High power Tm:YAG slab laser

Name: Xuan Liu

Supervisors: Heyuan Zhu, Deyuan Shen

     After the rapid development in the past decades, various kinds of laser, including gas-state laser, solid-state laser and liquid-state laser, etc , have gained wide applications in many fields. As to the solid-state laser, especially those lasers working with traditional crystals, the power level has already surpassed tens of kilowatts and is now nearly reaching hundreds of kilowatts^[1]. The deterioration of laser performance caused by kinds of thermal effects have been a big obstacle for further enhancement of the power level. Every small development results from some technical improvements in suppressing the thermal effects. Traditional crystals with rod-like shape suffers from severe thermal effects such as thermal-lens effect, thermal stress effect, thermal shock and the highest power that could be obtained with them is largely limited^[2]. Special shapes with larger aspect ratios are proposed to dissipate the heat introduced in laser processes more efficiently. Slab lasers and thin disk lasers are among them. Larger aspect ratios has ensure the quasi-one dimensional temperature distribution in slabs and disks. By properly arranging the propagation direction of the laser beam, thermal effects could be compensated .

Lasers in 2um region experienced high absorption in water , making them very suitable for medical applications^[3]. The eye-safe nature^[4] of laser in this region has ensured wide use in laser processing and military technologies. Besides, the emission wavelength of Tm lasers can be tuned over a wide spectral interval, from approximately 1.8 to over 2 um, encompassing a large number of transitions of molecular species, which turn out to be particularly important for environmental applications. In this respect, Tm-based lidar systems may represent a valuable alternative to Nd-based systems for monitoring ozone and most greenhouse gases, such as water vapor, carbon dioxide, methane, and nitrous oxide, owing to the presence of strong absorption lines of these species at around 1.9 um^[5].

The use of polycrystalline ceramics as a new type of laser gain host has been intensively investigated in recent years because they have several advantages over single-crystal hosts.^[6] For example, ceramic samples with a high doping concentration and a large size can be easily fabricated, whereas this is extremely difficult for single crystals: multiplayer and multifunctional ceramic laser materials are possible because of the polycrystalline nature of ceramics. Potentially, because of the short period of fabrication process and because they can be mass produced, the cost of ceramic laser materials could be much lower than that of single crystals. In particular, no complicated facilities and critical techniques are required for growth of ceramics. And the similar laser performance of optical ceramics compared to single crystals have proved that ceramics could be a good alternative for single crystals. And the possibility to fabricate ceramics with larger sizes made the use of ceramics in slab lasers very promising.

In this report, we’ll have a brief introduction of the development history of slab lasers. Several kinds of design will be discussed .

References:

[1]、新一代百千瓦高平均功率板条激光器研究进展，激光与光电子学进展2009,01

[2]、The Slab Geometry Laser-Part  I:  Theory，IEEE  JOURNAL  OF QUANTUM  ELECTRONICS,  VOL.  QE-20, NO.  3, MARCH  1984

289

[3]、Cw high power IR-laser at 2µm for minimally invasive surgery, D. Theisen, V. Ott, H.W. Bernd, V. Danicke, R. Keller, R. Brinkmann, Therapeutic Laser Applications and Laser-Tissue Interactions, Rudolf W. Steiner, Editor, Proceedings of SPIE-OSA Biomedical Optics, SPIE Vol. 5142 (2003)·

[4]、Diode-Pumped Lasers  at Five  Eye-Safe Wavelengths,    Tracy  S. Kubo and Thomas  J. Kane,  Member, IEEE  JOURNAL OF  QUANTUM ELECTRONICS,  VOL.  28.  NO. 4, 1033,  APRIL 1992

[5]、 High-efficiency diode-pumpedTm: GdLiF₄ laser at 1.9 um

Nicola Coluccelli, Gianluca Galzerano,Francesco Cornacchia,Alberto Di Lieto,Mauro Tonelli,and Paolo Laporta.  November 15, 2009 / Vol. 34, No. 22 ,P 3559/ OPTICS LETTERS

