Preface: International Conference on Holography Meets Advanced Manufacturing (HMAM2) †

All the papers published in the volume are presented at the International Conference on “Holography Meets Advanced Manufacturing”, Online, 20–22 February 2023. Abstract: The CIPHR group, Institute of Physics, University of Tartu, Estonia, and Optical Sciences Center, Swinburne University of Technology, Australia, jointly organized the interdisciplinary online conference “Holography Meets Advanced Manufacturing” during 20–22 February 2023.


Introduction
To develop imaging concepts that go beyond the state-of-the-art, there has been significant collaboration in recent years between the research fields of holography and advanced manufacturing. This was the motivation for organizing the joint international conference between CIPHR group, Institute of Physics, University of Tartu and Optical Sciences Center, Swinburne University of Technology, a world leader in advanced manufacturing technology. The first day of the conference was dedicated to holography; the second day focused on advanced manufacturing; and the third day was devoted to industry applications.
This conference provided a platform for exchanging ideas, interdisciplinary, international collaboration, with three keynote talks from three world-renowned researchers, several invited talks from leading researchers across the globe, poster presentations of students, and industry-ready ideas for industry linkages. The submissions were accepted from the broad areas of holography and advanced manufacturing, which included digital holography, incoherent holography, computational imaging, microscopy, diffractive optics, quantitative phase imaging, structured light, tomography, optical security, cryptography, laser beam shaping, metalenses, micro/nanofabrication, femtosecond fabrication, OAM beams, optoelectronic materials and devices, non-diffracting beams, and space-time correlations and non-linear optics.
The keynote talks were scheduled for 35 min each and 10 min for a question session. The invited talks were scheduled for 15 min each, followed by 5 min for questions, while the poster presentations were allotted a duration of 10 min each, followed by 2 min for questions. Each day of the conference was divided into three sessions.
All the submissions were processed completely online using the Sciforum platform operated by MDPI. This includes the submission of abstracts, presentation files, and manuscripts, preliminary checks of format and template by event organizers, initial peer review of the submissions by event chairs, full peer review by external international reviewers, submissions of revised versions by the authors, and final checks and acceptance by the reviewers and event chairs. Further checks of compliance to MDPI standards including plagiarism checks were performed by the editors of Engineering Proceedings, published by MDPI. All accepted and presented submissions were published in Engineering Proceedings. Selected submissions were invited to the Special Issue on "Research in Computational Optics", organized by Prof. Vijayakumar Anand, Prof. Ravi Kumar, Dr. Andra Naresh Kumar Reddy, and Dr. Vinoth Balasubramani in the MDPI journal Photonics (IF-2.536), with APC waivers and special discounts https: //www.mdpi.com/journal/photonics/special_issues/B3GWFOP55V (accessed on 21 July 2023). In the Special Issue, three extended versions of the conference submissions have already been published.

Conference Organizing Committee
The following committees namely event organizers, event committee and event chairs for the three days are shown in Tables 1-3 respectively. were formed in October 2022 to effectively coordinate the three-day conference, and the event committee frequently met to review the procedures and steps needed to successfully carry out three-day conference.

Invitations and Participants
Approximately 30 leading researchers specializing in computational imaging from around the world received invitations to deliver an invited talk on the first day of the conference. We invited 25 leading researchers in advanced manufacturing to present an invited talk on day two of the conference. Approximately 50 industry members, mostly medical doctors and surgeons, were invited to give presentations on industry applications and their requirements. Several medical doctors and surgeons shared their difficulties in utilizing imaging and characterization tools, as well as features and capabilities they hope to see in the medical equipment and tools in the future. We sent out invitations to attend the conference and give poster presentations to more than 100 universities worldwide, more than 50 companies in Estonia and more than 100 companies globally.

