Raman Lasers, Terahertz lasers and their applications

Raman Lasers, Terahertz lasers and their applications

Raman Lasers, Terahertz lasers and their applications


Stimulated Raman scattering (SRS) is a well-known nonlinear process, which is widely used for the frequency conversion of lasers.  Another nonlinear process that is not so widely used is stimulated Polariton scattering (SPS). These two nonlinear processes are depicted in Figure 1, where it can be seen there are strong similarities between them. In the case of SRS, the Stokes photon is retrieved, and the energy difference between pump and Stokes photons is expended as crystal vibrations. In SPS, the photon recovered emanates from a transition that is both Raman-active and infrared active, and usually lies in the far-infrared spectral region. Research at Macquarie University utilises SRS and SPS in the continuous-wave, Q-switched and ultrashort pulse regimes.


Crystalline Raman lasers

(Assoc.Prof. Helen Pask, Dr. Andrew Lee, Assoc. Prof. David Spence)

Diode-pumped Raman lasers are practical and efficient sources of laser output at otherwise "hard to reach" wavelengths. Based on diode-pumped Nd laser technology, they use stimulated Raman scattering (SRS) in nonlinear crystals to shift the output wavelength further into the infrared, with conversion efficiencies typically as high as 70%. When combined with frequency doubling, efficient conversion to the yellow-orange spectral regions, and the UV region can occur as well as the creation of devices with multi-wavelength and wavelength-selectable output.

In recent years, we have enjoyed great success in targeting the yellow-orange spectral region for medical and defence applications, and developed techniques for obtaining wavelength-selectable output across the green-yellow-red spectral region.

The main focus of our current research program is to develop efficient continuous-wave Raman lasers having unique output characteristics e.g. operating wavelength, wavelength versatility, and narrow line width, which can be used for a range of applications. Raman lasers are unique in a number of ways and the physics involved gives rise to interesting and unusual effects.  It is an understanding of this physics which has enabled us to develop such innovative laser devices and novel ways of operating them. Some research highlights are presented below. andy_lee_yellow_laser

Continuous-wave yellow Raman lasers: Our continuous-wave yellow lasers are well-suited to medical applications, particularly ophthalmology. Our best results to date are 4.3 W CW output at 586 nm, and 5.3 W CW output at 559 nm.  Higher outputs are possible at reduced duty cycle. These lasers are practical, efficient diode-pumped devices, typically pumped with up to 20 W from an 808 nm or 880 nm fibre coupled laser diode. Interesting physics includes the management of thermal, spectral broadening and competition effects. Numerical modelling in combination with experimental studies has enabled us to understand these issues, and novel resonator design has enabled us to overcome these issues. Ongoing research is aimed at improving the conversion efficiency, power scaling, device miniaturisation and demonstrating wavelength-selectable
output between blue, green, yellow and red wavelengths.

wavelength_selectableWavelength-selectable Raman lasers: Intracavity Raman lasers enable a unique visible laser technology generating wavelength-selectable output in the green-yellow spectral region. By resonating two optical fields, ie the fundamental and the first Stokes, of an intracavity Raman laser, and configuring the nonlinear crystal to phase-match a particular nonlinear interaction, we can select between the second-harmonic of the fundamental, the second harmonic of the first Stokes, and the sum frequency of these two. The optical processes can be implemented in a simple resonator with only two optical crystals (Nd vanadate and LBO/BBO), these multi-wavelength lasers can produce multi-Watt output at 532 nm, 559 nm and 586 nm. Other wavelengths combinations are possible through appropriate selection of laser and Raman crystals.

Wavelength-selectable lasers can also be made to operate efficiently at low powers (100’s of mW range), and a range of applications can be anticipated ranging from laser light shows to medicine and biomedicine. SRS is a cascading nonlinear process, and this can give rise to further outputs in the orange and red spectral regions.

Mode locked Raman lasers: We have developed a Raman technique to shift the wavelength of ultrafast lasers to new regions, and have funding for a major three-year project in collaboration with a British industry partner M Squared Lasers. We will create a new generation of wavelength-versatile ultrafast Raman lasers, built on cutting-edge pump laser technology from our partner organisation M Squared Lasers Limited. Shifting femtosecond lasers (Ti:Sapphire) and picosecond lasers (VECSELS) to new wavelength ranges such as the yellow/orange that are hard to reach by other means will permit a wider range of applications to be addressed by these standard workhorse lasers. We will create commercially viable technologies that will impact a range of scientific fields including biomedicine.

