OSA's Digital Library

Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 10 — May. 20, 2013
  • pp: 12460–12468
« Show journal navigation

Laser operation of a Tm:Y2O3 planar waveguide

Jakub W. Szela, Katherine A. Sloyan, Tina L. Parsonage, Jacob I. Mackenzie, and Robert W. Eason  »View Author Affiliations


Optics Express, Vol. 21, Issue 10, pp. 12460-12468 (2013)
http://dx.doi.org/10.1364/OE.21.012460


View Full Text Article

Acrobat PDF (1012 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We demonstrate the first Tm-doped yttria planar waveguide laser to our knowledge, grown by pulsed laser deposition. A maximum output power of 35 mW at 1.95 μm with 9% slope efficiency was achieved from a 12 μm-thick film grown on a Y3Al5O12 substrate.

© 2013 OSA

1. Introduction

Lasers operating in the 2 micron wavelength region have a number of applications, including remote sensing/LIDAR, materials processing and medical therapy. Thulium-doped media have several attractive features for generating light in this wavelength band, including a broad emission bandwidth, long-lived metastable states, absorption bands matched to high-power 0.8 μm diode-pump sources, and the potential for high quantum efficiency due to a 2-for-1 cross-relaxation process [1

1. J. I. Mackenzie, C. Li, D. P. Shepherd, R. J. Beach, and S. C. Mitchell, “Modeling of high-power continuous-wave Tm:YAG side-pumped double-clad waveguide lasers,” IEEE J. Quantum Electron. 38, 222–230 (2002) [CrossRef] .

, 2

2. L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.

]. Waveguide lasers are compact, can be easily integrated with diode pump lasers without additional beam shaping, can have lower thresholds than bulk geometries and have excellent thermal management properties. These are all features that are highly desirable in many 2 micron applications, particularly where high pump and output powers are desired.

Rare earth (RE) sesquioxides, including doped Sc2O3 (scandia), Y2O3 (yttria) and Lu2O3 (lutetia) are of great interest as potential waveguide laser hosts. These cubic materials have excellent thermo-optic properties and can easily be doped with various RE ions (including thulium) and are optically isotropic. Sesquioxides can, however, be challenging to grow from the melt due to their relatively high melting points (generally in excess of 2400 °C) [3

3. V. Peters, A. Bolz, K. Petermann, and G. Huber, “Growth of high-melting sesquioxides by the heat exchanger method,” J. Cryst. Growth 237–239879–883 (2002) [CrossRef] .

].

Pulsed laser deposition (PLD) is a simple but versatile thin film deposition technique that has proven suitable for growth of low-loss lasing waveguides [4

4. C. Grivas, D. P. Shepherd, T. C. May-Smith, R. W. Eason, and M. Pollnau, “Single-transverse-mode Ti:sapphire rib waveguide laser,” Opt. Express 13, 210–215 (2005) [CrossRef] [PubMed] .

, 5

5. C. Grivas, T. C. May-Smith, D. P. Shepherd, and R. W. Eason, “Laser operation of a low loss (0.1 dBcm−1) Nd:Gd3Ga5O12thick (40 μm) planar waveguide grown by pulsed laser deposition,” Opt. Commun. 229, 355–361 (2004) [CrossRef] .

]. Despite the high growth temperatures required for deposition (∼700 °C or above), growth of various sesquioxide films has been achieved via PLD [6

6. T. Gun, A. Kahn, B. Ileri, K. Petermann, and G. Huber, “Two-dimensional growth of lattice matched Nd-doped (Gd,Lu)2O3films on Y2O3by pulsed laser deposition,” Appl. Phys. Lett. 93, 053108 (2008) [CrossRef] .

, 7

7. E. R. Smith, J. B. Gruber, P. Wellenius, J. F. Muth, and H. O. Everitt, “Spectra and energy levels of Eu3+in cubic phase Gd2O3,” Phys. Status Solidi B , 247, 1807–1813 (2010) [CrossRef] .

], including doped and undoped Y2O3[8

8. P. B. W. Burmester, G. Huber, M. Kurfiss, and M. Schilling, “Crystalline growth of cubic (Eu, Nd):Y2O3thin films on α-Al2O3,” Appl. Phys. A. 80, 627–360 (2005) [CrossRef] .

11

11. A. K. Singh, T. R. G. Kutty, and S. Sinha, “Pulsed laser deposition of corrosion protective Yttrium Oxide (Y2O3) coating,” J. Nucl. Mater. 420, 374–381 (2012) [CrossRef] .

]. Lasing has been observed in Nd:(Gd,Lu)2O3[12

12. A. Kahn, S. Heinrich, H. Kühn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Low threshold monocrystalline Nd:(Gd, Lu)2O3channel waveguide laser,” Opt. Express 17,(6) 4112–4118 (2009) [CrossRef] .

