A Solid-State Three-Stage Nd:YVO4 Laser Amplifier System Based on AOM Pulse Picker-Integrated Modulator
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe work under review studies a three-stage solid-state amplifier for laser pulses at the wavelength of 1064 nm. I can comment on it as follows:
- The term “hybrid” is used multiple times in the manuscript as referring to the system under investigation (in the title, in the main body, and in the Conclusion), but in fact, the studied system is predominantly solid-state. The seed generator is the only fibre component, and the type of seed generator is essentially unimportant; it could also be solid-state, and its emission parameters are not exceptional. The presented amplifier should be classified as solid-state. Section 3 begins with a sentence in which the presented three-stage amplifier is characterised as “hybrid”. But it is solid-state! This needs to be corrected.
- The pump powers (power 1, power 2, power 3) and the efficiency of the system (average output power as a function of total pump power = power 1 + power 2 + power 3) should be specified.
- It is necessary to indicate how the main obtained characteristics of the emission (pulse width of 8.09 ps and peak power of 3.7 MW) relate to other high-power systems (is this a lot or a little, or is the main feature the generation of a specified number of pulses?).
- More details regarding the resonant saturable absorber mirror should be provided. What is it made of, &c?
- In order for the results to be reproducible, the radii of curvature of lenses L1–L6 must be specified.
If the Authors take the above comments into account when revising the article, it may be published in “Quantum Beam Science”.
Comments on the Quality of English Languagen/a
Author Response
Comment.1: The term “hybrid” is used multiple times in the manuscript as referring to the system under investigation (in the title, in the main body, and in the Conclusion), but in fact, the studied system is predominantly solid-state. The seed generator is the only fibre component, and the type of seed generator is essentially unimportant; it could also be solid-state, and its emission parameters are not exceptional. The presented amplifier should be classified as solid-state. Section 3 begins with a sentence in which the presented three-stage amplifier is characterised as “hybrid”. But it is solid-state! This needs to be corrected.
Response: Thank you for pointing out the terminology issue. Upon re-evaluation, the system is indeed dominated by solid-state amplifiers, with only the seed source being a fiber component. The original description of "hybrid" was misleading and has been revised to "solid-state" throughout the manuscript (title, main text and conclusion).
Comment.2: The pump powers (power 1, power 2, power 3) and the efficiency of the system (average output power as a function of total pump power = power 1 + power 2 + power 3) should be specified.
Response: Thank you for your careful review and comments on the manuscript. Specific parameters for the pump power of each stage have been added to the experimental section (Section 3), such as the first-stage pump power range of 10–40 W, the second stage at 25-100 W and third stage at 20-90 W according to Fig.5, Fig.6 and Fig.7. The pump power will vary with the pump current.
Comment.3: It is necessary to indicate how the main obtained characteristics of the emission (pulse width of 8.09 ps and peak power of 3.7 MW) relate to other high-power systems (is this a lot or a little, or is the main feature the generation of a specified number of pulses?).
Response: Thank you for your careful work on this issue. This system achieves megawatt-level peak power while maintaining a single narrow pulse width (<10 ps), outperforming most pure fiber-based low-power systems (typically with peak power <1 MW). The adjustable pulse repetition rate (1 MHz) makes it suitable for applications such as laser ablation requiring high-energy pulses.
Comment.4: More details regarding the resonant saturable absorber mirror should be provided. What is it made of, &c?
Response: Thank you for your kind consideration on this issue. The resonant saturable absorber mirror (RSAM) uses a semiconductor saturable absorber mirror (SESAM) structure with a GaAs substrate and an InGaAs quantum well absorption layer. This part has been added in Section 3.
Comment.5: In order for the results to be reproducible, the radii of curvature of lenses L1–L6 must be specified.
Response: Thank you for such valuable question. L1 is convex lens and L2–L7 are all plano-convex lenses. Their focal length have been added to the experimental setup figure caption and the main text (Section 3).
