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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 12 — Jun. 11, 2007
  • pp: 7616–7622
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Direct generation of high power Laguerre-Gaussian output from a diode-pumped Nd:YVO4 1.3-μm bounce laser

Masahito Okida, Takashige Omatsu, Masahide Itoh, and Toyohiko Yatagai  »View Author Affiliations


Optics Express, Vol. 15, Issue 12, pp. 7616-7622 (2007)
http://dx.doi.org/10.1364/OE.15.007616


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Abstract

We demonstrate direct production of a high power Laguerre–Gaussian mode from a diode-pumped Nd:YVO4 1.3-μm bounce amplifier with an asymmetric cavity configuration. A maximum LG output of 7.7 W is obtained.

© 2007 Optical Society of America

1. Introduction

The Laguerre–Gaussian (LG) beam is an eigen mode of the paraxial propagation electromagnetic equation and has received attention recently for possible use in various applications including optical manipulation and material processing, because of its orbital angular momentum arising from an on-axial phase singularity (optical vortex) [1–3

1. L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, “Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes,” Phys. Rev. A 45, 8185–8189 (1992) [CrossRef] [PubMed]

]. An LG beam, having an annular spatial form in the far-field, can also be useful for super-resolution microscopes based on stimulated emission and up-conversion fluorescence depletion [4–6

4. T. Watanabe, Y Igasaki, N. Fukuchi, M. Sakai, S. Ishiuchi, M. Fujii, T. Omatsu, K. Yamamoto, and Y. Iketaki, “Formation of a doughnut laser beam for super-resolving microscopy using a phase spatial light modulato,” Opt. Eng. 43, 1136–1143 (2004) [CrossRef]

]. A hologram or spatial light modulator (SLM) is typically used to produce an LG beam [7

7. N. R. Heckenberg, R. McDuff, C. P. Smith, and A. G. White, “Generation of optical phase singularities by computer-generated holograms,” Opt. Lett. 17, 221–223 (1992) [CrossRef] [PubMed]

]. However, these methods involve significant wastage of beam power, since only about 30% of the energy of the incident Gaussian beam is converted into the LG beam. The output power is also limited by the low damage threshold of holograms and SLMs. Direct production of LG modes has been demonstrated using a laser cavity by placing phase elements or special mirrors inside the resonator [8

8. R. Oron, Y. Danziger, N. Davidson, A. A. Friesem, and E. Hasman, “Laser mode discrimination with intra-cavity spiral phase elements,” Opt. Commun. 169, 115–121 (1999) [CrossRef]

, 9

9. T. Moser, M. A. Ahmed, F. Pigeon, O. Parriaux, E. Wyss, and Th. Graf, “Generation of radially polarized beams in Nd:YAG lasers with polarization selective mirrors,” Laser Phys. Lett. 1, 234–236 (2004) [CrossRef]

]. However, the output power achieved is mostly limited, because insertion of additional elements inside the resonator causes severe internal loss in the laser cavity. Recently, Chen et al. have demonstrated a direct generation of LG output from an end-diode-pumped Nd:YVO4 laser by using a doughnut shaped pumping [10

10. Y. F. Chen and Y. P. Lan, “Dynamics of the Laguerre Gaussian TEM0,l mode in a solid-state laser,” Phys. Rev. A 63, 063807 (2001) [CrossRef]

,11

11. J.-F. Bisson, Yu. Senatsky, and Ken-Ichi Ueda, “Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping,” Laser Phys. Lett. 2, 327–333 (2005) [CrossRef]

]. They did not mention quantitatively the laser performances including the output power and optical efficiency, and neither they did address 1.3-μm laser action.

Side-pumped bounce amplifiers, in which a very high inversion population density is produced near the pump face, have generated high power output at 1.06 μm and 1.3 μm [12–14

12. J. E. Bernard and A. J. Alcock, “High-efficiency diode-pumped Nd: YVO4 slab laser” Opt. Lett. 18, 968–970 (1993) [CrossRef] [PubMed]

]. These amplifiers can also be used to generate high quality output using an asymmetric resonator approach based on the power dependence of the thermal lens [15

15. A. Minassian, B. Thompson, and M. J. Damzen, “Ultrahigh-efficiency TEM00 diode-side-pumped Nd:YVO4 laser,” Appl. Phys. B 76, 341–343 (2003) [CrossRef]

].

