Efficient Trichromatic Nd:YLF Laser Emitting at 1047 nm, 1053 nm and 1314 nm

Round 1

Reviewer 1 Report

The authors experimentally demonstrated triple-wavelength emission in a Nd:YLF crystal at 1047 nm, 1053 nm, and 1314 nm pumped at 797 nm. It is stated that this work is the first report of triple-wavelength emission in a Nd:YLF crystal. Different combinations of laser wavelengths were achieved by system adjusting. Each wavelength operation could be selected by simple cavity alignment .Spectra of one-color, two-color, and three-color lasing were measured. The implemented design allowed to reach efficiencies above 31% for all wavelength operations, achieving record values for slope- and optical-to-optical efficiency at 1314 nm with 797 nm pumping. The maximum output powers have sub-kW level. Beam quality (M^2 ~ 2.2…4.2) was also measured. I believe that the paper has sufficient novelty and the reported results are solid. I have the following comments and suggestions for the authors.

1. The authors demonstrated laser operation at different energy transitions. So, I suggest to add a scheme of energy levels for Nd3+ ions.

2. Please comment the system stability and power fluctuation for each operating mode. 

3. There are typos, for example: line 189: 053 nm -> 1053 nm.

Author Response

We would also like to thank the reviewers for their thorough revision of our manuscript and for all the comments and suggestions that improved the overall quality of this work.

Here we cover all the reviewer’s comments and suggestions, point by point, while identifying the paragraphs and sections of the manuscript in which the changes were made.

Editor suggestions

The total word count excluding references is now above 4000. Also, throughout the article we are discussing the results and comparing with other works.

Review 1

The authors experimentally demonstrated triple-wavelength emission in a Nd:YLF crystal at 1047 nm, 1053 nm, and 1314 nm pumped at 797 nm. It is stated that this work is the first report of triple-wavelength emission in a Nd:YLF crystal. Different combinations of laser wavelengths were achieved by system adjusting. Each wavelength operation could be selected by simple cavity alignment. Spectra of one-color, two-color, and three-color lasing were measured. The implemented design allowed to reach efficiencies above 31% for all wavelength operations, achieving record values for slope- and optical-to-optical efficiency at 1314 nm with 797 nm pumping. The maximum output powers have sub-kW level. Beam quality (M^2 ~ 2.2…4.2) was also measured. I believe that the paper has sufficient novelty and the reported results are solid. I have the following comments and suggestions for the authors.

1. The authors demonstrated laser operation at different energy transitions. So, I suggest to add a scheme of energy levels for Nd3+ ions.

R: We have incorporated Figure 1B into the manuscript, illustrating the energy transitions of the Nd:YLF crystal.

2. Please comment the system stability and power fluctuation for each operating mode.

R: After Table 2, we have provided a concise discussion regarding power fluctuation and its influence on the standard deviation of the measured values. The errors of the peak output power, shown in table 2, already incorporate the long term (different measurements during approximately 3 weeks) fluctuations.

3. There are typos, for example: line 189: 053 nm -> 1053 nm.

R: The typo was corrected, and the manuscript underwent a meticulous review.

Review 2

In the manuscript ' Efficient Trichromatic Nd:YLF Laser Emitting at 1047 nm, 1053 nm and 1314 nm ,' the authors Prado et al reported a Nd:YLF laser operating at 1047 nm, 1053 nm and 1314 nm using a diode-stack at 797 nm and a side-pumped structure. The high efficiency and power as well as the multi-wavelength operation have shown a great promise in applications. The manuscript can be accepted as the publication of Photonics after the following questions are answered.

1. The authors just described the focal length of the lens in the laser while no mentioning the designed mode size in the crystal. Therefore, the authors are encouraged to estimate the overlap efficiency and absorption efficiency of the laser.

R: We have supplemented the description with information about the focusing of the diode (measured spot size) and have compared it with the simulated mode size in the crystal. We used a MatLab script to calculate spectral overlap by convolution of the pump diode's emission curve with the Nd:YLF crystal's absorption spectrum. At a depth of 5.75 mm, absorption exceeds 97%. The effective absorption coefficient was used for calculating the overall overlap efficiency, as per Equation 1, resulting in an overlap efficiency of 98.3%.

2. The authors just mentioned their laser is promising in Q-switching operation while the current M2 is a little high to achieve this, as the mode size on the saturable absorbers should be smaller. How will the authors improve the system to achieve the Q-switching operation using saturable absorbers?