] and Yb:(Gd,Lu)2O3[13

13. H. Kühn, S. Heinrich, A. Kahn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Monocrystalline Yb3+:(Gd,Lu)2O3channel waveguide laser at 976.8 nm,” Opt. Lett. 34, 2718–2720 (2009) [CrossRef] .

] channel waveguides formed by post-processing of PLD-grown films. Estimated optical losses (propagation + unquantified coupling losses) in these latter cases have, however, been high (>4 dBcm−1), and thicknesses limited to ∼2 μm.

In this paper we present the growth and laser operation of a 12 μm-thick Tm3+:Y2O3 planar waveguide grown on a Y3Al5O12 (YAG) substrate by PLD, representing the first example to our knowledge of a Tm:Y2O3 waveguide laser. Threshold pump power and slope efficiency were determined to be 135 mW and 9% respectively, leading to a maximum output power of 35 mW measured for a maximum pump power of 600 mW; this is, to our knowledge, the highest output power recorded for a sesquioxide laser grown by PLD by more than a factor of two.

2. Film fabrication and characterization

2.1. Fabrication

The ∼12 μm-thick film was deposited onto a (100)-oriented YAG substrate of size 10×10×1 mm3 via the experimental setup displayed in Fig. 1. KrF excimer laser pulses of wavelength 248 nm, duration 20 ns and fluence 1.7 Jcm−2 were incident upon a Tm:doped ceramic yttria target. The substrate was heated to ∼1000 °C via a CO2 laser of wavelength 10.6 μm, incident upon a ZnSe tetraprism to obtain a square beam profile [14

14. T. C. May-Smith, A. C. Muir, M. S. B. Darby, and R. W. Eason, “Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2laser for pulsed laser deposition experiments,” Appl. Optics 47, 1767–1780 (2008) [CrossRef] .

]. The target was rotated, driven by an offset cam assembly, providing an epitrochoidal ablation path and hence efficient use of the target surface. Deposition took place in a background oxygen gas pressure of 4×10−2 mbar. Following material charaterization, two opposing facets were polished plane and parallel for lasing experiments, resulting in a final waveguide length of ∼8 mm.

Fig. 1 Diagram of experimental setup, including UV ablating and IR heating laser beams.

2.2. Material characterization

X-ray diffraction (XRD) was carried out using a Bruker D2 Phaser powder diffractometer. XRD data was obtained for films on substrates and the bare substrates to allow peaks resulting from diffraction from the substrate to be identified. A KLA Tencor P16 stylus profiler was used to measure film thickness and a Zemetrics Zescope optical profiler was used to obtain 3D surface profile maps, allowing automatic particulate counting with the Image Metrology Scanning Probe Image Processor (SPIP) software package.

The film was crystalline, as was demonstrated by the XRD spectrum shown in Fig. 2(a). The largest peaks correspond to (222) and (444) orientations of the film, as well as the (400) and (800) orientations of the underlying YAG substrate, indicating that the film is highly textured in the (222) orientation. (222)-oriented growth has been observed previously in sesquioxide deposition, both where the film and substrate were lattice matched (for example in the case of growth of yttria on sapphire, where the lattice mismatch was ∼5% [8

8. P. B. W. Burmester, G. Huber, M. Kurfiss, and M. Schilling, “Crystalline growth of cubic (Eu, Nd):Y2O3thin films on α-Al2O3,” Appl. Phys. A. 80, 627–360 (2005) [CrossRef] .

]), and in the case of growth on amorphous substrates (where there is no lattice match, growth in the cubic phase and {111} orientation minimises the surface free energy [15

15. O. Pons-Y-Moll, J. Perrier, E. Millon, R. M. Defourneau, D. Defourneau, B. Vincent, A. Essahlaoui, A. Boudrioua, and W. Seiler, “Structural and optical properties of rare-earth-doped Y2O3waveguides grown by pulsed-laser deposition,” J. Appl. Phys. 92, 4885–4890 (2002) [CrossRef] .

]). A number of peaks at least two orders of magnitude smaller than the primary (222) orientation peak can also be observed. This indicates a small amount of growth in other orientations and possibly in a non-cubic phase (corresponding to the peak labelled A). This latter peak could not be assigned directly from database values, although a number of non-cubic orientations of Y2O3 exhibit peaks at a similar value of 2θ [16

16. “Inorganic Crystal Structure Database,” http://icsd.cds.rsc.org/

].

Fig. 2 XRD spectra of (a) the 12 μm-thick Tm3+:Y2O3 waveguide and (b) a 50 nm-thick Tm3+:Y2O3 film. Very small peaks corresponding to growth in orientations other than the primary (222) and (444) orientation can be observed, particularly in case (a). Unassigned film peaks are observed around 26.4° (A) and 17.6° (E). Peaks arising from substrate contributions may also be observed: peaks labelled B and C may correspond to orientations of cubic yttria, while peaks D, F and G likely correspond to orientations of YAlO3.