Reviewer 2 Report
Comments and Suggestions for AuthorsPeer Review Feedback
- In your Abstract (Lines 9-10), you mention that fiber laser peak power is limited to the milliwatt level due to fiber characteristics. Could you be more specific about which characteristics cause this limitation? Also, how does your AOM pulse picker and hybrid amplifier setup specifically overcome these issues, beyond the general effect of reducing pulse frequency and subsequent amplification?
- The nonlinear Schrödinger equation is central to your discussion in Section 2.1 (Lines 70-71). How did you determine or estimate the group velocity dispersion (β2) and nonlinear coefficient (γ) for the fiber seed laser you used? It would be helpful to know if these values were based on direct measurements or simulations.
- You note in Section 3 (Line 110) that the pulse duration was measured as 8.09 ps, assuming a sech2 pulse shape, and Figure 2 also includes a Gaussian fit to the autocorrelation trace. Why was the sech2 shape assumed for the duration measurement, particularly when a Gaussian fit is also presented? It would also be interesting to understand how the calculated peak power (Line 14) might differ if a Gaussian pulse shape was used for the calculation.
- The dip in output power with 10 pulses in the third-stage amplifier (Section 4, Lines 173-174) is attributed to gain saturation. Could you delve a bit deeper into this? Specifically, why does increasing the pulse count from 8 to 10 trigger such a noticeable saturation effect in the final amplifier stage, apparently more so than in earlier stages or with fewer pulses?
- Your discussion on Amplified Spontaneous Emission (ASE) in Section 4 (Lines 209-210) concludes that it's mainly influenced by the first stage's pump power, and controlling this is key to mitigating ASE. Could you explain why the first stage has such a dominant role in ASE control compared to the later, higher-power stages? Are there particular design aspects or operating conditions of the first stage that make it especially critical for overall ASE levels?
Author Response
Comment.1: In your Abstract (Lines 9-10), you mention that fiber laser peak power is limited to the milliwatt level due to fiber characteristics. Could you be more specific about which characteristics cause this limitation? Also, how does your AOM pulse picker and hybrid amplifier setup specifically overcome these issues, beyond the general effect of reducing pulse frequency and subsequent amplification?
Response: Thank you for pointing out the issue. The abstract and introduction (Section 1) have been updated to explain that the limitations primarily stem from nonlinear effects in the fiber (such as self-phase modulation and stimulated Raman scattering) and the low optical damage threshold caused by the small core diameter of the fiber.
Comment.2: The nonlinear Schrödinger equation is central to your discussion in Section 2.1 (Lines 70-71). How did you determine or estimate the group velocity dispersion (β2) and nonlinear coefficient (γ) for the fiber seed laser you used? It would be helpful to know if these values were based on direct measurements or simulations.
Response: Thank you for your careful review and comments on the manuscript. β₂ (group velocity dispersion) is calculated using the formula , where is the angular frequency and is the wave number. γ (nonlinear coefficient) is calculated using the formula γ=2πn₂/(λAeff), where n₂=2.6×10⁻²⁰ m²/W (typical value for quartz fiber) and Aeff =50 μm² (mode field area of the seed fiber). These details have been added to the main text (Section 2.1).
Comment.3: You note in Section 3 (Line 110) that the pulse duration was measured as 8.09 ps, assuming a sech2 pulse shape, and Figure 2 also includes a Gaussian fit to the autocorrelation trace. Why was the sech2 shape assumed for the duration measurement, particularly when a Gaussian fit is also presented? It would also be interesting to understand how the calculated peak power (Line 14) might differ if a Gaussian pulse shape was used for the calculation.
Response: Thank you for your careful work on this issue. Mode-locked fiber lasers typically output sech²-shaped pulses, making this shape more accurate for pulse width calculation. The Gaussian fit in Figure 2 is a default software option used only for visualizing the pulse profile, with the actual pulse width based on the sech² fit result.
Comment.4: The dip in output power with 10 pulses in the third-stage amplifier (Section 4, Lines 173-174) is attributed to gain saturation. Could you delve a bit deeper into this? Specifically, why does increasing the pulse count from 8 to 10 trigger such a noticeable saturation effect in the final amplifier stage, apparently more so than in earlier stages or with fewer pulses?
