consisting of a concave output coupler (RCC=100mm) and a flat dichroic mirror (T>95% at 15201540nm, R>99.5% at 15801650nm) resulted in the TEM00 mode diameter of 330μm for a good mode matching.

Figure 4 shows the CW output power of the Er3+:GdVO4 laser pumped by a 1538.6nm Er-fiber laser. The best efficiency was achieved with the 5% outcoupling. The maximum obtained output power was 3.5W, and the maximum slope efficiency 56%. The fraction of the absorbed pump, carefully derived from the measurements of the transmitted pump while the laser was operational, was calculated at 41% to 44%. This relatively low value is due to the weak absorption of the π-polarized component of the unpolarized pump. No noticeable heating of the crystal was observed. The output of the Er3+:GdVO4 laser was π-polarized and centered at 1598.2nm with the bandwidth varying from 1.5 to 2.5nm with the absorbed pump.

 figure: Fig. 4.

Fig. 4. Output power versus absorbed pump power for the CW Er3+:GdVO4 laser pumped by a narrow-linewidth Er-fiber laser at 1538.6nm. Red straight line represents the linear regression of the experimental data.

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The second pump source, the InGaAsP/InP laser diode bar stack, was operated in a QCW regime with a 5% duty cycle and tpulse=10ms. The incident pump beam was π polarized, and its wavelength was tuned to the 1529nm absorption band (cross section σabs2.6×1020cm2) by varying the coolant temperature of the stack. A 4× cylindrical telescope was used to provide a nearly equal divergence of the pump beam in the vertical and horizontal directions (see Fig. 3). A polarizing cube and a half-wave plate placed in front of the diode stack served as a variable pump attenuator. The collimated pump was focused into the crystal by a spherical lens (f=75mm). The diameter of the pump spot was 960μm in the center of the crystal and 1200μm at the crystal ends. We used a 55mm long laser cavity and concave output couplers with a curvature of 250mm. Their reflections varied from 80% to 95%. This cavity configuration provided a fairly good pump-cavity mode spatial overlap inside the crystal.

Figure 5 shows the QCW output power of the Er3+:GdVO4 laser versus the absorbed pump for 10% outcoupling. The maximum QCW output power of 7.7W and the maximum slope efficiency of 53% were obtained. The observed nonlinearity of the input-output plot is caused by a stronger radial variation of the excitation relative to the case of Er-fiber pumping. Thus, at low pump levels, only low-order modes are involved in lasing. With the gradual increase of pump power, the number of involved modes going into lasing increases, which improves overall efficiency of the laser.

 figure: Fig. 5.

Fig. 5. Output power versus absorbed pump power for the QCW Er3+:GdVO4 laser pumped by a spectrally narrowed laser diode bar stack at 1529nm. Red straight line represents the linear regression of the experimental data.

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The fraction of the absorbed pump power in this case was calculated as 0.5 when the laser operated just above the threshold. The fraction reduced to approximately 0.4 at the maximum of the absorbed pump (36W). This relatively low utilization of the incident pump power is due to a small cross section of the 1529nm absorption transition. As in the previous case, the π-polarized output spectrum was centered at 1598.2nm. Its full bandwidth reached 4nm at the maximum absorbed pump power.

We presented the results of a RT spectroscopic characterization of Er3+:GdVO4 single crystal in the spectral range pertinent to the resonantly (in-band) pumped I13/24I15/24 laser operation. We reported for the first time, to the best of our knowledge, the RT performance of the resonantly pumped Er3+:GdVO4 laser. The maximum CW output power of 3.5W at 1598.5nm with slope efficiency of 56% was achieved with Er-fiber laser pumping at 1538.6nm. With QCW pumping by a commercial laser diode bar stack at 1529nm, a QCW output power of 7.7W at 1598.5nm and maximum slope efficiency of 53% versus the absorbed pump power were demonstrated.