For comparison, a 50 nm Tm3+:Y2O3 film was grown under the same deposition conditions, the XRD spectrum of which is shown in Fig. 2(b). In this case, only peaks corresponding to the (222) and (444) planes of cubic yttria can be observed, as well as additional small peaks around 17.6° (E) and 26.4° (A). This suggests that the film grows primarily in the (222) orientation even during the first tens of nanometres of growth, while growth in other orientations becomes more prevalent as the film thickness increases. A very small peak likely corresponding to the non-cubic yttria phase is also observed around 26.4°, indicating some growth in this phase even at these small thickness values.

The growth mechanisms that lead to the formation of cubic and non-cubic phases in different orientations, as well as their changing significance as film thickness increases, are currently under investigation. It should be noted that due to the small thickness of the film, the XRD spectrum is dominated by the substrate contribution, and peaks resulting from the film itself (i.e. small amounts of growth in other phases/orientations) may be lost in the noise. It should also be noted that the presence of peaks other than (400) and (800) orientations of YAG in the substrate spectra indicates that the substrates themselves are not perfect crystal, which may be influencing subsequent film growth. The peaks labelled B and C in Fig. 2(a) may correspond to the (211) and (440) orientations of cubic yttria, while peaks labelled D, F and G in Figs. 2(a) and 2(b) likely correspond to the (222), (111) and (221) orientations of YAlO3 (YAP) respectively.

2.3. Waveguide characterization

Considering the refractive index of the YAG [17

17. D. E. Zelmon, D. L. Small, and R. Page, “Refractive-index measurements of undoped yttrium aluminum garnet from 0.4 to 5.0 μm,” Appl. Opt. 37(21), 4933–4935 (1998) [CrossRef] .

] substrate and undoped Y2O3[18

18. W. J. Tropf, M. E. Thomas, and E. W. Rogala, “Properties of crystals and glasses,” in Handbook of Optics, 3rd editionM. Bass, ed. (McGraw Hill Professional, 2010).

] (1.82 and 1.91 respectively at 800 nm), and noting that this Tm dopant concentration likely results in a negligible index increase, the numerical aperture (NA) of the waveguide at the pump and lasing wavelengths was calculated to be 0.58 and 0.57 respectively. The 12 μm-thick film should hence support up to 50 and 20 modes at the pump and laser wavelengths respectively, and is therefore a highly multi-mode structure.

Propagation losses were estimated through transmission measurements at wavelengths outside of the Tm3+ 3H4 manifold absorption band using a tunable Ti:sapphire laser, specifically 730 nm and 850 nm. Assuming a 100% launch efficiency, the loss coefficient γ can be calculated using Eq. (1):
γ=ln(PoutPin(1R)2)/lw
(1)
where lw is the waveguide length, R is the Fresnel reflectance at each waveguide facet and Pin/out are the respective incident and out-coupled powers of the probe beam. For our 8 mm-long waveguide, assuming the Fresnel reflectance of pure yttria R = 9.9%, losses are estimated to be ∼2 dBcm−1 at the probe wavelengths (losses at longer wavelengths are expected to be lower due to a smaller Rayleigh scattering coefficient).

The average density of particulates of height >100 nm and >50 nm on the film surface was measured as (9.8± 1.3)×103 cm−2 and (15 ± 2.4)×104 cm−2 respectively. Barrington et al [19

19. S. J. Barrington, T. Bhutta, D. P. Shepherd, and R. W. Eason, “The effect of particulate density on performance of Nd:Gd3Ga5O12 waveguide lasers grown by pulsed laser deposition,” Opt. Commun. 185, 145–152 (2000) [CrossRef] .

] analysed the effect of particulates on propagation loss in PLD-grown laser waveguides based on films of G3Ga5O12 (GGG), a cubic crystal with a similar refractive index to yttria (∼1.96), grown on YAG substrates. While a direct comparison of loss values may not be valid due to the difference in material properties and growth conditions, it can still be helpful as a guide. In the GGG case, the particulate densities we have measured would be expected to result in losses of much lower than 1 dBcm−1. Our estimated losses of ∼2 dBcm−1 hence suggest that particulates may not be the only source of loss in our waveguide. Other factors potentially resulting in additional scattering and subsequent loss (not quantified) include local areas of poor-quality facet polishing and strain-induced birefringence, as well as scattering at grain boundaries and/or areas of non-cubic growth. It is expected that further study of film growth mechanisms may help to explain these additional sources of loss.

To determine the optimum pump wavelength, the relative absorption spectrum of the waveguide was measured by tuning the Ti:sapphire pump laser in 0.1 nm steps across a range of 790–810 nm (see Fig. 3). The maximum absorption coefficient α was determined to be 1.45 cm−1 at a pump wavelength λp = 796.5 nm, corrected for the propagation losses determined at the out-of-band (i.e. non-absorbing) probe wavelengths, consistent with that observed in bulk crystal [2

2. L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.

, 22

22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

]. Previously reported absorption cross section data is shown in Fig. 3 for comparison.