In this paper, we present the first demonstration, to the best of our knowledge, of the direct production of a high power (> 7 W) 1.3-μm LG mode from a diode-pumped Nd:YVO4 bounce amplifier with an asymmetric cavity configuration. This system does not require any additional phase elements, such as a hologram or a phase plate, to produce LG modes. It is based on the formation of a limiting aperture for the desired LG mode in the gain medium by utilizing power-dependent thermal lensing of the laser material. High power 1.3-μm LG lasers will open up new applications in optical manipulation due to their low absorption and scattering loss in water.

2. Experiment

Figure 1 shows a schematic diagram of a laser cavity. The amplifier used in the current study was a 1-at.% Nd-doped a-cut YVO4 slab with dimensions 2 mm × 5 mm × 20 mm. The pump diode was a 55-W CW diode bar array. The output of the diode was focused by a cylindrical lens to be a line with dimensions 0.2 mm × 18 mm on the pump face. The cavity was formed by a high reflection flat mirror and an 85% reflective flat output coupler, to give a wavelength of 1.3 μm. To achieve good spatial overlap between the pumped region and laser mode, two cylindrical lenses (f = 50 mm) were placed inside the cavity. The internal bounce angle with respect to the pump surface of the amplifier was ∼ 10°.

Fig. 1. Experimental setup of a laser system with a symmetric cavity. EM, and OC are a high-reflection flat mirror and a 85 % reflection output coupler, respectively. VCLs are vertical cylindrical lenses.

The cavity was compact and symmetric with respect to the position of the Nd:YVO4 amplifier, making the cavity stable at all pump levels. Its length was 160 mm (L1 = L2 = 80 mm). The output exhibited a typical multi-mode profile, as shown in Fig. 2(a), and its power reached 11.2 W at maximum pump level (Fig. 2(b)).

Fig. 2. (a) Spatial form of the output from the symmetric cavity. (b) Experimental plots of output power as a function of pump power.

To improve the beam quality, the cavity was lengthened on both sides to be slightly asymmetric with respect to the position of the Nd:YVO4 amplifier, as shown in Fig. 3. The total cavity length was 380 mm with L1 = 180 mm and L2 = 200 mm. Below a pump power of 40 W, the cavity was stable and the laser output showed a mixed-mode (a mixture of Hermite–Gaussian HG00 and HG01 modes) profile in the far-field. Above this pump level, the laser started to produce the HG01 mode (Fig. 4(a)). We carefully re-adjusted the cylindrical lens pair and cavity mirrors, after which the laser operated in a ‘doughnut’ mode with an annular intensity profile, as shown in Fig. 4(b).

Fig. 3. Schematic diagram of a laser system with an asymmetric cavity

To confirm that the laser output beam contains a phase singularity, we analyzed the wavefront of the output by interferometric fringes. Figure 4(c) shows fringes formed by the laser output beam and a copy of itself. The laser output exhibits an on-axial phase singularity. Fringes formed by the laser output and a spherical reference beam have a single-arm spiral, as shown in Fig. 4(d). These results indicate that the laser operates in the LG01 mode. Figure 5 shows experimental plots of the LG01 output power as a function of the pump power. A maximum output power of 7.7 W was obtained at a pump power of 54 W. A corresponding optical efficiency of 14 % was achieved.

Fig. 4. Spatial forms of (a) HG01 and (b) LG beams. (c) Observed fringes formed by the LG beam and a copy of itself. (d) Fringes formed by the LG and spherical reference beams.
Fig. 5. Output powers of HG01 and LG01 modes

3. Discussion

3.1 HG01 mode discrimination due to thermal lensing in a diode-side-pumped bounce laser

Fig. 6. Numerical simulation of phase distribution in an amplifier with 1342-nm lasing at 40-W pumping. The red and blue parabolic curves show the thermal lensing experienced in the amplifier for the HG00 and HG01 modes.