THz lasers and applications

(Dr Andrew Lee, Assoc.Prof Helen Pask, Assoc.Prof. David Spence)

THz laser output is also referred to as sub-mm wave radiation, since the typical wavelength of this radiation is around 50-500 µm. It tends to be reflected by metals, absorbed by water, and passes through many common packaging materials and clothes. Many molecular compounds have strong and distinguishable absorption bands in the THz, and thus THz has emerged as a new technology for detection of concealed drugs or explosives, for quality assurance in the pharmaceutical industry and more. Yet, there is a need for compact and affordable THz sources before these applications can become mainstream.

THz lasers: Our approach to addressing this need uses conventional solid-state Nd laser technology, and a nonlinear optical process called stimulated Polariton scattering.  A typical experimental arrangement is shown below.

THz Laser set-up

In 2014 we reported the first-ever continuous-wave, frequency-tunable intracavity MgO:LiNbO3 THz polariton laser, all previous systems having been pulsed. Moreover, this device had an exceptionally low threshold of only 2.4 W from the pump diode. Other notable progress made by PhD student Tiago Ortega has been to extend the operating range of intracavity Terahertz polariton lasers to beyond 4 THz by using rubidium titanyl phosphate (RTP) as the SPS medium. Our work on picosecond Terahertz lasers, led by A.Prof. David Spence, uses an extracavity configuration and is in its infancy, but our first contribution was published in 2015


Applications: In addition to developing THz sources, we are also applications for THz radiation, as as our sources are well-suited to both spectral fingerprinting and imaging. Specifically, we are seeking to develop applications in medicine (early stage cancer detection) and biology (determining hydration levels and overall health of plants).

Ileafmage of leaf (showing vein structure) and a paperclip taken through
an envelope using our THz source at 1.5 THz.

Our group is proactive in engaging with industry and exploring new opportunities for integration of these THz sources in devices and systems, and exploring new applications for THz radiation.

THz facilities:  Working with THz radiation requires specialised equipment. Our group occupies three state-of-the-art laser laboratories in E7B, fully equipped with laser sources and THz characterisation equipment, including Golay cells, a pyroelectric detector and a microbolometer THz camera.

Emphasis on Collaboration

In recent years we have enjoyed six productive international academic collaborations, with

  • Prof. Takashige. Omatsu and A/Prof. Katsuhiko Miyomoto (Chiba University, Japan)
  • Profs. J.Y. Wang and H. Zhang (Shandong University, China
  • Prof. Alan Kemp (Strathclyde University, UK) and student Gerald Bonner, who was jointly enrolled at Macquarie and Strathclyde.
  • Prof. Niklaus Wetter (University of Sao Paolo, Brazil
  • Prof. Y. Huo (Tsinghua University, China)
  • Prof. Gail McConnell (Strathclyde University, UK)

A notable feature of our Raman and Terahertz laser projects is the strong collaborative aspect with industry partners who have an interest in co-developing laser sources with output characteristics to match the requirements for their applications.  Devices have been developed in partnership with DSTO (Defence Science and Technology Organisation), medical laser manufacturers, and we also saw the formation of a spin-off company, Lighthouse Technologies to commercialise some of our Raman laser technology. Our current research partners include M-Squared Lasers, and Optos.

We will continue to establish collaborative links with research organisations and companies who have an interest in developing laser sources, laser applications or laser-based instrumentation, and invite expressions of interest from such organisations.

Projects for Students

Raman and Terahertz lasers are unique in a number of ways and the physics involved gives rise to interesting and unusual effects.  It is an understanding of this physics which has enabled us to develop such innovative laser devices and novel ways of operating them.  We have research projects aimed at understanding the optical field dynamics of Raman lasers, and applications of THz lasers through a combination of experimental and numerical modelling studies. Projects are available for students undertaking Masters of Research, PhD candidates and exchange scholars.