R: While the improvement of M² during Q-switching does occur (beam clean-up effect) and is important, in our experience with similar high-power pumped systems, very efficient Q-switched pulses can be generated with an M² much worse than the ones measured for this laser. For example, in our work [Prado, F.M.; Franco, T.J.; Wetter, N.U. Sub-Nanosecond, 41 MJ Pulse Energy, Passively Q-Switched Nd:YLF Laser. Opt. Laser Technol. 2023, 162, 109257, doi:10.1016/j.optlastec.2023.109257], we showcased a Q-switched Nd:YLF laser with an M²~6 that generated 41 mJ single pulse energy, with a peak power of 46 MW. One thing that is important to note is that the M² value of ~6 was generated after the beam clean-up effect, indicating a much higher M² during the QCW laser emission.

Other works also showcased Q-switched pulse generation with M2 close to 8 for Cr:YAG/Nd:YAG [Q. Yang, J. Ma, T. Lu, X. Ma, X. Zhu, 160mJ and 9ns electro-optics Q-switched conductively cooled 1047nm Nd:YLF laser, in: XX Int. Symp. High-Power Laser Syst. Appl. 2014, SPIE (2015), 64-73. DOI: https://doi.org/10.1117/12.2064316] and even an M2 of 9 for a Q-switched Nd:YAG laser with 53 mJ of pulse energy [K. Lee, H.C. Lee, J.Y. Cho, J.C. Lee, J. Yi, Passively Q-switched, high peak power Nd:YAG laser pumped by QCW diode laser, Opt. Laser Technol. 44 (7) (2012) 2053–2057, https://doi.org/10.1016/j.optlastec.2012.03.027].

3. In the introduction, another Nd-doped laser Nd:LuAG was not mentioned and the authors are encouraged to reference this laser like following:
4. Zhang, T. Liu, Y. Shen, C. Zhao, B. Huang, Z. Kang, G. Qin, Q. Liu, and X. Fu, “ 516 mW, nanosecond Nd:LuAG laser Q-switched by gold nanorods, ” Chin. Opt. Lett. 16, 030011 (2018).

R: We have included Nd:LuAG as one of the notable Nd-doped crystals, and have also referenced the paper indicated by the reviewer.

Reviewer 2 Report

In the manuscript ' Efficient Trichromatic Nd:YLF Laser Emitting at 1047 nm, 1053 nm and 1314 nm ,' the authors Prado et al reported a Nd:YLF laser operating at 1047 nm, 1053 nm and 1314 nm using a diode-stack at 797 nm and a side-pumped structure. The high efficiency and power as well as the multi-wavelength operation have shown a great promise in applications. The manuscript can be accept as the publication of Photonics after the following questions are answered.

1. The authors just described the focal length of the lens in the laser while no mentioning the designed mode size in the crystal. Therefore, the authors are encouraged to estimate the overlap efficiency and absorption efficiency of the laser. 

2. The authors just mentioned their laser is promising in Q-switching operation while the current M2 is a little high to achieve this, as the mode size on the saturable absorbers should be smaller. How will the authors improve the system to achieve the Q-switching operation using saturable absorbers?

3. In the introduction, another Nd-doped laser Nd:LuAG was not mentioned and the authors are encouraged to reference this laser like following :

G. Zhang, T. Liu, Y. Shen, C. Zhao, B. Huang, Z. Kang, G. Qin, Q. Liu, and X. Fu, “ 516 mW, nanosecond Nd:LuAG laser Q-switched by gold nanorods, ” Chin. Opt. Lett. 16, 030011 (2018).

Author Response

We would also like to thank the reviewers for their thorough revision of our manuscript and for all the comments and suggestions that improved the overall quality of this work.

Here we cover all the reviewer’s comments and suggestions, point by point, while identifying the paragraphs and sections of the manuscript in which the changes were made.

Editor suggestions

The total word count excluding references is now above 4000. Also, throughout the article we are discussing the results and comparing with other works.

Review 1

The authors experimentally demonstrated triple-wavelength emission in a Nd:YLF crystal at 1047 nm, 1053 nm, and 1314 nm pumped at 797 nm. It is stated that this work is the first report of triple-wavelength emission in a Nd:YLF crystal. Different combinations of laser wavelengths were achieved by system adjusting. Each wavelength operation could be selected by simple cavity alignment. Spectra of one-color, two-color, and three-color lasing were measured. The implemented design allowed to reach efficiencies above 31% for all wavelength operations, achieving record values for slope- and optical-to-optical efficiency at 1314 nm with 797 nm pumping. The maximum output powers have sub-kW level. Beam quality (M^2 ~ 2.2…4.2) was also measured. I believe that the paper has sufficient novelty and the reported results are solid. I have the following comments and suggestions for the authors.

1. The authors demonstrated laser operation at different energy transitions. So, I suggest to add a scheme of energy levels for Nd3+ ions.

R: We have incorporated Figure 1B into the manuscript, illustrating the energy transitions of the Nd:YLF crystal.

2. Please comment the system stability and power fluctuation for each operating mode.

R: After Table 2, we have provided a concise discussion regarding power fluctuation and its influence on the standard deviation of the measured values. The errors of the peak output power, shown in table 2, already incorporate the long term (different measurements during approximately 3 weeks) fluctuations.

3. There are typos, for example: line 189: 053 nm -> 1053 nm.

R: The typo was corrected, and the manuscript underwent a meticulous review.

Review 2

In the manuscript ' Efficient Trichromatic Nd:YLF Laser Emitting at 1047 nm, 1053 nm and 1314 nm ,' the authors Prado et al reported a Nd:YLF laser operating at 1047 nm, 1053 nm and 1314 nm using a diode-stack at 797 nm and a side-pumped structure. The high efficiency and power as well as the multi-wavelength operation have shown a great promise in applications. The manuscript can be accepted as the publication of Photonics after the following questions are answered.

1. The authors just described the focal length of the lens in the laser while no mentioning the designed mode size in the crystal. Therefore, the authors are encouraged to estimate the overlap efficiency and absorption efficiency of the laser.

R: We have supplemented the description with information about the focusing of the diode (measured spot size) and have compared it with the simulated mode size in the crystal. We used a MatLab script to calculate spectral overlap by convolution of the pump diode's emission curve with the Nd:YLF crystal's absorption spectrum. At a depth of 5.75 mm, absorption exceeds 97%. The effective absorption coefficient was used for calculating the overall overlap efficiency, as per Equation 1, resulting in an overlap efficiency of 98.3%.

2. The authors just mentioned their laser is promising in Q-switching operation while the current M2 is a little high to achieve this, as the mode size on the saturable absorbers should be smaller. How will the authors improve the system to achieve the Q-switching operation using saturable absorbers?

R: While the improvement of M² during Q-switching does occur (beam clean-up effect) and is important, in our experience with similar high-power pumped systems, very efficient Q-switched pulses can be generated with an M² much worse than the ones measured for this laser. For example, in our work [Prado, F.M.; Franco, T.J.; Wetter, N.U. Sub-Nanosecond, 41 MJ Pulse Energy, Passively Q-Switched Nd:YLF Laser. Opt. Laser Technol. 2023, 162, 109257, doi:10.1016/j.optlastec.2023.109257], we showcased a Q-switched Nd:YLF laser with an M²~6 that generated 41 mJ single pulse energy, with a peak power of 46 MW. One thing that is important to note is that the M² value of ~6 was generated after the beam clean-up effect, indicating a much higher M² during the QCW laser emission.

Other works also showcased Q-switched pulse generation with M2 close to 8 for Cr:YAG/Nd:YAG [Q. Yang, J. Ma, T. Lu, X. Ma, X. Zhu, 160mJ and 9ns electro-optics Q-switched conductively cooled 1047nm Nd:YLF laser, in: XX Int. Symp. High-Power Laser Syst. Appl. 2014, SPIE (2015), 64-73. DOI: https://doi.org/10.1117/12.2064316] and even an M2 of 9 for a Q-switched Nd:YAG laser with 53 mJ of pulse energy [K. Lee, H.C. Lee, J.Y. Cho, J.C. Lee, J. Yi, Passively Q-switched, high peak power Nd:YAG laser pumped by QCW diode laser, Opt. Laser Technol. 44 (7) (2012) 2053–2057, https://doi.org/10.1016/j.optlastec.2012.03.027].

3. In the introduction, another Nd-doped laser Nd:LuAG was not mentioned and the authors are encouraged to reference this laser like following:
4. Zhang, T. Liu, Y. Shen, C. Zhao, B. Huang, Z. Kang, G. Qin, Q. Liu, and X. Fu, “ 516 mW, nanosecond Nd:LuAG laser Q-switched by gold nanorods, ” Chin. Opt. Lett. 16, 030011 (2018).

R: We have included Nd:LuAG as one of the notable Nd-doped crystals, and have also referenced the paper indicated by the reviewer.