We numerically simulated the horizontal thermal lens powers by using the conventional heat diffusion equation [16

16. J. C. Bermudez G., M. J. Damzen, V. J. Pinto-Robledo, A. V. Kir’yanov, and J. J. Soto-Bernal, “Compact diode-side-pumped Nd:YVO4 laser in grazing-incidence configuration”, Appl. Phys. B 76, 13–16 (2003) [CrossRef]

] and the heat loading formula in 1.3-μm lasers proposed previously by our group [17

17. M. Okida, M. Itoh, T. Yatagai, H. Ogilby, J. Piper, and T. Omatsu, “Heat generation in Nd doped vanadate crystals with 1.34 μm laser action,” Opt. Express 13, 4909–4915 (2005) [CrossRef] [PubMed]

,18

18. M. Okida, A. Tonouchi, M. Itoh, T. Yatagai, and T. Omatsu, “Thermal-lens measurement in a side-pumped 1.3 μm Nd:YVO4 bounce laser”, Opt. Commun. (in press)

]. At a pump power of 40 W, the HG00 mode experiences a 5.2-m-1 horizontal thermal lens, estimated from a parabolic fit curve to the simulated phase distribution within an effective HG00 mode size (2.4 mm) in the amplifier. When the cavity length is extended to L2 = 200 mm and made asymmetric with respect to the position of the slab amplifier, the horizontal thermal lens makes the cavity unstable and suppresses the HG00 mode operation. Meanwhile the HG01 mode experiences a horizontal thermal lens with a power of 3.8–4.0 m-1 within a pump power range of 40–50 W, and the laser can maintain the HG01 mode (Fig. 5). These simulations demonstrate that the horizontal thermal lens showing transverse-mode-dependence contributes mainly to the unexpected HG01 mode operation.

3.2 Mode conversion from HG modes to LG modes in a diode-side-pumped bounce laser

Although the physics of HG–LG mode conversion in a bounce laser is not fully understood, we believe that a bounce laser cavity can be used to create an HG–LG mode converter by utilizing the thermal lens in the amplifier and a cylindrical lens pair inside the cavity. A schematic model of a bounce cavity is shown in Fig. 7.

Fig. 6. Mode propagation inside a resonator. TL is the horizontal thermal lens.

In the vertical plane, a con-focal cylindrical lens pair placed inside the cavity cancels the vertical thermal lens and causes a 2π Gouy phase shift in the cavity HG10 mode traveling from the EM to the OC. In the horizontal plane, where there is no cylindrical lens pair, a Gouy phase of the cavity mode is determined by the horizontal thermal lens. A wavefront of the HG01 mode experiences a Gouy phase shift of π while traveling from the EM to the OC. Consequently, there is a Gouy phase difference of π/2 between the vertical and horizontal modes while traveling from the amplifier to the OC (a half-way trip of the cavity). When the HG01 and HG10 modes are allowed to oscillate, the cavity operates in the LG01 mode.

4. Conclusion

We have demonstrated direct production of a high power 1.3-μm LG mode from a diode-pumped Nd:YVO4 bounce amplifier with an asymmetrically extended cavity. A maximum output power of 7.7 W was obtained for a pump power of 54 W. High power 1.3-μm LG lasers, exhibiting low absorption and scattering loss for propagation in water, have potential uses in various applications, such as in optical manipulation. The laser presented in this paper can be extended to generate highly intense pulses by Q-switching as well as mode-locking techniques and offers the possibility of the production of high power optical vortexes in the visible and ultra-violet regimes.

Acknowledgments

The authors acknowledge support from a scientific research grant-in-aid from the Ministry of Education, Science and Culture of Japan and the Japan Society for the Promotion of Science.

References and links

1.

L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, “Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes,” Phys. Rev. A 45, 8185–8189 (1992) [CrossRef] [PubMed]

2.

A. T. O’Neil, I. MacVicar, L. Allen, and M. J. Padgett, “Intrinsic and Extrinsic Nature of the Orbital Angular Momentum of a Light Beam,” Phys. Rev. Lett. 88, 053601 (2002) [CrossRef] [PubMed]

3.

K. Sueda, G. Miyaji, N. Miyanaga, and M. Nakatsuka, “Laguerre-Gaussian beam generated with a multilevel spiral phase plate for high intensity laser pulses,” Opt. Express 12, 3548–3553 (2004) [CrossRef] [PubMed]

4.

T. Watanabe, Y Igasaki, N. Fukuchi, M. Sakai, S. Ishiuchi, M. Fujii, T. Omatsu, K. Yamamoto, and Y. Iketaki, “Formation of a doughnut laser beam for super-resolving microscopy using a phase spatial light modulato,” Opt. Eng. 43, 1136–1143 (2004) [CrossRef]

5.