Fig. 3 Measured variation in absorption coefficient of the Tm:Y2O3 film with wavelength (black), with previously reported absorption cross section data for bulk crystal [22] shown for comparison (red).

2.4. Spectroscopic characterization

Lifetime and emission measurements were performed at room temperature. The Tm3+ ions were excited to their 3H4 level using the output of a fibre-coupled laser diode operating at 793 nm. The pump beam was focussed onto the face of the waveguide, perpendicular to the plane of the film and close to one edge; while the 2 μm fluorescence from the 3F4 energy level, was captured as it exited the waveguide facet. At 3 W peak power and with a pump beam size at the film of 600 μm diameter, the incident irradiance was Ip = 1 kWcm−2. The waveguide facet and 2 μm emission were reimaged onto a Thorlabs DET10D InGaAs detector with a germanium filter covering the active area, passing only the longer wavelength of interest. To determine the lifetime of the upper laser level the pump was modulated with 5 ms pulses at a 10% duty cycle (i.e. 5 ms pulse at a period of 50 ms), enough time for the system to reach steady-state conditions.

A fluorescence lifetime of τ = 3.44 ± 0.01 ms was determined from the exponential decaying signal recorded using an Agilent MSO6104A digital oscilloscope. This is in good agreement with values reported for bulk Tm3+:Y2O3 with lifetimes of 4.15 ms (1 at.% Tm3+[2

2. L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.

]) and 3.2 ms (2 at.% Tm3+[20

20. Y. Guyot, R. Moncorgé, L. D. Merkle, A. Pinto, B. McIntosh, and H. Verdun, “Luminescence properties of Y2O3single crystals doped with Pr3+or Tm3+and codoped with Yb3+, Tb3+or Ho3+ions,” Opt. Mater. 5, 127–136 (1996) [CrossRef] .

]). Figure 4 shows the emission spectrum measured with an ANDO AQ6375 optical spectrum analyser using a spectral bandwidth of 2 nm, along with data observed for bulk crystal [20

20. Y. Guyot, R. Moncorgé, L. D. Merkle, A. Pinto, B. McIntosh, and H. Verdun, “Luminescence properties of Y2O3single crystals doped with Pr3+or Tm3+and codoped with Yb3+, Tb3+or Ho3+ions,” Opt. Mater. 5, 127–136 (1996) [CrossRef] .

] for comparison. The spectral profiles of waveguide and bulk are almost identical. This agreement indicates correct substitutional occupation for the thulium ions, which is not always the case for PLD grown thin films; in the case of GGG growth on YAG, for example, the spectral match between bulk and film crystal is poor due to non-stoichiometric growth and incorporation of RE ions in non-radiative sites [21

21. A. A. Anderson, C. L. Bonner, D. P. Shepherd, R. W. Eason, C. Grivas, D. S. Gill, and N. Vainos, “Low loss (0.5 dB/cm) Nd:Gd3Ga5O12 waveguide layers grown by pulsed laser deposition,” Opt. Commun. 183–186 (1997).

].

Fig. 4 Measured fluorescence emission spectrum of the Tm3+:Y2O3 waveguide (black), with data previously observed for bulk crystal [20] shown for comparison (red).

3. Laser experiments

2 μm laser emission from the 3F43H6 transition of Tm3+ starts with excitation into the 3H4 manifold and subsequent population redistribution either by cross-relaxation or energy migration into the 3F4 metastable level. The former process can provide an efficient pumping mechanism with up to two excited ions created for one pump photon, as has been exploited previously in a high-power Tm3+:YAG planar waveguide laser [1

1. J. I. Mackenzie, C. Li, D. P. Shepherd, R. J. Beach, and S. C. Mitchell, “Modeling of high-power continuous-wave Tm:YAG side-pumped double-clad waveguide lasers,” IEEE J. Quantum Electron. 38, 222–230 (2002) [CrossRef] .

]. This effect is dependent upon the proximity of the Tm3+ to neighbouring dopant ions, hence the higher RE ion concentration for yttria per atomic substitution (compared to YAG) should enable sufficient cross-relaxation rates at lower doping levels as reportedly used in early bulk crystal experiments [22

22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

].

The experimental setup of the end-pumped laser is depicted in Fig. 5. It consists of a tunable Ti:sapphire pump laser, a 100 mm focal length cylindrical lens, an 11 mm focal length aspheric lens, a thin pump input coupling mirror (IC), the waveguide, and various interchangeable bulk output coupling mirrors (OC). A collection lens (NA = 0.16) was used after the output coupling mirror to transfer the 2 μm light to a thermal detector covered by a 3 mm-thick longpass filter to reject the transmitted pump light.