Current project offerings include:

  • Narrow linewidth Raman lasers and microlasers (contact Assoc.Prof. Helen Pask)
  • High power yellow Raman lasers (contact Assoc.Prof. Helen Pask)
  • Wavelength-versatile Raman lasers for remote sensing and biomedicine (contact Assoc.Prof. Helen Pask)
  • Diode-pumped Terahertz laser for spectral imaging and fingerprinting.(contact Dr. A. Lee)

Projects can be tailored to suit applicants strengths or particular interests (eg. theoretical, experimental, industry-related). Interested candidates should contact one of the research staff listed below. Refer also to information on scholarships.

Research Team members

Assoc. Prof. Helen Pask, ARC Future Fellow
Dr. Andrew Lee, Macquarie Vice-Chancellor’s Innovation Fellow 
Assoc. Prof. David Spence, Associate Professor of Physics
Dr. Ran Li, Postdoctoral Research Fellow
Tiago Almeida Tortega, PhD student
Yameng Zheng, PhD student


Raman lasers

  1. 1. Lee, A. J., Pask, H. M. and Omatsu, T., “A continuous-wave vortex Raman laser with sum frequency generation,” Applied Physics B, DOI :10.1007/s00340-016-6334-y (2016).
  2. 2. Kores, C.C., Jakutis-Neto, J., Geskus, D., Pask, H.M., and Wetter, N.U. "Diode-side-pumped continuous wave Nd3+: YVO4 self-Raman laser at 1176  nm," Opt. Lett. 40, 3524-3527 (2015).
  3. 3. Warrier, A.M., Lin, J.,Pask, H.M., Lee, A.J. and Spence, D.J., “Multiwavelength ultrafast LiNbO3 Raman laser,” Optics Express, vol. 23, 25582-25587 (2015).
  4. 4. Geskus, D., Jakutis-Neto, J., Pask, H.M., Wetter, N.U., “Intracavity frequency converted Raman laser producing 10 deep blue to cyan emission lines with up to 0.94 W output power”, Optics Letters, 39 (24), pp. 6799-6802, (2014).
  5. 5. Neto, J.J., Artlett, C., Lee, A., Lin, J., Spence, D., Piper, J., Wetter, N.U., Pask, H., “Investigation of blue emission from Raman-active crystals: Its origin and impact on laser performance”, Optical Materials Express, 4 (5), pp. 889-902, (2014).
  6. 6. Bonner, G.M., Lin, J., Kemp, A.J., Wang, J., Zhang, H., Spence, D.J., Pask, H.M., “Spectral broadening in continuous-wave intracavity Raman lasers”, Optics Express , 22 (7), pp. 7492-7502, (2014).
  7. Geskus, D., Neto, J.J., Reijn, S.-M., Pask, H.M., Wetter, N.U., “Quasi-continuous wave Raman lasers at 990 and 976 nm based on a three-level Nd:YLF laser”, Optics Letters, 39 (10), pp. 2982-2985, (2014).
  8. Warrier, A.M., Lin, J., Pask, H.M., Mildren, R.P.,  Coutts, D.W. and Spence,D.J.,  "Highly efficient picosecond diamond Raman laser at 1240 and 1485 nm," Opt. Express 22, 3325-3333 (2014).
  9. Lee, A.J., Omatsu, T., Pask, H.M., “Direct generation of a first-Stokes vortex laser beam from a self-Raman laser”, Optics Express, 21 (10), pp. 12401-12408, (2013.
  10. Lee, A., Pask, H.M., Spence, D.J., “Control of cascading in multiple-order Raman lasers”, Optics Letters, 37 (18), pp. 3840-3842 (2012).
  11. Spence, D.J., Li, X., Lee, A.J., Pask, H.M.,”Modeling of wavelength-selectable visible Raman lasers”,Optics Communications, 285 (18), pp. 3849-3854. (2012).
  12. Li, X., Lee, A.J., Huo, Y., Zhang, H., Wang, J., Piper, J.A., Pask, H.M., Spence, D.J.
    Managing SRS competition in a miniature visible Nd:YVO4/BaWO4 Raman laser
    Optics Express, 20 (17), pp. 19305-19312. (2012).
  13. Lin, J., Pask, H.M., “Cascaded self-Raman lasers based on 382 cm-1 shift in Nd:GdVO4”, Optics Express, 20 (14), pp. 15180-15185. (2012).
  14. Lin, J., Pask, H.M. “Nd:GdVO4 self-Raman laser using double-end polarised pumping at 880 nm for high power infrared and visible output”, Applied Physics B: Lasers and Optics, 108 (1), pp. 17-24. (2012).