Conference Programme
Day 1 of the conference was dedicated to Holography. Prof. Vijayakumar Anand started Day 1 of the conference by introducing the online conference on "Holography meets advanced manufacturing". Prof. Toomas Plank, Director of the Institute of Physics, University of Tartu, gave a warm welcome before the opening talk by Prof. Peeter Saari, Professor Emeritus, University of Tartu, on the topic of "Optics in Estonia: Research and Innovation Highlights". Prof. Joseph Rosen from the School of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Israel, delivered the keynote talk on "Advanced Imaging Methods Using Coded Aperture Digital Holography". Three sessions were held. Session 1 had six invited talks, presided over by Session Chair Prof. Vijayakumar Anand and Co-Chair Daniel Smith. Session 2 also featured six invited talks, and was presided over by Session Chair Dr. Vinoth Balasubramani and Co-Chair Andrei Bleahu. Prof. Vijayakumar Anand and Dr. Vinoth Balasubramani presided over Session 3 of the poster presentations. In the poster sessions, eight junior researchers presented their research. In all sessions, the presenters were introduced by the Co-Chairs.
Day 2 of the conference Prof. Vijayakumar Anand started Day 2 of the conference by giving a brief introduction to the program schedule. Prof. Saulius Juodkazis, Deputy Director of the Optical Sciences Center and Director of Nanotechnology, Swinburne University of Technology, Melbourne, Australia, presented the keynote talk on "Ultra-short laser pulses as material synthesis and lithography tool". Three sessions were held on the second day. Session 1 had five invited talks and was presided over by Session Chair Prof. Vijayakumar Anand and Co-Chair Daniel Smith. Session 2 featured four invited talks and was presided over by Chair Prof. Kaupo Kukli and Co-Chair Andrei Bleahu. Prof. Vijayakumar Anand and Prof. Kaupo Kukli presided over Session 3 of the poster presentations. In the poster sessions, six research scholars presented their work. In all sessions, the presenters were introduced by the Co-Chairs.
Day 3 of the conference Dr. Amudhavel Jayavel started Day 3 of the conference by introducing the program schedule. Prof. Heli Valtna presented the keynote talk on "Mapping the path from idea to economically scalable application in 3D imaging and sensing". Three sessions were held on the third day. Session 1 had four invited talks from medical doctors and was presided over by Chair Dr. Amudhavel Jayavel, and Co-Chair Andrei Bleahu. Session 2 featured four invited talks and was presided over by Chair Amudhavel Jayavel and Co-Chair Shivasubramanian Gopinath. Dr. Amudhavel Jayavel and Dr. Viktor Palm presided over Session 3 of the poster presentation. In the poster sessions, eight research scholars presented their work. All presentations are available on the YouTube channel CIPHR Talkies, and are permanently stored on the MDPI Sciforum platform.
The following shown in Table 4 is a complete conference schedule, including each speaker's name, the topic they presented, and their affiliations.

Proceedings and Certificates
The accepted and presented submissions of 27 articles were published in the MDPI (Multidisciplinary Digital Publishing Institute, Basel, Switzerland) journal Engineering Proceedings-Eng. Proc., 2023, HMAM2 https://www.mdpi.com/2673-4591/34/1 (accessed on 21 July 2023) . Selected submissions were invited to the Special Issue on "Research in Computational Optics" in the MDPI journal Photonics (IF-2.536).
Participation e-certificates were given to all the participants online via the Sciforum platform through the following link-Download the participation certificate from the Sciforum https://hmam2.sciforum.net/-Log In > My certificates. The e-Certificates were awarded to all the invited speakers, keynote speakers, poster presentations, and winner certificates for poster presentations.

Materials from the Conference
The materials from the conference are available in the following sections in the Sciforum online platform event, HMAM2-Holography Meets Advanced Manufacturing: Welcome message from the chairs, event calls, event organizers, event chairs, event speakers, sessions, conference schedule, instructions for authors, list of submitted submission, sponsors and partners, poster gallery. https://hmam2.sciforum.net/.

Conclusions
Our three-day online conference on "Holography Meets Advanced Manufacturing (HMAM)" organized by the CIPHR group, Institute of Physics, University of Tartu, Estonia, and the Optical Sciences Center, Swinburne University of Technology, Australia, was successful. The conference gave the CIPHR team opportunities to network with researchers and medical doctors across the globe.