Response: Thank you for your kind consideration on this issue. In the third-stage amplifier, the gain medium experiences energy injection exceeding the gain recovery time at high pulse numbers (e.g., 10 pulses), leading to depletion of the inverted population. The first two stages show less saturation due to lower pump powers. A kinetic analysis has been added to the discussion section (Section 4).
Comment.5: Your discussion on Amplified Spontaneous Emission (ASE) in Section 4 (Lines 209-210) concludes that it's mainly influenced by the first stage's pump power, and controlling this is key to mitigating ASE. Could you explain why the first stage has such a dominant role in ASE control compared to the later, higher-power stages? Are there particular design aspects or operating conditions of the first stage that make it especially critical for overall ASE levels?
Response: Thank you for such valuable question. As a pre-amplification stage, the first stage has a lower signal intensity at low pump powers, resulting in a higher proportion of spontaneous emission noise. Higher pump powers in the first stage significantly amplify ASE. In subsequent stages, the high signal intensity reduces the relative contribution of ASE.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe presented manuscript describing an advanced laser system combining fiber laser seed with AOM pulse picker module and three-stage amplification stage is an interesting design that will be worthy of the attention of the ultrafast laser community and of its potential users, e.g. for laser ablation. However, the manuscript needs to be improved before it is ready for publication, mainly in terms of formatting, English and corrections of not properly used terms.
Below are listed some of the instances that the authors should address in order to improve the paper.
A) Abstract, line 12 "the frequency of the reduced pulse train is amplified by a 12
hybrid three-stage Nd:YVO4 amplifier system"
How is the frequency of the reduced pulse train amplified by the amplifier system? Do tyhe authors have in mind that the intensity of the laser emission is amplified? Please specify.
B) Experimental setup, lines 144-153
in several occasions in this paragraph it is mentioned that M items are convex lenses,
for example "by convex lens M5", while in the experimental setup scheme Figure 1, all M items are designated as mirrors. Please correct this in the text.
C) line 150-151 "The structure of the third stage Nd:YVO4 amplifier is the same as that of the first stage."
In this sentence, is the comparison really to the first stage or to the second stage?
D) Validation results and discussion, line 155-157
"The purpose of this experiment is to make the amplified spontaneous emission (ASE)
of the output optical signal after passing through the three-stage amplifier as small as
possible, the output power as large as possible, the spot as round as possible, and the M2
as close to 1 as possible. "
This sentence can be improved in terms of academic style writing, e.g.
"The purpose of this experiment is to minimize the amplified spontaneous emission (ASE)
of the output optical signal after passing through the three-stage amplifier, ..."
E) line 161 "of seed laser" should be "of the seed laser"
F) line 162 "Set the crossover factor to 40 resulting in the pulse
frequency becoming 1 MHz."
should be e.g. "Setting the crossover factor to 40 results in the pulse
frequency becoming 1 MHz."
G) Figure 3 why are all the units in the figure a.u., even the time axis. If there is a reason for this, please discuss it in the text.
H) line 170 "output power increase with" should be "output power increases with"
Such a mistake is made several more times in the text, please resolve this.
I) line 178 "in Fifure 5." the dot is not needed here. Also, this is present a couple of more times in the text.
J) line 182-183 "variation curve of output power and ASE with pump
power changing is shown" should be changed to e.g. "variation curve of output power and ASE with pump power is shown"
K) line 199 "the efficiency will be inefficient." is not a good expression. Please rewrite it.
L) line 207 "the change curves" please change e.g. to "the variation curves"
M) in the references, please check references entries 6, 22 for missing space, references 10, 20 for missing information, and 8, 11, 19 for missing end page of the article.
Comments on the Quality of English Language
The English of the article can be improved. Some instances are already mentioned in the comments above.