References

1. C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004). [CrossRef]  

2. R. Lisiecki, P. Solarz, G. Dominiak-Dzik, W. Ryba-Romanowski, and T. Lukasiewicz, Opt. Lett. 34, 3271 (2009). [CrossRef]  

3. J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September 2010, paper ThP7.

4. N. Ter-Gabrielyan, V. Fromzel, L. Merkle, and M. Dubinskii, Opt. Mater. Express 1, 223 (2011).

5. N. Ter-Gabrielyan, V. Fromzel, T. Lukasiewicz, W. Ryba-Romanowski, and M. Dubinskii, Opt. Express 20, 6080 (2012). [CrossRef]  

6. C. Brandt, V. Matrosov, K. Petermann, and G. Huber, Opt. Lett. 36, 1188 (2011). [CrossRef]  

7. W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962). [CrossRef]  

References

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  1. C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
    [Crossref]
  2. R. Lisiecki, P. Solarz, G. Dominiak-Dzik, W. Ryba-Romanowski, and T. Lukasiewicz, Opt. Lett. 34, 3271 (2009).
    [Crossref]
  3. J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.
  4. N. Ter-Gabrielyan, V. Fromzel, L. Merkle, and M. Dubinskii, Opt. Mater. Express 1, 223 (2011).
  5. N. Ter-Gabrielyan, V. Fromzel, T. Lukasiewicz, W. Ryba-Romanowski, and M. Dubinskii, Opt. Express 20, 6080 (2012).
    [Crossref]
  6. C. Brandt, V. Matrosov, K. Petermann, and G. Huber, Opt. Lett. 36, 1188 (2011).
    [Crossref]
  7. W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962).
    [Crossref]

2012 (1)

2011 (2)

2009 (1)

2004 (1)

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

1962 (1)

W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962).
[Crossref]

Bertini, C.

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

Brandt, C.

Cavalli, E.

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

Dexter, D. L.

W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962).
[Crossref]

Dominiak-Dzik, G.

Dubinskii, M.

Fowler, W. B.

W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962).
[Crossref]

Fromzel, V.

Huber, G.

Jelinkova, H.

J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.

Lisiecki, R.

Lukasiewicz, T.

N. Ter-Gabrielyan, V. Fromzel, T. Lukasiewicz, W. Ryba-Romanowski, and M. Dubinskii, Opt. Express 20, 6080 (2012).
[Crossref]

R. Lisiecki, P. Solarz, G. Dominiak-Dzik, W. Ryba-Romanowski, and T. Lukasiewicz, Opt. Lett. 34, 3271 (2009).
[Crossref]

J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.

Magnani, N.

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

Matrosov, V.

Merkle, L.

Petermann, K.

Ryba-Romanowski, W.

N. Ter-Gabrielyan, V. Fromzel, T. Lukasiewicz, W. Ryba-Romanowski, and M. Dubinskii, Opt. Express 20, 6080 (2012).
[Crossref]

R. Lisiecki, P. Solarz, G. Dominiak-Dzik, W. Ryba-Romanowski, and T. Lukasiewicz, Opt. Lett. 34, 3271 (2009).
[Crossref]

J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.

Solarz, P.

Sulc, J.

J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.

Ter-Gabrielyan, N.

Toncelli, A.

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

Tonelli, M.

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

J. Lumin. (1)

C. Bertini, A. Toncelli, M. Tonelli, E. Cavalli, and N. Magnani, J. Lumin. 106, 235 (2004).
[Crossref]

Opt. Express (1)

Opt. Lett. (2)

Opt. Mater. Express (1)

Phys. Rev. (1)

W. B. Fowler and D. L. Dexter, Phys. Rev. 128, 2154 (1962).
[Crossref]

Other (1)

J. Sulc, H. Jelinkova, W. Ryba-Romanowski, and T. Lukasiewicz, “Diode-pumped Er:GdVO4 eye-safe laser,” presented at 4th EPS-QEOD Europhoton Conference, Hamburg, Germany, September2010, paper ThP7.

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Figures (5)

Fig. 1.
Fig. 1. Absorption cross sections of the I15/24I13/24 transitions of Er3+:GdVO4 for π and σ polarizations.
Fig. 2.
Fig. 2. Emission cross sections of the I13/24I15/24 transitions of Er3+:GdVO4 for π and σ polarizations.
Fig. 3.
Fig. 3. Simplified optical layout of the laser setup.
Fig. 4.
Fig. 4. Output power versus absorbed pump power for the CW Er3+:GdVO4 laser pumped by a narrow-linewidth Er-fiber laser at 1538.6nm. Red straight line represents the linear regression of the experimental data.
Fig. 5.
Fig. 5. Output power versus absorbed pump power for the QCW Er3+:GdVO4 laser pumped by a spectrally narrowed laser diode bar stack at 1529nm. Red straight line represents the linear regression of the experimental data.

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