Fig. 5 Setup of the Tm3+:Y2O3 waveguide lasing experiments. Abbreviations are as follows: MM – metal mirror; L1 – in-plane collimating cylindrical lens; L2 – aspheric lens; IC – input coupling mirror; OC – interchangeable output coupling mirror; L3 – collection lens.

The near-diffraction-limited pump source was tuned to match the maximum absorption peak around 797 nm and its optical power set by a variable metallic neutral density filter, providing a maximum incident power of 600 mW after the variable filter. In the waveguide’s fast-axis (guiding direction), the incident pump light was focused down to a waist of 3.6 μm at the input facet, significantly smaller than half the thickness of the active layer. The NA of the input pump lens was 0.25, much less than the acceptance NA of the waveguide, hence our assumption for a 100% launch efficiency (neglecting interface reflections). In the other (unguided) direction the beam was either collimated, with a beam waist of 90 μm positioned approximately midway along the waveguide, or diverging from the pump focus at the input facet i.e. a beam waist of 3.6 μm. The former configuration, achieved by placing the cylindrical lens before the input coupling aspheric, provided a good overlap between the pump beam width and cavity mode in the unguided axis throughout the whole waveguide. The latter configuration, however, provided higher inversion density at the input facet, at the expense of the overlap efficiency: the pump beam radius spread to ∼350 μm at the exit facet of the waveguide (calculated assuming no lensing effects in the plane), and was hence significantly larger than the ∼75 μm-radius cavity mode.

A quasi-monolithic optical resonator was made by butt-coupling plane parallel mirrors to the uncoated waveguide facets with a Fluorinert FC-70 fluid interface for the thin mirrors, holding them in place and acting as an index matching fluid. Four different OCs were investigated in total, with reflectance values of ∼99.5%, 94%, 90% and 85% at the laser wavelength. The pump transmittance of the HR IC was 92% and each of the other mirrors also had high transmission at this wavelength, leading to a single pass of the pump light. The waveguide was fixed to an aluminium pedestal on a 3-axis translation stage and was not actively cooled.

Laser action was observed for both pump configurations, with the respective performance shown in Fig. 6. Despite an emission cross section that extends out to 2.1 μm [2

2. L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.

], in all cases a laser wavelength of ∼1950 nm was observed, consistent with that reported for bulk crystal experiments [22

22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

]. This is due to the fact that the terminating laser level is in the ground-state, and the effective gain is dependent upon the difference between the emission and absorption cross sections at the lasing wavelength. Due to the relatively high gains required to overcome the losses in our system, and given that an effective inversion between the ground and upper laser level, β, of greater than 12% favours the shorter wavelengths [22

22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

], it is clear why this wavelength is observed for this system; it should be noted that for β >20% the emission wavelength would most likely switch to ∼1933 nm, where the strongest emission cross section occurs [22

22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

].

Fig. 6 Laser output power versus incident pump power for configuration (a) collimated in-plane pump (aspheric and cylindrical coupling lenses), and (b) diverging in-plane pump (single aspheric coupling lens).

With a HR+HR cavity the lowest observed laser threshold in the first configuration was 50 mW. Higher output power was achieved in the second configuration with only the aspheric input coupling lens, as can be seen in Fig. 6(b). A maximum output power was obtained with the 85% reflective OC, with 35 mW measured for 600 mW of incident pump power with a slope efficiency of ∼9%. The same slope efficiency was observed for the lowest reflectance OC in both configurations. A scanning slit beam profiler (Datarays Beam Scope P8, InAs detector with a single 5 μm slit width), horizontally and vertically matched to the generated laser beam, was used to estimate the beam quality parameter (M2) in the guided direction. A value of 5 ± 2.9 was obtained at full laser power.

Optical round trip losses were estimated by measuring the relaxation oscillation (RO) frequency as a function of the pump power with respect to the threshold power, including reabsorption at the laser wavelength [23

23. J. R. Salcedo, J. M. Sousa, and V. V. Kuzmin, “Theoretical treatment of relaxation oscillations in quasi-three-level systems,” Appl. Phys. B 62, 83–85 (1996) [CrossRef] .

]. The experimental setup was similar to Fig. 5, but with the addition of a mechanical chopper placed before the input coupling lenses. The thermal detector was replaced by a biased InGaAs detector connected to a digital oscilloscope.

For a system with reabsorption losses, the RO angular frequency ωRO is given by Eq. (2) [23

23. J. R. Salcedo, J. M. Sousa, and V. V. Kuzmin, “Theoretical treatment of relaxation oscillations in quasi-three-level systems,” Appl. Phys. B 62, 83–85 (1996) [CrossRef] .