Author Response
Comment.1: Abstract, line 12 "the frequency of the reduced pulse train is amplified by a hybrid three-stage Nd:YVO4 amplifier system" How is the frequency of the reduced pulse train amplified by the amplifier system? Do the authors have in mind that the intensity of the laser emission is amplified? Please specify.
Response: The abstract (Line 12) has been revised to "the intensity of the reduced pulse train is amplified by a three-stage Nd:YVO₄ amplifier system" to avoid terminological confusion.
Comment.2: Experimental setup, lines 144-153 in several occasions in this paragraph it is mentioned that M items are convex lenses, for example "by convex lens M5", while in the experimental setup scheme Figure 1, all M items are designated as mirrors. Please correct this in the text.
Response: Thank you for identifying this typo. M5 in Figure 1 is actually a mirror (HR 1064 nm). The main text has been corrected from "convex lens M5" to "mirror M5," and optical component labels are unified throughout the manuscript.
Comment.3: line 150-151 "The structure of the third stage Nd:YVO4 amplifier is the same as that of the first stage." In this sentence, is the comparison really to the first stage or to the second stage?
Response: Upon verification, the third stage has the same structure as the second stage (both use double-pass amplification with identical crystal dimensions and pump configurations). A revision has been added to the main text clarifying that to avoid ambiguity.
Comment.4: Validation results and discussion, line 155-157 "The purpose of this experiment is to make the amplified spontaneous emission (ASE) of the output optical signal after passing through the three-stage amplifier as small as possible, the output power as large as possible, the spot as round as possible, and the M2 as close to 1 as possible. " This sentence can be improved in terms of academic style writing, e.g. "The purpose of this experiment is to minimize the amplified spontaneous emission (ASE) of the output optical signal after passing through the three-stage amplifier, ..."
Response: Thanks for the reviewer’s kind suggestion. "The purpose of this experiment is to make..." has been revised to "The purpose of this experiment is to minimize...".
Comment.5: line 161 "of seed laser" should be "of the seed laser"
Response: Thanks for the reviewer’s advice. Typo errors throughout the text have been corrected.
Comment.6: line 162 "Set the crossover factor to 40 resulting in the pulse frequency becoming 1 MHz." should be e.g. "Setting the crossover factor to 40 results in the pulse frequency becoming 1 MHz."
Response: Thanks for the reviewer’s advice. Grammatical errors throughout the text have been corrected (e.g., "Set" to "Setting" in Line 162, "increase" to "increases" in Line 170).
Comment.7: Figure 3 why are all the units in the figure a.u., even the time axis. If there is a reason for this, please discuss it in the text.
Response: Thank you for your valuable question. Figure 3 shows relative time waveforms without calibrated actual time scales, so is the intensity axis, hence the use of arbitrary units (a.u.). The figure caption now includes a note: "The time and intensity axis are in relative scale."
Comment.8: line 170 "output power increase with" should be "output power increases with". Such a mistake is made several more times in the text, please resolve this.
Response: Thanks for the reviewer’s advice. Grammatical errors throughout the text have been corrected.
Comment.9: line 178 "in Figure 5." the dot is not needed here. Also, this is present a couple of more times in the text.
Response: Thanks for the reviewer’s advice. Typo errors throughout the text have been corrected.
Comment.10: line 182-183 "variation curve of output power and ASE with pump power changing is shown" should be changed to e.g. "variation curve of output power and ASE with pump power is shown"
Response: Thanks for the reviewer’s advice. Typo errors throughout the text have been corrected.
Comment.11: line 199 "the efficiency will be inefficient." is not a good expression. Please rewrite it.
Response: Thanks for pointing it out. We have revised the sentence.
Comment.12: line 207 "the change curves" please change e.g. to "the variation curves"
Response: Thanks for the reviewer’s advice. Typo errors the text have been corrected.
Comment.13: in the references, please check references entries 6, 22 for missing space, references 10, 20 for missing information, and 8, 11, 19 for missing end page of the article.
Response: Thanks for the reviewer’s kind advice. References have been systematically checked and corrected, with missing information added.
