State-of-the-Art Technologies in Piezoelectric Deformable Mirror Design

Round 1

Reviewer 1 Report

In this paper, the authors present the production technologies to reduce the corrector size and to provide the stable performance of bimorph deformable mirror. The manuscript has some value for the researchers in the relevant area. The manuscript is well written and clearly presented. Some suggestions are as follows.

(1)  The authors said that chemical etching the insulating paths in the conductive layers deposited on the piezodisk is not quite applicable. However, some works have demonstrated that wet etching method combining with photolithography can pattern the electrodes in very small size. These works should be added and compared.

1. Zhu, Y. Li, J. Chen, J. Ma, and J. Chu, "Development of a unimorph deformable mirror with water cooling," Opt. Express 25(24), 29916-29926 (2017).

(2) It should be better to provide the figure about the electrode patterns with gap after laser ablation rather than a laser ablation setup.

(3) The authors said that presence of the astigmatism aberration is intrinsic for initial surface because of the fixing mechanism of the bimorph wavefront corrector in the housing. The fixing condition should be described clearly. From figure 2, we could not get this information.

(4) K – scaling coefficient depending on the boundary conditions. What is its value?

(5) um should be placed by μm through the whole manuscript.

Author Response

Thank you for the efforts and remarks. You can find our replies in the attached file.

Author Response File: Author Response.docx

Reviewer 2 Report

The team, headed by Prof.A.Kudryashov, is well known in the adaptive optics and laser communities. They have developed several good devices and first of all the so-called bimorph flexible mirrors. Such devices are now commercially available from this team and from corresponding industrial companies. One can either buy one of standard devices or order the custom-oriented mirror. During the last 25 or so years Prof.Kudryashov and his colleagues have published numerous journal and conference papers, devoted to development and design of such bimorph mirrors and to their application and implementation at various laser setups and facilities.

However, we are doubtful regarding the necessity to publish the manuscript under consideration. First, its title (“State-of-the-art technologies in piezoelectric deformable mirror design”) is absolutely misleading. Based on this title we have expected to see the review paper or at least the analytical analysis of the said devices. Note, that the piezoelectric components are used not only in the bimorph mirrors, but also in several other architectures – in unimorph ones, in mirrors with the stacked actuators etc. It is also important always to compare such kind of actuators with other types (magnetic, electric etc.). In fact, the manuscript simply describes one more variant of the same bimorph mirror without any comparison. The paper presents some interesting idea of how to improve the device performance, to optimize its size, to adjust the technology process etc. The paper adds a little if any novelty to the photonics, optics and laser science and technology. For the optical community its publication may be just a kind of advertising that our colleagues have reached some novel milestones in their efforts in developing new flexible mirrors. But such information does not correspond to the scientific agenda of the Photonics journal; it has to be published in commercial journals like Laser Focus World. Of course, there is some scientific and technical novelty in the manuscript, but it deals only with technology and processing issues; we can thus recommend to the authors to think about its publication in another journal – for instance, in the MDPI Micromachies, whose agenda is much closer to the content of this manuscript.

Author Response

We cannot agree with the reviewer that this paper is not suitable for this Journal - MDPI Photonics Journal is preparing a special issue on Adaptive Optics as we were informed. And thus, we considered the submission of our paper to it.

Reviewer 3 Report

This manuscript presents a method, based on laser ablation with appropriate welding technique, to produce small size piezoelectric deformable mirrors. This group of researchers is known worldwide for the production of medium size and large size bimorph deformable mirrors and the methods and techniques presented in the manuscript are representing an innovative steps compared to previous works. The manuscript is well presented with the appropriate level of details and results are convincing.

Only one minor point: the manuscript could have justified in one sentence the reason of the use of a 100 ns long laser pulse for the ablation in their case. Is it justified by the system cost and process or by the ablation physics ? Could shorter laser pulse giving the possibility to work with lower ablation threshold and less local thermal effects be an interesting alternative for further development of this mirror technology ?

I am recommending the publication of this work. 

 

Author Response

Thank you for high evaluation of our work and interesting question. The use of the laser pulse with the duration of 100 ns in our case was due to the cost of the whole system. The pulses with shorter duration could provide reduction of the thermal impact on the adjacent areas and lead to the reduction or even disappearance of the melt zone near the irradiated surface. You are right, in our case we faced a bit the problem of arising melting zones along of insulating paths boundaries. Such point could be considered as a further step in bimorph mirror construction investigation.

Reviewer 4 Report

The paper is devoted to the description of the innovative methods of producing the deformable mirrors in general (CVD, laser stereolithography, etc.) and the bimorph deformable mirror in particular (laser ablation and various microwelding methods). Obviously, the authors of the article are experts in the field of manufacturing the deformable mirrors and understand the main trends in this field of science. The used technologies of the mirror design were represented in particular detail. Main parameters of the bimorph deformable mirror were investigated such as local, the total stroke of the wavefront corrector, the first resonant frequency. The article also focuses on different unique features of the mirror manufacturing, which many researchers ignore: the quality of the initial surface, the ability to use the deformable mirror in the closed loop at the frequency close to its first resonance. I think this article is extremely appropriate for publishing in such optical journal as ‘Photonics’ and would be useful not only for specialists in adaptive optics area and also for the students and engineers.

However, a few moments in the paper are questionable and should be corrected:

1. How the tensile strength parameter was measured for this mirror? In addition, are such technologies applicable only to the bimorph deformable mirrors or can they be applied to some other wavefront correctors?
2. Was the electrode grid optimized?

After minor revision of the manuscript, this article for sure can be accepted for publication in the journal ‘Photonics’.

Author Response

We appreciate your efforts and your time spent for revision of our article. Here is our reply on your comments:

1. Testing of micro-welded joints was carried out according to the three-point scheme. The wire conductor was welded to two contact pads. The force was applied to the hook, which provided the tension. During the studies, the location of the breakage of the conductor and the force of separation were controlled. The microwelding technology was selected in such a way that the breakage was not in the contact area. The laser ablation technique in our opinion is uniquely applicable for the bimorph deformable mirrors. Talking about microwelding methods - they could be used also for high-resolution scalable piezostack cartridge-type deformable mirror where it is necessary to create the reliable connection between layers of piezoactuators with small spacing between individual actuators (<1 mm) (V.V. Toporovsky, A.V. Kudryashov, V.V. Samarkin, A.A. Panich, A.I. Sokallo and A.Yu. Malykhin, Journal of Physics: Conference Series, Volume 2103, International Conference PhysicA.SPb/2021 18-22 October 2021, Saint Petersburg, Russia).
2. The electrode grid of the mirror was adapted taking into account the necessity to provide the reliable compensation for at least of first 15 Zernike polynomials (in Wyant configuration), since their correction increases the spectral energy in the focus up to 90% for the beam propagating through the layer of Kolmogorov turbulence (Rukosuev, A.; Nikitin, A.; Belousov, V.; Sheldakova, J.; Toporovsky, V.; Kudryashov, A. Expansion of the Laser Beam Wavefront in Terms of Zernike Polynomials in the Problem of Turbulence Testing. Appl. Sci. 2021, 11, 12112.)