]:
ωRO2=γcγτ(1+Nσalcnγc)(PpPpth1)
(2)
where γc is the cavity decay rate, γτ is the fluorescence decay rate, Pp is the pump power, Pth is the threshold pump power, N is thulium concentration, σal is the absorption cross section at the laser wavelength, c is the speed of light in vacuum, and n is the refractive index of the active medium at the laser wavelength. The loss L is obtained from the gradient of the linear fit to the RO angular frequencies, as per Eq. (2) and shown in Fig. 7, through the cavity decay rate γc, and other physical parameters via Eq. (3):
L=11RinRoutexp(2γcloptc)
(3)
where Rin and Rout are reflectance values for the IC and OC mirrors and lopt is the optical path length of the cavity. A round trip loss value of L = 5.8 ± 0.7 dB was obtained for the HR+HR cavity, highlighting that additional losses were incurred at the mirror/facet interfaces in comparison to the simple propagation losses measurement in section 2.3. Even higher round trip losses were obtained for the bulk OCs, a consequence of the small gap between the waveguide facet and mirror.

Fig. 7 Round trip cavity losses as determined via the measured relaxation oscillations

4. Conclusion

In summary, we have demonstrated the first Tm-doped yttria planar waveguide laser to our knowledge, grown by PLD. A maximum output power of 35 mW at 1.95 μm was achieved with a 9% slope efficiency. The 12 μm-thick film was highly textured in the {111} orientation with an average particulate density of (9.8 ± 1.3)×103 cm−2 (particulates of height >100 nm). Moderate propagation and mirror coupling losses currently limit the performance, as there was no sign of roll-over in the power curve even at the relatively high pump power densities investigated without any active cooling. Further improvement in performance is expected with improved film quality and direct coating of the waveguide end-facets, opening up a range of potential 2 μm high power applications from these compact gain modules.

Acknowledgments

This work has been funded under EPSRC grants EP/J008052/1 and EP/H005412/1. K.A. Sloyan acknowledges the support of an EPSRC Doctoral Prize, while T.L. Parsonage and J.W. Szela acknowledge the support of EPSRC studentships. J.W. Szela also acknowledges the support of Laser Quantum Ltd.

References and links

1.

J. I. Mackenzie, C. Li, D. P. Shepherd, R. J. Beach, and S. C. Mitchell, “Modeling of high-power continuous-wave Tm:YAG side-pumped double-clad waveguide lasers,” IEEE J. Quantum Electron. 38, 222–230 (2002) [CrossRef] .

2.

L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.

3.

V. Peters, A. Bolz, K. Petermann, and G. Huber, “Growth of high-melting sesquioxides by the heat exchanger method,” J. Cryst. Growth 237–239879–883 (2002) [CrossRef] .

4.

C. Grivas, D. P. Shepherd, T. C. May-Smith, R. W. Eason, and M. Pollnau, “Single-transverse-mode Ti:sapphire rib waveguide laser,” Opt. Express 13, 210–215 (2005) [CrossRef] [PubMed] .

5.

C. Grivas, T. C. May-Smith, D. P. Shepherd, and R. W. Eason, “Laser operation of a low loss (0.1 dBcm−1) Nd:Gd3Ga5O12thick (40 μm) planar waveguide grown by pulsed laser deposition,” Opt. Commun. 229, 355–361 (2004) [CrossRef] .

6.

T. Gun, A. Kahn, B. Ileri, K. Petermann, and G. Huber, “Two-dimensional growth of lattice matched Nd-doped (Gd,Lu)2O3films on Y2O3by pulsed laser deposition,” Appl. Phys. Lett. 93, 053108 (2008) [CrossRef] .

7.

E. R. Smith, J. B. Gruber, P. Wellenius, J. F. Muth, and H. O. Everitt, “Spectra and energy levels of Eu3+in cubic phase Gd2O3,” Phys. Status Solidi B , 247, 1807–1813 (2010) [CrossRef] .

8.

P. B. W. Burmester, G. Huber, M. Kurfiss, and M. Schilling, “Crystalline growth of cubic (Eu, Nd):Y2O3thin films on α-Al2O3,” Appl. Phys. A. 80, 627–360 (2005) [CrossRef] .

9.

A. Huignard, A. Aron, P. Aschehoug, B. Viana, J. Théry, A. Laurent, and J. Perrière, “Growth by laser ablation of Y2O3and Tm:Y2O3thin films for optical applications,” J. Mater. Chem. 10, 549–554 (2000) [CrossRef] .

10.

S. Zhang and R. Xiao, “Yttrium oxide films prepared by pulsed laser deposition,” J. Appl. Phys. 83, 3842–3848 (1998) [CrossRef] .

11.

A. K. Singh, T. R. G. Kutty, and S. Sinha, “Pulsed laser deposition of corrosion protective Yttrium Oxide (Y2O3) coating,” J. Nucl. Mater. 420, 374–381 (2012) [CrossRef] .

12.

A. Kahn, S. Heinrich, H. Kühn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Low threshold monocrystalline Nd:(Gd, Lu)2O3channel waveguide laser,” Opt. Express 17,(6) 4112–4118 (2009) [CrossRef] .