  15. Omatsu, T., Okida, M., Lee, A., Pask, H.M., “Thermal lensing in a diode-end-pumped continuous-wave self-Raman Nd-doped GdVO4 laser”, Applied Physics B: Lasers and Optics, 108 (1), pp. 73-79. (2012).
  16. Jakutis-Neto, J., Lin, J., Wetter, N.U., Pask, H. “Continuous-wave watt-level Nd:YLF/KGW Raman laser operating at near-IR, yellow and lime-green wavelengths”, Optics Express, 20 (9), pp. 9841-9850, (2012).
  17. Bonner, G.M., Pask, H.M., Lee, A.J., Kemp, A.J., Wang, J., Zhang, H., Omatsu, T., “Measurement of thermal lensing in a CW BaWO4 intracavity Raman laser”, Optics Express, 20 (9), pp. 9810-9818, (2012).
  18. Lin, J., Pask, H.M., Spence, D.J., Hamilton, C.J., Malcolm, G.P.A., “Continuous-wave VECSEL Raman laser with tunable lime-yellow-orange output”,  Optics Express, 20 (5), pp. 5219-5224 (2012).
  19. Li, X., Pask, H.M., Lee, A.J., Huo, Y., Piper, J.A., Spence, D.J., “Miniature wavelength-selectable Raman laser: New insights for optimizing performance”, Optics Express, 19 (25), pp. 25623-25631. (2011).
  20. Li, X., Lee, A.J., Pask, H.M., Piper, J.A., Huo, Y., “Efficient, miniature, cw yellow source based on an intracavity frequency-doubled Nd:YVO4 self-Raman laser”, Optics Letters, 36 (8), pp. 1428-1430. (2011).
  21. Lin, J., Pask, H.M., Lee, A.J., Spence, D.J., “Study of amplitude noise in a continuous-wave intracavity frequency-doubled Raman laser”, IEEE Journal of Quantum Electronics, 47 (3), art. no. 5716916, pp. 314-319. (2011).
  22. Yu, H., Li, Z., Lee, A.J., Li, J., Zhang, H., Wang, J., Pask, H.M., Piper, J.A., Jiang, M., “A continuous wave SrMoO4 Raman laser”, Optics Letters, 36 (4), pp. 579-581. (2011).
  23. Lee, A.J., Lin, J., Pask, H.M. “Near-infrared and orange-red emission from a continuous-wave, second-Stokes self-Raman Nd:GdVO4 laser”, Optics Letters, 35 (18), pp. 3000-3002. (2010).
  24. Lee, A.J., Spence, D.J., Piper, J.A., Pask, H.M., “A wavelength-versatile, continuous-wave, self-Raman solid-state laser operating in the visible”, Optics Express, 18 (19), pp. 20013-20018 (2010).
  25. Lee, A.J., Pask, H.M., Spence, D.J., Piper, J.A., “Efficient 5.3 W cw laser at 559 nm by intracavity frequency summation of fundamental and first-Stokes wavelengths in a self-Raman Nd:GdVO4 laser”, Optics Letters, 35 (5), pp. 682-684, (2010)  [IF 3.292, 42 citations].
  26. Granados, E., Pask, H.M., Esposito, E., McConnell, G., Spence, D.J., “Multi-wavelength, all-solid-state, continuous wave mode locked picosecond Raman laser”, Optics Express, 18 (5), pp. 5289-5294. (2010).
  27. Omatsu, T., Lee, A., Pask, H.M., Piper, J., “Passively Q-switched yellow laser formed by a self-Raman composite Nd:YVO4/YVO4 crystal”, Applied Physics B: Lasers and Optics, 97 (4), pp. 799-804. (2009).
  28. Granados, E., Pask, H.M., Spence, D.J. “Synchronously pumped continuous-wave mode-locked yellow Raman laser at 559 nm”, Optics Express, 17 (2), pp. 569-574. (2009).
  29. Lee, A.J., Pask, H.M., Dekker, P., Piper, J.A., “High efficiency, multi-Watt CW yellow emission from an intracavity-doubled self-Raman laser using Nd:GdVO4”, Optics Express, 16 (26), pp. 21958-21963 (2008).
  30. Pask, H.M., Dekker, P., Mildren, R.P., Spence, D.J., Piper, J.A., “Wavelength-versatile visible and UV sources based on crystalline Raman lasers”, Progress in Quantum Electronics, 32 (3-4), pp. 121-158. (2008).  [INVITED PAPER]
  31. Pask, H.M., Mildren, R.P., Piper, J.A., “Optical field dynamics in a wavelength-versatile, all-solid-state intracavity cascaded pulsed Raman laser”, Applied Physics B: Lasers and Optics, 93 (2-3), pp. 507-513. (2008).
  32. Lee, A.J., Pask, H.M., Omatsu, T., Dekker, P., Piper, J.A., “All-solid-state continuous-wave yellow laser based on intracavity frequency-doubled self-Raman laser action”, Applied Physics B: Lasers and Optics, 88 (4), pp. 539-544. (2007).
