A Hybrid Self-Seeded Ti:sapphire Laser with a Pumping Scheme Based on Spectral Beam Combination of Continuous Wave Diode and Pulsed DPSS Lasers

Round 1

Reviewer 1 Report

Authors developed CW Tisapphire oscillator and pulsed amplifier combined so the efficient 2nd harmonic generation is possible. Authors need to show some more measured results. Figures and Tables are too clear to be seen. It is very hard to find some errors in entire manuscript.English grammars are also fine.Therefore, the manuscript is suitable for the publication for this time. There are some minor comments.

1. Please use abbreviated journal names in the reference section.
2. In Figure 9, what are the highest detuning frequency for CW and CW+pulsed mode ?
3. Figures 2-5 labels are small to be seen.
4. Figure 1 fonts need to increased.
5. Please provide company information in Line 106 and 110.
6. What about the stability of the developed method ?
7. How about FWHM verse power ?

 

 

 

Author Response

I thank the reviewer for his positive response to our manuscript. Regarding his points of criticism I made the following adaptations:

1. Please use abbreviated journal names in the reference section.

Full journal names have been replaced by the recommended abbreviation

2. In Figure 9, what are the highest detuning frequency for CW and CW+pulsed mode ?

The maximum tuning ranges observed during the measurement displayed in Figure 9 were 11.67 GHz for CW+pulsed mode and 11.58GHz for the CW-mode. In the text description, the mention of the tuning range of 12 GHz was changed to "nearly 12GHz". As discussed in the article, this is not a fundamental limit, but rather depends on the choice of etalon FSR, piezo actuator range, and other parameters.

3. Figures 2-5 labels are small to be seen.

Label font sizes on y-axis has been increased by up to 50% and abbreviations were introduced to avoid a too large overall size. The fonts are still a bit smaller than the manuscript text size, but figures will be uploaded in sufficient quality to allow zooming in further if needed.

4. Figure 1 fonts need to increased.

The font size was increased by about 25% for each labeled item.

5. Please provide company information in Line 106 and 110.

Company information was added for the blue diodes (Nichia) and the Nd: YAG pump laser (Edgewave GmbH). The diodes are effectively some kind of grey-market items, as they are extracted from commercial laser projector systems and resold by second-party resellers and are not available directly from the manufacturer Nichia, or only in large quantities to other OEM companies.

6. What about the stability of the developed method?

I am not quite sure which "stability" measures are referred to here, if the long-term operation is meant, then the systems can be run over several days without interruptions in locked mode, though the lab temperature needs to be fairly stable to keep the temperature drifts of the cavity length within the range that can be compensated by the piezo-actuator. Long-term drifts over several hours of the wavelength have not yet been evaluated. However, the focus of the paper was more on the method and its first demonstration, so stability concerns were not a priority. We believe the method does not introduce significant stability issues compared to the classic oscillator cavity + amplifier cavity approach, rather we consider that it may be more stable, as the mode-matching between 'seed' and 'amplifier cavity' is effectively always perfect in our approach, as the same cavity is used.

7. How about FWHM verse power ?

The dependence of pump energy on FWHM line-width has not been measured in our system yet and would of course be an interesting follow-up investigation. It can generally be expected that higher pulse energies result in shorter pulse duration and thus a wider Fourier-transform limited line-width. Additionally, higher energies will result in stronger chirp effects during the pulse due to short-term changes in the crystal's refractive index due to the pump pulse intensity. Nevertheless, these same factors are also present in the other alternatives mentioned in the literature references.

 

Reviewer 2 Report

Dear authors,

Even I'm not completely convinced about the advantages of having the narrow band seed and the pulsed amplification in the same cavity and additionally in the same laser crystal, I think that your paper is worth to be published as ist is. The approach of using completely different commercially available pump sources is noteworthy. Measures to circumvent disadvantages were proposed by yourself and I am curious to read about these improvements in future. Thank you for sharing this nice work with the community.   

Author Response

We thank the reviewer for his opinion on our prototype system. We agree with the reviewer that in the present condition the advantages of the system are not so pronounced if considering the limitations such as lower power and efficiency compared to the two-cavity setups.

However, as also mentioned by the reviewer, our proposed improvements may significantly alleviate these issues, making the system more suitable for additional applications.

As the reviewer did not point out specific points of criticism, we only performed an additional check of the English language as they recommended a minor spell check, both by using some electronic grammar assistant as well as support by other colleagues.

Reviewer 3 Report

The authors present a wavelength stabilized ti-sapphire laser where a CW mode pumped by blue laser diodes allows the cavity to be locked to a single frequency via an air-spaced etalon. The air-spaced etalon is controlled via feedback to ensure stable cw operation and tracks the ring cavity longitudinal mode. The novelty here is that the laser lock is maintained while operating cw with blue pump diodes, and this single mode stability is maintained when a high pulse energy pump laser is applied to generate a pulsed output on top of the low power cw emission.

Overall this is nicely presented work, and would certainly be of interest to the laser community.

Specific technical comments:

• The laser is observed/ measured to operate without mode-hops, however could the authors estimate/ measure how much the frequency is ‘dithering’ over time ? While it is ‘single mode’ this does not estimate the lasers frequency excursions over time.
• The authors discuss the fact that the doubled Nd: YAG pump laser has an excellent beam quality, and state that the Rayleigh range of this pump is shorter than the crystal length. In contrast the blue pump diodes are multi-mode and will have a significantly larger spot size/ shorter confocal region. Could this be estimated, and an estimate made of the overlap of the blue laser diodes with the cavity mode ? Is the beam quality of the CW and pulses laser identical? which would support the same transverse mode is operating.
• The pulsed pump is ~ 1ns, however the laser pulse is ~ 73 ns. Why is this substantially longer ? Is this related to the cavity lifetime ? I assume the cavity lifetime is the cause here, however I recall the lifetime of Ti-sapphire is only several ns – so would this mean that the pulse amplification is only occurring for a few ns, and then the rest of the pulse length is not being amplified ? Could a shorter cavity lifetime provide a higher laser efficiency ?
• It is a shame the pulse was not measured with a high bandwidth detector + oscilloscope (> 1 GHz) to better see the temporal dynamics – is this possible ?

Grammar:

Line 261: Please correct ‘were one’.

Author Response

Please see the attachment

Author Response File: Author Response.pdf