13.

H. Kühn, S. Heinrich, A. Kahn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Monocrystalline Yb3+:(Gd,Lu)2O3channel waveguide laser at 976.8 nm,” Opt. Lett. 34, 2718–2720 (2009) [CrossRef] .

14.

T. C. May-Smith, A. C. Muir, M. S. B. Darby, and R. W. Eason, “Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2laser for pulsed laser deposition experiments,” Appl. Optics 47, 1767–1780 (2008) [CrossRef] .

15.

O. Pons-Y-Moll, J. Perrier, E. Millon, R. M. Defourneau, D. Defourneau, B. Vincent, A. Essahlaoui, A. Boudrioua, and W. Seiler, “Structural and optical properties of rare-earth-doped Y2O3waveguides grown by pulsed-laser deposition,” J. Appl. Phys. 92, 4885–4890 (2002) [CrossRef] .

16.

“Inorganic Crystal Structure Database,” http://icsd.cds.rsc.org/

17.

D. E. Zelmon, D. L. Small, and R. Page, “Refractive-index measurements of undoped yttrium aluminum garnet from 0.4 to 5.0 μm,” Appl. Opt. 37(21), 4933–4935 (1998) [CrossRef] .

18.

W. J. Tropf, M. E. Thomas, and E. W. Rogala, “Properties of crystals and glasses,” in Handbook of Optics, 3rd editionM. Bass, ed. (McGraw Hill Professional, 2010).

19.

S. J. Barrington, T. Bhutta, D. P. Shepherd, and R. W. Eason, “The effect of particulate density on performance of Nd:Gd3Ga5O12 waveguide lasers grown by pulsed laser deposition,” Opt. Commun. 185, 145–152 (2000) [CrossRef] .

20.

Y. Guyot, R. Moncorgé, L. D. Merkle, A. Pinto, B. McIntosh, and H. Verdun, “Luminescence properties of Y2O3single crystals doped with Pr3+or Tm3+and codoped with Yb3+, Tb3+or Ho3+ions,” Opt. Mater. 5, 127–136 (1996) [CrossRef] .

21.

A. A. Anderson, C. L. Bonner, D. P. Shepherd, R. W. Eason, C. Grivas, D. S. Gill, and N. Vainos, “Low loss (0.5 dB/cm) Nd:Gd3Ga5O12 waveguide layers grown by pulsed laser deposition,” Opt. Commun. 183–186 (1997).

22.

F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.

23.

J. R. Salcedo, J. M. Sousa, and V. V. Kuzmin, “Theoretical treatment of relaxation oscillations in quasi-three-level systems,” Appl. Phys. B 62, 83–85 (1996) [CrossRef] .

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.5680) Lasers and laser optics : Rare earth and transition metal solid-state lasers
(220.4610) Optical design and fabrication : Optical fabrication
(230.7390) Optical devices : Waveguides, planar

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: March 13, 2013
Revised Manuscript: May 2, 2013
Manuscript Accepted: May 3, 2013
Published: May 14, 2013

Citation
Jakub W. Szela, Katherine A. Sloyan, Tina L. Parsonage, Jacob I. Mackenzie, and Robert W. Eason, "Laser operation of a Tm:Y2O3 planar waveguide," Opt. Express 21, 12460-12468 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-10-12460