  33. Dekker, P., Pask, H.M., Spence, D.J., Piper, J.A., “Continuous-wave, intracavity doubled, self-Raman laser operation in Nd:GdVO4  at 586.5 nm”, Optics Express, 15 (11), pp. 7038-7046. (2007).
  34. Piper, J.A., Pask, H.M., “Crystalline Raman lasers”, IEEE Journal on Selected Topics in Quantum Electronics, 13 (3), pp. 692-704. (2007).  [INVITED PAPER]
  35. Spence, D.J., Dekker, P., Pask, H.M., “Modeling of continuous wave intracavity Raman lasers”, IEEE Journal on Selected Topics in Quantum Electronics, 13 (3), pp. 756-763. (2007).
  36. Dekker, P., Pask, H.M., Piper, J.A., “All-solid-state 704 mW continuous-wave yellow source based on an intracavity, frequency-doubled crystalline Raman laser”, Optics Letters, 32 (9), pp. 1114-1116. (2007).
  37. Pask, H.M., “Continuous-wave, all-solid-state, intracavity Raman laser”, Optics Letters, 30 (18), pp. 2454-2456. (2005)  [highlighted by Photonics Spectra trade magazine article “Intracavity Raman Laser is Continuous-Wave” by Breck Hitz in November 2005].
  38. Johnson, K.S., Pask, H.M., Withford, M.J., Coutts, D.W., “Efficient all-solid-state Ce:LiLuF laser source at 309 nm”, Optics Communications, 252 (1-3), pp. 132-137. (2005).
  39. Mildren, R.P., Pask, H.M., Piper, J.A., “Raman lasers offer power and wavelength versatility”, Photonics Spectra, 39 (7), pp. 52-59. (2005). [INVITED PAPER]
  40. Mildren, R.P., Pask, H.M., Ogilvy, H., Piper, J.A., “Discretely tunable, all-solid-state laser in the green, yellow, and red”, Optics Letters, 30 (12), pp. 1500-1502 (2005).
  41. Ogilvy, H., Pask, H.M., Piper, J.A., Omatsu, T., “Efficient frequency extension of a diode-side-pumped Nd:YAG laser by intracavity SRS in crystalline materials”, Optics Communications, 242 (4-6), pp. 575-579. (2004).
  42. Mildren, R.P., Convery, M., Pask, H.M., Piper, J.A., Mckay, T., “Efficient, all-solid-state, Raman laser in the yellow, orange and red”, Optics Express, 12 (5), pp. 785-790. (2004).
  43. Omatsu, T., Ojima, Y., Pask, H.M., Piper, J.A., Dekker, P., “Efficient 1181 nm self-stimulating Raman output from transversely diode-pumped Nd3+:KGd(WO4)2 laser”, Optics Communications, 232 (1-6), pp. 327-331. (2004).
  44. Simons, J., Pask, H., Dekker, P., Piper, J., “Small-scale, all-solid-state, frequency-doubled intracavity Raman laser producing 5 m W yellow-orange output at 598 nm”,  Optics Communications, 229 (1-6), pp. 305-310. (2004).
  45. Pask, H.M., “The design and operation of solid-state Raman lasers”, Progress in Quantum Electronics, 27 (1), pp. 3-56. (2003), [INVITED PAPER]
  46. Pask, H.M., Myers, S., Piper, J.A., Richards, J., McKay, T., “High average power, all-solid-state external resonator Raman laser”, Optics Letters, 28 (6), pp. 435-437 (2003).
  47. Pask, H.M., Piper, J.A., “Diode-pumped LiIO3 intracavity Raman lasers”, IEEE Journal of Quantum Electronics, 36 (8), pp. 949-955 (2000).
  48. Pask, H.M., Piper, J.A., “Efficient all-solid-state yellow laser source producing 1.2-W average power”, Optics Letters, 24 (21), pp. 1490-1492 (1999).
  49. Blows, J.L., Omatsu, T., Dawes, J., Pask, H., Tateda, M., “Heat generation in Nd:YVO4 with and without laser action”, IEEE Photonics Technology Letters, 10 (12), pp. 1727-1729 (1998).
  50. Pask, H.M., Piper, J.A., “Practical 580 nm source based on frequency doubling of an intracavity-Raman-shifted Nd:YAG laser”, Optics Communications, 148 (4-6), pp. 285-288 (1998).
  51. Lee, A.J., Zhang, C., Omatsu, T., Pask, H.M., “An intracavity, frequency-doubled self-raman vortex laser”, Optics Express, 22 (5), pp. 5400-5409, (2014).