[6]、Diode-end-pumped 4.2-W continuous-wave Yb: Y ₂O₃ ceramic laser。

J. Kong and D. Y. Tang，OPTICS LETTERS / Vol. 29, No. 11 / June 1, 2004

Manipultion of metal cluster on Pt(111)surface with single-atom tip

Dong Guofeng

Tutor:Zhuang Jun

The structural and the dynamical behaviour of clusters of atoms deposited over a substrate are technologically very important.For instance, they determine the growth mode in various vacuum deposition techniques, as well as the physical and chemical properties of the resulting interface.On the one hand, such techniques promise the possibility of construction of novel materials with tailormade properties. For these reasons, there have been extensive experimental studies of the properties of clusters on various surfaces, especially using atomic imaging techniques such as field ion microscopy (FIM), and scanning tunneling microscopy (STM) .

About supported cluster on Pt(111) surface, we study the influence of STM tip on medium sized cluster.In the case of Pt homogeneous system, the tip can affect the positon of the cluster on the surface.For the different activation energy, the Pt cluster is supposed to be in the fcc site.However, if the single-atom tip apex is put in the hcp site,the equilibrium postion of the cluster will be in the hcp site.We also study the different result of tip in different height. By this way, we construct a nucleus in the hcp site, which maybe eventually form a nanosturctuer in the hcp site.

References:

1.Vassilios Papathanakos,G.A.Evangelakis,Structural and diffusive properties of small 2D Au clusters on the Cu(111) surface,2002,Surface Science,499 229

2.Pablo Jensen,Growth of nanostructures by cluster deposition: Experiments and simple models,1999,Revies of Modern Physics,71 1695

3.Peng Zhang, Yiqun Xie et al, Equilibrium structures and shapes of clusters on metal fcc(111) surfaces, 2008 Nanotechnology, 19 255704.

4.Jianxing Jiang, Peng Zhang et al, Diffusions of small clusters on Pt(111) and Cu(111) surfaces, 2008 Applied Surface Science, 254 5822.

5.Maria Flytzani-stephanopoulos et al,Atomically Dispersed Supported Metal Catalysts,2012,545

Simulation of atom manipulation via thermal activation on metal fcc(001) surfaces

Chang Chen

Supervisor: Jun Zhuang

Single atom manipulation has attracted great attentions because of its intriguing applications in nanofabrication and surface      modification at an atomic level. After the pioneering work by Eigler et al many subsequent researches have been carried out on both experimental and theoretical sides，of which a substantial portion is dedicated to the lateral manipulation at cryogenic temperatures. On most other surfaces or systems, however, when the interactions between the manipulated atom and substrate is strong, the lateral manipulation usually needs other assistances besides the tip as in these cases existence of the tip could only lower but not eliminate the energy barrier. With the assistance of thermal activation, it is therefore unnecessary to eliminate the diffusion barrier along the manipulation direction, which makes the lateral manipulation be possible on the strong atom-substrate interaction surfaces. We study a thermal activated method for lateral manipulation of single atoms on Ag(001) and Pt(001) surfaces using both molecular statics (MS) and molecular dynamics (MD) methods. Our simulation results show that at high temperatures adatoms can diffuse under the tip via spontaneous hopping or exchange mechanism. When we place the tip at certain proper heights, these desired movements along target path can take a nearly one-hundred-percent portion of all the diffusions, suggesting a novel way to controlling atoms with fascinating reliability. We also find existence of the tip has greatly decreased the activation energy of some diffusion ways while restrict other ones so that the adatoms move towards the tip more likely and frequently, which is the essence of this successful lateral manipulation via thermal activation. Changes of diffusion directions and mechanisms with statistical method at different tip heights are also investigated.

Reference

[1] Eigler D M and Schweizer E K Nature 344 524(1990)

[2] Crommie M F ,Lutz C P and Eigler D M Science 262 218(1993)

[3] Yiqun Xie  Nanotechnology 19 335710(2008)

[4] Yiqun Xie  APL 95 073105 (2009)

[5] Jun Zhuang and Lei Liu PRB 59 13278(1999)

[6] Michael I. Haftel and Mervine Rosen PRB 64 195405(2001)

[7] Jianxing Jiang  Applied Surface Science 254 5822 (2008)

[8] J. R. Sanchez and J. W. Evans PRB 59 3224 (1999)