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. J. I. Mackenzie, C. Li, D. P. Shepherd, R. J. Beach, and S. C. Mitchell, “Modeling of high-power continuous-wave Tm:YAG side-pumped double-clad waveguide lasers,” IEEE J. Quantum Electron.38, 222–230 (2002). [CrossRef]
  2. L. Fornasiero, N. Berner, B.-M. Dicks, E. Mix, V. Peters, K. Petermann, and G. Huber, “Broadly tunable laser emission from Tm:Y2O3and Tm:Sc2O3at 2 μm,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds. (Optical Society of America, 1999), paper WD5.
  3. V. Peters, A. Bolz, K. Petermann, and G. Huber, “Growth of high-melting sesquioxides by the heat exchanger method,” J. Cryst. Growth237–239879–883 (2002). [CrossRef]
  4. C. Grivas, D. P. Shepherd, T. C. May-Smith, R. W. Eason, and M. Pollnau, “Single-transverse-mode Ti:sapphire rib waveguide laser,” Opt. Express13, 210–215 (2005). [CrossRef] [PubMed]
  5. C. Grivas, T. C. May-Smith, D. P. Shepherd, and R. W. Eason, “Laser operation of a low loss (0.1 dBcm−1) Nd:Gd3Ga5O12thick (40 μm) planar waveguide grown by pulsed laser deposition,” Opt. Commun.229, 355–361 (2004). [CrossRef]
  6. T. Gun, A. Kahn, B. Ileri, K. Petermann, and G. Huber, “Two-dimensional growth of lattice matched Nd-doped (Gd,Lu)2O3films on Y2O3by pulsed laser deposition,” Appl. Phys. Lett.93, 053108 (2008). [CrossRef]
  7. E. R. Smith, J. B. Gruber, P. Wellenius, J. F. Muth, and H. O. Everitt, “Spectra and energy levels of Eu3+in cubic phase Gd2O3,” Phys. Status Solidi B, 247, 1807–1813 (2010). [CrossRef]
  8. P. B. W. Burmester, G. Huber, M. Kurfiss, and M. Schilling, “Crystalline growth of cubic (Eu, Nd):Y2O3thin films on α-Al2O3,” Appl. Phys. A.80, 627–360 (2005). [CrossRef]
  9. A. Huignard, A. Aron, P. Aschehoug, B. Viana, J. Théry, A. Laurent, and J. Perrière, “Growth by laser ablation of Y2O3and Tm:Y2O3thin films for optical applications,” J. Mater. Chem.10, 549–554 (2000). [CrossRef]
  10. S. Zhang and R. Xiao, “Yttrium oxide films prepared by pulsed laser deposition,” J. Appl. Phys.83, 3842–3848 (1998). [CrossRef]
  11. A. K. Singh, T. R. G. Kutty, and S. Sinha, “Pulsed laser deposition of corrosion protective Yttrium Oxide (Y2O3) coating,” J. Nucl. Mater.420, 374–381 (2012). [CrossRef]
  12. A. Kahn, S. Heinrich, H. Kühn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Low threshold monocrystalline Nd:(Gd, Lu)2O3channel waveguide laser,” Opt. Express17,(6) 4112–4118 (2009). [CrossRef]
  13. H. Kühn, S. Heinrich, A. Kahn, K. Petermann, J. D. B. Bradley, K. Wörhoff, M. Pollnau, and G. Huber, “Monocrystalline Yb3+:(Gd,Lu)2O3channel waveguide laser at 976.8 nm,” Opt. Lett.34, 2718–2720 (2009). [CrossRef]
  14. T. C. May-Smith, A. C. Muir, M. S. B. Darby, and R. W. Eason, “Design and performance of a ZnSe tetra-prism for homogeneous substrate heating using a CO2laser for pulsed laser deposition experiments,” Appl. Optics47, 1767–1780 (2008). [CrossRef]
  15. O. Pons-Y-Moll, J. Perrier, E. Millon, R. M. Defourneau, D. Defourneau, B. Vincent, A. Essahlaoui, A. Boudrioua, and W. Seiler, “Structural and optical properties of rare-earth-doped Y2O3waveguides grown by pulsed-laser deposition,” J. Appl. Phys.92, 4885–4890 (2002). [CrossRef]
  16. “Inorganic Crystal Structure Database,” http://icsd.cds.rsc.org/
  17. D. E. Zelmon, D. L. Small, and R. Page, “Refractive-index measurements of undoped yttrium aluminum garnet from 0.4 to 5.0 μm,” Appl. Opt.37(21), 4933–4935 (1998). [CrossRef]
  18. W. J. Tropf, M. E. Thomas, and E. W. Rogala, “Properties of crystals and glasses,” in Handbook of Optics, 3rd editionM. Bass, ed. (McGraw Hill Professional, 2010).
  19. S. J. Barrington, T. Bhutta, D. P. Shepherd, and R. W. Eason, “The effect of particulate density on performance of Nd:Gd3Ga5O12 waveguide lasers grown by pulsed laser deposition,” Opt. Commun.185, 145–152 (2000). [CrossRef]
  20. Y. Guyot, R. Moncorgé, L. D. Merkle, A. Pinto, B. McIntosh, and H. Verdun, “Luminescence properties of Y2O3single crystals doped with Pr3+or Tm3+and codoped with Yb3+, Tb3+or Ho3+ions,” Opt. Mater.5, 127–136 (1996). [CrossRef]
  21. A. A. Anderson, C. L. Bonner, D. P. Shepherd, R. W. Eason, C. Grivas, D. S. Gill, and N. Vainos, “Low loss (0.5 dB/cm) Nd:Gd3Ga5O12 waveguide layers grown by pulsed laser deposition,” Opt. Commun.183–186 (1997).
  22. F. S. Ermeneux, Y. Sun, R. L. Cone, R. W. Equall, R. L. Hutcheson, and R. Moncorge, “Efficient CW 2 μm Tm3+:Y2O3 Laser,” in Advanced Solid State LasersM. Fejer, H. Injeyan, and U. Keller, eds.(Optical Society of America, 1999), paper TuB8.
  23. J. R. Salcedo, J. M. Sousa, and V. V. Kuzmin, “Theoretical treatment of relaxation oscillations in quasi-three-level systems,” Appl. Phys. B62, 83–85 (1996). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.


« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited