Laser cooling of solids

Xuan Liu

Advisor: Prof.Heyuan Zhu and Deyuan Shen

 Department of Optical Science and Engineering,Fudan University

Abstract

Laser cooling of solids, also named anti-stokes cooling or fluorescence cooling , based on anti-stokes effect , in which process the cooling medium absorbs photons with longer wavelength and emits fluorescence photons with mean wavelength . The energy difference between these photons is compensated by absorbing phonons in the hosts and then the emission of fluorescence photons extract energy from the medium ,thus cause the temperature to fall.

In this report, I’ll first have a review on the reported work on laser cooling in the past decade. The idea of anti-stokes fluorescence cooling was first introduced by German physicist Peter Prinsheim in 1929^[1]. But because the lack of appropriate pump source, no net cooling was observed until 1995, researchers in Los Alamos National Laboratory demonstrated a temperature drop of 0.3K in Yb:ZBLANP glass^[2] . Great endeavor have been devoted to this field since then.  Those experiments have focused on absorption enhancement and cooling in new hosts with lower phonon energy. As the pump laser should be in the redtail of the absorption spectrum , the corresponding absorption is always very small, thus absorption enhancement has been necessary to fully utilize the pump power and to achieve higher energy conversion efficiency. Introducing additional reflection of pump laser back into the cooling medium , either by total internal reflection^[3] or by external high reflecting mirror^[3,4,5], is a widely used method to lengthen the absorption length. With this method , Seletskiy et.al reported a temperature as low as 155K in a Yb:YLF crystal^[6], reaching a cryogenic temperature lower than the 170K temperature barrier set by standard thermoelectric coolers. The refrigeration of a semiconductor load to 165K with this apparatus demonstrated that optical cooling has already been a viable alternative to traditional coolers^[7]. Another local cooling experiment showed that temperature as low as 110K could be achieved^[8]. Another novel method is called “Resonant Cavity Enhanced Absorption”^[9]. It exploited the destructive interference between different beams of reflected laser to greatly enhance the pump absorption. To fulfill the destructive interference condition, the length of the cavity is monitored and controlled in real time by a feedback system. Nearly 90% of pump laser was absorbed in this system.

Apart from all those novel method to enhance the absorption, great endeavors have been devoted to search for an appropriate medium which combines the advantage of higher purity and conversion efficiency. Hosts with lower phonon energy is a promising candidate because the non-radiative decay rates and the upconversion rates (in Er/Tm doped systems) are largely suppressed, thus the heat load introduced by these process is reduced to a rather low level.

In Er/Tm doped systems , the existence of upconversion and the following non-radiative decay have largely deteriorate the cooling performance. The reported cooling results in Er doped systems are limited to several kelvin in 800nm region^[10] or even tens of microkevin in 1550nm region^[11]. To further pin down the influence of upconversion in laser cooling process, we’ve built a numerical model to calculate the corresponding heat load introduced by upconversion and non-radiative process. The results shows that the non-radiative heat load plays the most important role. Hosts with lower phonon energy and non-radiative decay rates should be more promising in showing better results in these regions.

Reference:

[1]、Pringsheim P 1929 Zwei Bemerkungen ¨uber den unterschied von Lumineszenz und Temperature-strahlung Z. Phys.57 739–46

[2]、Epstein R I, Buchwald M I, Edwards B C, Gosnel lTRand Mungan C E 1995 Observation of laser-induced fluorescent cooling of a solid Nature 377 500–2

[3]、Hoyt C W 2003 Laser cooling in thulium-doped solids PhD Thesis University of New Mexico

[4]、Gosnell T R 1999 Laser cooling of a solid by 65 K starting from room temperature Opt. Lett. 24  1041–3

[5]、Edwards B C, Anderson J E, Epstein R I, Mills G L and Mord A J 1999 Demonstration of a solid-state optical cooler: an approach to cryogenic refrigeration J. Appl. Phys. 86  6489–93

[6]、Seletskiy D V, Melgaard S D, Bigotta S, Di Lieto A, Tonelli M and Sheik-Bahae M 2010 Laser cooling of solids to cryogenic temperatures Nature Photon.4 161–4

[7]、Seletskiy D V, Melgaard S D, Di Lieto A, Tonelli M, and Sheik-Bahae M 2010 Laser cooling of a semiconductor load to 165 K  Opt.Exp. 18 18061-66

[8]、Seletskiy D V , Melgaard S D, Epstein R I, Di Lieto A, Tonelli M, and Sheik-Bahae M 2011 Local laser cooling of Yb:YLF to 110 K. Opt.Exp 19 18229-36

[9]、Seletskiy D, Hasselbeck M P, Sheik-Bahae M, Epstein R I, Bigotta S and Tonelli M 2008 Cooling of Yb : YLF using cavity enhanced resonant absorption Proc. SPIE 6907 69070B

[10]、Fernandez J, Garcia-Adeva A J and Balda R 2006 Anti-Stokes laser cooling in bulk erbium-doped materials Phys. Rev. Lett.97 033001

[11]、Condon N J, Bowman S R, O’Connor P O, QuimbyRSand Mungan C E 2009 Optical cooling in Er³⁺: KPb²Cl⁵  Opt.Exp 17 5466–72

The Function of TAT Peptide-Conjugated Mesoporous Silica Nanoparticles for Drug Delivery

Tianlong Wang (王天珑）

Supervisor: Professor Peinan Wang

Department of Optical Science and Engineering, Fudan University

Abstract:

In contrast with the prior known organic drug carriers, novel inorganic materials-based systems have won more attention among researchers. Mesoporous silica nanoparticles (MSNs) have been focused on as ideal colloidal carriers for hydrophobic or hydrophilic drugs as well as genes to tumor tissues. They exhibit distinctive advantages including their large surface area, high pore volume, prominent biocompatibility, accessible surface functionalization and providing protection for the payloads. Nevertheless, conventional MSNs without surface functionalization are unintelligent materials due to the difficulty of drug release control. As expected to precisely control the drug–surface interaction, the superficial silanol groups resided on MSNs can be used to functionalize by organic silanes. For example, in the work presented here, we decorated with the carboxyl (–COOH) groups on the surface of MSNs. The hydrophilically modified MSNs with –COOH were beneficial for loading the water-soluble drugs through effective electrostatic attraction, such as doxorubicin hydrochloride (DOX). In addition, MSNs-COOH presented a distinct pH-responsible release behavior and a low cell toxicity to HeLa cells.

From the view of producing new materials for clinic use, we explored a method for the fabrication of core/shell architectural nanocomposites, wherein hydrophilic inorganic nanoparticles as core and MSNs as outer shell. The cationic surfactant of cetyltrimethylammonium bromide (CTAB) was adsorbed to various negatively charged inorganic nanoparticles including CdTe quantum dots (QDs). Then, QD@MSNs were prepared according to the sol–gel method. The performances for QD@MSNs, for instance, the cytotoxicity to normal cells, the uptake by cancer cells and the drug release behaviors, were also observed.

Furthermore, it has been shown that TAT peptide is an efficient molecule for transportation nanoparticles into cell nuclei via the binding import receptors importin α and β (karyopherin) and subsequently targeting the nuclear pore complexes (NPCs) of cancer cells and entering their nuclei.

As mentioned above, we have plunged ourselves into the intracellular nanodrug delivery systems based on TAT peptide-conjugated MSNs-COOH (MSNs-TAT). Take HeLa cells for example, we determine the optimal parameters such as pH, the proportion of TAT to QDs, The in vitro cellular evaluation towards KB cells was also unambiguously demonstrated.

References

[1] Baisong Chang, Xurui Zhang, Jia Guo, Yang Sun, Hongyan Tang, Qingguang Ren, Wuli Yang, Journal of Colloid and Interface Science.377, 644(2012).

[2] Limin Pan, Qianjun He, Jianan Liu, Yu Chen, Ming Ma, Linlin Zhang, and Jianlin Shi, J. Am. Chem. Soc.134,5722( 2012).

[3] Baisong Chang, Jia Guo, Congying Liu, Ji Qian and Wuli Yang, J. Mater. Chem.20,9947(2010).

[4] Baisong Chang, Xianyi Sha, Jia Guo, Yunfeng Jiao, Changchun Wang and Wuli Yang, J. Mater. Chem.21, 9239(2011).

[5] Qianjun He and Jianlin Shi, J. Mater. Chem.21, 5845(2011).

[6] Hongyan Tanga, Jia Guoa, Yang Sunb, Baisong Changa, Qingguang Renb, Wuli Yang, International Journal of Pharmaceutics.421, 388(2011).

[7] Corina Ciobanasu, Jan Peter Siebrasse, and Ulrich Kubitscheck, Biophysical Journal. 99, 153(2010).

[8] Zongxi Li, Jonathan C. Barnes, Aleksandr Bosoy, J. Fraser Stoddart and Jeffrey I. Zink, Chem. Soc. Rev.41, 2590(2012).

[9] Eun Seong Lee, Zhonggao Gao, Dongin Kim, Kyeongsoon Park, Ick Chan Kwon, You Han Bae, Journal of Controlled Release.129, 228(2008).

[10] Yi Wang, Wei Shi, Wenshuang Song, Li Wang, Xingang Liu, Jian Chen and Rongqin Huang, J. Mater. Chem.22, 14608(2012).

Optical Coherence Tomography

Ke Zhang

Supervisor: Jianhua Liu

Abstract:

Optical coherence tomography (OCT) has been developed for the imaging of biological microstructure with non-contact and non-invasion detection, high resolution, high sensitivity. The concept of OCT is first proposed in 1991 by Fujimoto group and they have obtained OCT images in the anterior segment, crystalline lens, and retina of human eyes in vitro. OCT have found widespread applications in medicine especially in ophthalmology. Standard OCT scheme based on a low time-coherence Michelson interferometer. Weak optical signal are reflected back from the inside of the multilayered tissue samples, and mix with the reference beam, Then we use high sensitivity of the lock-in amplifier to detect Interferometer dates and analysis dates to get what we want. Recently my work is to establish an OCT system, so I will share my basic dates of OCT system.

References

[1] D. Huang, E. A. Swanson, C. P. Lin, J. S. Schuman, W. G. Stinson, W. Chang, M. R. Hee, T. Flotte, K.Gregory, C. A. Puliafito, J. G. Fujimoto, Science ,254, 1178-1181 (1991).

[2] M. R. Hee, J. A. Izatt, J. M. Jacobson, and J. G. Fujimoto, Optics Letters,18, 950–952(1993).

[3] G.J.Tearney, B.E.Bouma, S.A.Boppart, et al., Optics Letters,21,1408-1410(1996).

[4] B.W.Colston, Jr., U.S.Sathyam, et al., Optics Express, 3,230-238(1998).

[5] Christoph K. Hitzenberger, Erich Götzinger, Markus Sticker, Michael Pircher and

Adolf F. Fercher, Optics Express,.9,780-790(2001).

[6]Tony H.Ko, D.C.Adler, J.G.Fujimoto, Optics Express, 12,2112-2119(2004).