T. Watanabe, Y. Iketaki, T. Omatsu, K. Yamamoto, S. Ishiuchi, M. Sakai, and M. Fujii, “Two-color far-field super-resolution microscope using a doughnut beam,” Chem. Phys. Lett. 371, 634–639 (2003) [CrossRef]

6.

T. Watanabe, Y. Iketaki, T. Omatsu, K. Yamamoto, M. Sakai, and M. Fujii, “Two-point-separation in super-resolution fluorescence microscope based on up-conversion fluorescence depletion technique,” Opt. Express 11, 3271–3276 (2003). [CrossRef] [PubMed]

7.

N. R. Heckenberg, R. McDuff, C. P. Smith, and A. G. White, “Generation of optical phase singularities by computer-generated holograms,” Opt. Lett. 17, 221–223 (1992) [CrossRef] [PubMed]

8.

R. Oron, Y. Danziger, N. Davidson, A. A. Friesem, and E. Hasman, “Laser mode discrimination with intra-cavity spiral phase elements,” Opt. Commun. 169, 115–121 (1999) [CrossRef]

9.

T. Moser, M. A. Ahmed, F. Pigeon, O. Parriaux, E. Wyss, and Th. Graf, “Generation of radially polarized beams in Nd:YAG lasers with polarization selective mirrors,” Laser Phys. Lett. 1, 234–236 (2004) [CrossRef]

10.

Y. F. Chen and Y. P. Lan, “Dynamics of the Laguerre Gaussian TEM0,l mode in a solid-state laser,” Phys. Rev. A 63, 063807 (2001) [CrossRef]

11.

J.-F. Bisson, Yu. Senatsky, and Ken-Ichi Ueda, “Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping,” Laser Phys. Lett. 2, 327–333 (2005) [CrossRef]

12.

J. E. Bernard and A. J. Alcock, “High-efficiency diode-pumped Nd: YVO4 slab laser” Opt. Lett. 18, 968–970 (1993) [CrossRef] [PubMed]

13.

A. Minassian and M. J. Damzen, “20 W bounce geometry diode-pumped Nd:YVO4 laser system at 1342 nm,” Opt. Commun. 230, 191–195 (2004) [CrossRef]

14.

A. Minassian, B. Thompson, and M. J. Damzen, “High-power TEM00 grazing-incidence Nd:YVO4 oscillators in single and multiple bounce configurations,” Opt. Commun. 245, 295–300 (2005) [CrossRef]

15.

A. Minassian, B. Thompson, and M. J. Damzen, “Ultrahigh-efficiency TEM00 diode-side-pumped Nd:YVO4 laser,” Appl. Phys. B 76, 341–343 (2003) [CrossRef]

16.

J. C. Bermudez G., M. J. Damzen, V. J. Pinto-Robledo, A. V. Kir’yanov, and J. J. Soto-Bernal, “Compact diode-side-pumped Nd:YVO4 laser in grazing-incidence configuration”, Appl. Phys. B 76, 13–16 (2003) [CrossRef]

17.

M. Okida, M. Itoh, T. Yatagai, H. Ogilby, J. Piper, and T. Omatsu, “Heat generation in Nd doped vanadate crystals with 1.34 μm laser action,” Opt. Express 13, 4909–4915 (2005) [CrossRef] [PubMed]

18.

M. Okida, A. Tonouchi, M. Itoh, T. Yatagai, and T. Omatsu, “Thermal-lens measurement in a side-pumped 1.3 μm Nd:YVO4 bounce laser”, Opt. Commun. (in press)

OCIS Codes
(140.3480) Lasers and laser optics : Lasers, diode-pumped
(140.4780) Lasers and laser optics : Optical resonators
(140.6810) Lasers and laser optics : Thermal effects

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: April 17, 2007
Revised Manuscript: June 4, 2007
Manuscript Accepted: June 4, 2007
Published: June 6, 2007

Citation
Masahito Okida, Takashige Omatsu, Masahide Itoh, and Toyohiko Yatagai, "Direct generation of high power Laguerre–Gaussian output from a diode-pumped Nd:YVO4 1.3-μm bounce laser," Opt. Express 15, 7616-7622 (2007)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-15-12-7616