Terahertz lasers

  1. Lee, A.J. and Pask, H.M., "Cascaded stimulated polariton scattering in a Mg:LiNbO3 terahertz laser," Opt. Express 23, 8687-8698 (2015).
  2. Warrier, A.M., Lin, J.,Pask, H.M., Lee, A.J. and Spence, D.J., “Multiwavelength ultrafast LiNbO3 Raman laser,” Optics Express, vol. 23, 25582-25587 (2015).
  3. T. Ortega, H. M. Pask, D. Spence, and A. Lee, "Competition Effects Between Stimulated Raman and Polariton Scattering in Intracavity KTiOPO4 Crystal," in Advanced Solid State Lasers, OSA Technical Digest (online) (Optical Society of America, 2015), paper ATu3A.3. (awarded Best Student Paper and a $1000 prize).  ISBN: 978-1-943580-02-6.
  4. Lee, A.J. and Pask, H.M., "Continuous wave, frequency-tunable terahertz laser radiation generated via stimulated polariton scattering," Optics Letters, 39 (3), pp. 442-445 (2014).
  5. A.J. Lee and H. M. Pask, "Pyroelectric effects in MgO:LiNbO3 and its influence on  THz generation in a polariton laser," in Advanced Solid State Lasers, OSA Technical Digest (online) (Optical Society of America, 2014), paper ATh2A (2014).  ISBN: 978-1-55752-822-3.
  6. Lee, A.J. and Pask, H.M., "A continuous-wave, solid-state stimulated polariton THz source," Lasers and   Electro-Optics Europe (CLEO EUROPE/IQEC), 2013 Conference on and   International Quantum Electronics Conference , 12-16 May,  paper SA1_4 (2013). ISBN: 978-1-4673-6475-1.
  7. Lee, A.J., Pask, H.M., “A diode-end-pumped frequency-tunable THz source with very low threshold”, International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, art. no. 6379511, (2012).  ISBN:978-1-4673-1598-2 [INVITED PAPER]
  8. H. Pask, Y. He, and A. Lee, "Diode-pumped Terahertz laser source based on stimulated polariton scattering," in CLEO/Europe and EQEC 2011 Conference Digest, OSA Technical Digest (CD) (Optical Society of America, 2011), paper CC_P12. P12, (2011).   ISBN: 978-1-4577-0532-8.
  9. Lee, A., He, Y., Pask, H., “Frequency-tunable THz source based on stimulated polariton scattering in Mg:LiNbO3”, IEEE Journal of Quantum Electronics, 49 (3), art. no. 6451099, pp. 357-364. (2013).
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