High-Energy Injection-Seeded Single-Frequency Er:YAG Laser at 1645 nm Pumped by a 1532 nm Fiber Laser

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.       The author should present the novelty of this work in the introduction section.

2.       How the angle of 20^o was optimized? (sentence no. 20) In addition, I would prefer to add mirror abbreviations here for a quick figure analysis.

3.       In the caption of Fig. 1, include a full form of all abbreviations presented in Fig. 1.

4.       What is the coupling efficiency of the light in the coupled fiber?

5.       Why with increasing pump, the pulse duration is decreasing and pulse repetition rates are increasing?

6.       There are many minor mistakes in the paper. Please read the manuscript carefully and make corrections where required. Like, add space after Fig. 4 and Fig. 5 to start a new paragraph. Put space in the caption of Figure. 1.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Suggestions for revising the manuscript are as follows:

1.       In experiment, pulse energy decreasing was detected after injection seeding, could the author give more analysis about the reason of this phenomenon?

2.       Laser is frequency shifted by the acoustic-optic modulator (AOM), with an offset of 80 MHz. However，central frequency of the Fast Fourier Transform (FFT) spectrum of the heterodyne signal is 100 MHz, why is there a difference?

3.       In Fig.5, pulse width of beating signal seems greater than the pulse width of single-frequency laser, which is about 212 ns. Please explain this phenomenon.

4.       How about the M² factor in the y direction?

5.       In experiments, the optical-to-optical efficiency was quite low, some explains should be given.

6.       The pump laser is CW or pulsed? How much is the pump pulse width? The build-up time data in Fig.3 (b) were detected in experiments? Or simulated in theory?

Comments on the Quality of English Language

Moderate editing needed

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper "High energy injection-seeded single-frequency Er:YAG laser at 1645 nm pumped by a 1532-nm fiber laser" presents a master-slave Er:YAG Q-switched laser system, which can generate 5.5 mJ pulses at the repetition frequency of 200 Hz with 3.11 MHz linewidth and M^2 of 1.18. The results may be interesting for lidar applications.

Although the main results are well presented, the paper must be improved before it can be considered for publication. The following issues must be addressed:

 

1) The principle of operation and overall system design are very similar to several published works. For example, in [Li, S., Wang, Q., Song, R., Hou, F., Gao, M. and Gao, C., Laser diode pumped high-energy single-frequency Er: YAG laser with hundreds of nanoseconds pulse duration. Chinese Optics Letters, 18(3), p.031401 (2020)] and in [Shi, Y., Gao, C., Wang, S., Li, S., Song, R., Zhang, M., Gao, M. and Wang, Q., High-energy, single-frequency, Q-switched Er: YAG laser with a double-crystals-end-pumping architecture. Optics Express, 27(3), pp.2671-2680 (2019)] even better results in term of pulse energy and repetition rate were achieved with similar linewidth and the beam quality. What are the benefits of  the presented scheme?

2) More detailed description is needed for Figure 2. What blue and red curves represent in Fig.2 (a)? 

3) What element was used as a Q-switcher, how it was synchronized with the PZT driver? More information is needed about the "Ramp- Hold-Fire" technique used here to achieve Q-switched operation. 

4) How 40 kHz linewidth of NPRO was measured?

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript titled “High energy injection-seeded single-frequency Er:YAG laser at 1645 nm pumped by a 1532-nm fiber laser” reports a single-frequency, Q-switched Er:YAG laser. The authors used two 1532 nm fiber lasers as the pumping sources for the seed and slave laser, respectively. Employing a bow-tie ring resonator, a 1645 nm single-frequency seed-injection pulsed laser was realized with a pulse energy of 5.5 mJ, pulse width of 212 ns, a full-width half-maximum (FWHM) of 3.11 MHz, and an excellent beam quality factor of 1.18. The presented experimental results are noteworthy and interesting. Therefore, I think the paper is suitable for publication after the following minor revisions.

 1.      In the introduction, the authors should summarize the papers on single-frequency Er:YAG laser in the form of a table, and explain the innovative points of this paper. The table should include details such as, the pumping source (fiber laser or laser diode), laser wavelength, and the output parameters (energy, pulse width, linewidth, etc).

2.      Besides the seed-injection mentioned in this paper, are there any other methods that can also achieve a single-frequency pulsed laser? The authors should discuss these methods in detail in the introduction.

3.      The authors should provide detailed parameters of the 1532 nm fiber laser used in the seed and slave laser, such as the core diameter, NA, etc.

4.      In Fig. 2 (b), the unit of intensity is given as a.u. The authors may want to use arb. unit. I suggest the authors normalize the intensity, as shown in Fig. 5.

5.      What does it mean that the single-frequency laser operates at the central frequency of about 100 MHz, as mentioned in line 172 on page 5?

6.      In Fig. 6, the beam quality of the single-frequency pulsed Er:YAG laser is displayed, however, the beam quality in the vertical (y) direction has not been measured.

Comments on the Quality of English Language

The overall English is good, some minor modifications of English language can be made.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have incorporated all the comments and I suggest manuscript to be published in current form.

Author Response

Thanks for your works on our manuscript. please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

 

The paper improved somewhat but many issues still present.

 

Query 1:

....."However, the stability of the single-frequency laser energy is only measured in 30 minutes, with a root mean square (RMS) less than 1.5 MHz, which is lower than this manuscript."....

In the current paper the frequency stability was not measured at all, so the statement is incorrect.

And nothing from the response was added to the main text, except two references.  

 

 

Query 2:

“In Fig. 2 (a), the laser operates in single-longitudinal-mode (blue line represents the sawtooth-wave signal, red line represents the laser signal).”

This is not a valid description. What is being varied and what is being measured? Also, the image quality is very poor.

 

Query 3:

The description of "Ramp-Hold-Fire" technique was given in the response letter, but not in the text. And no references added. So the manuscript itself was not improved.

 

Query 4:

“Besides, the linewidth of the NPRO seed laser is approximately 40 KHz, measuring with the method of the delayed self-heterodyne laser linewidth measurement [20].”

 This is the only appropriate modification made regarding my comments.

 

 

Author Response

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Round 3

Reviewer 3 Report

Comments and Suggestions for Authors

Now the paper can be accepted.