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References

  1. L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, "Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes," Phys. Rev. A 45, 8185-8189 (1992) [CrossRef] [PubMed]
  2. A. T. O'Neil, I. MacVicar, L. Allen, and M. J. Padgett, "Intrinsic and Extrinsic Nature of the Orbital Angular Momentum of a Light Beam," Phys. Rev. Lett. 88, 053601 (2002) [CrossRef] [PubMed]
  3. K. Sueda, G. Miyaji, N. Miyanaga, and M. Nakatsuka, "Laguerre-Gaussian beam generated with a multilevel spiral phase plate for high intensity laser pulses," Opt. Express 12, 3548-3553 (2004) [CrossRef] [PubMed]
  4. T. Watanabe, Y Igasaki, N. Fukuchi, M. Sakai, S. Ishiuchi, M. Fujii, T. Omatsu, K. Yamamoto, and Y. Iketaki, "Formation of a doughnut laser beam for super-resolving microscopy using a phase spatial light modulato," Opt. Eng. 43, 1136-1143 (2004) [CrossRef]
  5. T. Watanabe, Y. Iketaki, T. Omatsu, K. Yamamoto, S. Ishiuchi, M. Sakai, and M. Fujii, "Two-color far-field super-resolution microscope using a doughnut beam," Chem. Phys. Lett. 371, 634-639 (2003) [CrossRef]
  6. T. Watanabe, Y. Iketaki, T. Omatsu, K. Yamamoto, M. Sakai, and M. Fujii, "Two-point-separation in super-resolution fluorescence microscope based on up-conversion fluorescence depletion technique," Opt. Express 11, 3271-3276 (2003). [CrossRef] [PubMed]
  7. N. R. Heckenberg, R. McDuff, C. P. Smith, and A. G. White, "Generation of optical phase singularities by computer-generated holograms," Opt. Lett. 17, 221-223 (1992) [CrossRef] [PubMed]
  8. R. Oron, Y. Danziger, N. Davidson, A. A. Friesem, and E. Hasman, "Laser mode discrimination with intra-cavity spiral phase elements," Opt. Commun. 169, 115-121 (1999) [CrossRef]
  9. T. Moser, M. A. Ahmed, F. Pigeon, O. Parriaux, E. Wyss, and Th. Graf, "Generation of radially polarized beams in Nd:YAG lasers with polarization selective mirrors," Laser Phys. Lett. 1, 234-236 (2004) [CrossRef]
  10. Y. F. Chen and Y. P. Lan, "Dynamics of the Laguerre Gaussian TEM0,l mode in a solid-state laser," Phys. Rev. A 63, 063807 (2001) [CrossRef]
  11. J.-F. Bisson, Yu. Senatsky, and Ken-Ichi Ueda, "Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping," Laser Phys. Lett. 2, 327-333 (2005) [CrossRef]
  12. J. E. Bernard and A. J. Alcock, "High-efficiency diode-pumped Nd: YVO4 slab laser," Opt. Lett. 18, 968-970 (1993) [CrossRef] [PubMed]
  13. A. Minassian and M. J. Damzen, "20 W bounce geometry diode-pumped Nd:YVO4 laser system at 1342 nm," Opt. Commun. 230,191-195 (2004) [CrossRef]
  14. A. Minassian, B. Thompson and M. J. Damzen, "High-power TEM00 grazing-incidence Nd:YVO4 oscillators in single and multiple bounce configurations," Opt. Commun. 245, 295-300 (2005) [CrossRef]
  15. A. Minassian, B. Thompson and M. J. Damzen, "Ultrahigh-efficiency TEM00 diode-side-pumped Nd:YVO4 laser," Appl. Phys. B 76, 341-343 (2003) [CrossRef]
  16. J. C. Bermudez G., M. J. Damzen V. J. Pinto-Robledo, A. V. Kir’yanov, and J. J. Soto-Bernal, "Compact diode-side-pumped Nd:YVO4 laser in grazing-incidence configuration," Appl. Phys. B 76, 13-16 (2003) [CrossRef]
  17. M. Okida, M. Itoh, T. Yatagai, H. Ogilby, J. Piper, and T. Omatsu, "Heat generation in Nd doped vanadate crystals with 1.34 μm laser action," Opt. Express 13, 4909-4915 (2005) [CrossRef] [PubMed]
  18. M. Okida, A. Tonouchi, M. Itoh, T. Yatagai, and T. Omatsu, "Thermal-lens measurement in a side-pumped 1.3 μm Nd:YVO4 bounce laser," Opt. Commun. (in press)

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