Volume 7 • Issue 1 • 1000196 J Biosens Bioelectron ISSN: 2155-6210 JBSBE, an open access journal Research Article Open Access Journal of Biosensors & Bioelectronics J o u r n a l o f B i o s e n s o r s & B i o e l e c t r o n i c s ISSN: 2155-6210 Rahman et al., J Biosens Bioelectron 2016, 7:1 http://dx.doi.org/10.4172/2155-6210.1000196 *Corresponding author: Anis Rahman, Applied Research and Photonics, 470 Friendship Road, Suite 10, Harrisburg, PA 1711, United States, Tel: 1717-220- 1003; E-mail: a.rahman@arphotonics.net Received November 02, 2015; Accepted January 08, 2016; Published January 18, 2016 Citation: Rahman A, Rahman AK, Tomalia DA (2016) Dendrimer Dipole Excitation: A New Mechanism for Terahertz Generation. J Biosens Bioelectron 7: 196. doi:10.4172/2155-6210.1000196 Copyright: © 2016 Rahman A, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Keywords: Electro-optic Dendrimer; Dipole Excitation; Terahertz Generation Introduction Currently, the so-called diference frequency generation (DFG) process [1] eliminates the use of a femto-second pulsed laser method for pulsed terahertz generation such as photo-conduction [2] and optical rectifcation [3]. Herein we now introduce a new and diferent mechanism; namely, dendrimer dipole excitation (DDE), as a strategy for tunable, continuous wave (CW) terahertz generation. Dendrimers are core-shell macromolecules possessing spherical molecular structure. Te molecular size of a dendrimer is controlled by the number of concentric shells around the core; wherein, each shell is known as a generation (G) [4]. Figure 1 shows the molecular structure of a dendrimer having three shells around the central core (G3). Each terminal group is capable of attaching two monovalent dopant molecules; thus the total number of probable dopants per dendrimer molecule is given by 2 (G+2) . When the dendrimer is doped with a suitable chromophore, multiple dipole moments are created because of the distribution of charge centers within the dendrimer molecule. As can be reasonably assumed from the molecular structure of a dendrimer, these dipoles have a distribution of dipole moment, because of the spacing distribution of the charge centers. As such, the equation for dipole moment, is µ=ql rewritten as, µ(x)=ql(x) where μ is the dipole moment, q is the charge, and l is the separation between the negative and positive charges forming the dipole. Figures 2a and 2b shows the energy level diagram of diference frequency generation [5] and Figure 3 shows the schematic of possible energy levels in an electro-optic (EO) dendrimer resulting from chromophore induced dipole moment distribution created by the doping process. If this dipole distribution is excited by a suitable pump laser, a broadband emission is expected which falls in the terahertz range. Dendrimer Dipole Excitation: A New Mechanism for Terahertz Generation Anis Rahman 1 *, Aunik K. Rahman 1 and Donald A Tomalia 2 1 Applied Research and Photonics, 470 Friendship Road, Suite 10, Harrisburg, PA 17111, USA 2 Nano Synthons LLC, 1200 N, Fancher Avenue, Mt. Pleasant, MI 48858, USA Abstract An electro-optic dendrimer (EO dendrimer) material has been designed for high power terahertz generation. An ordinary poly (amidoamine organosilicon) (PAMAMOS) dendrimer was modifed via doping and poling to generate a high electro-optic coeffcient nanomaterial. Measured EO coeffcient varied from ~130 pm/V at 633 nm to ~90 pm/V at 1553 nm. An emitter designed from this EO dendrimer generates milliwatts of continuous wave (CW) terahertz radiation (T-ray) when pumped by a CW laser of suitable wavelength. The mechanism termed as the dendrimer dipole excitation (DDE) works via excitation of the dipole population generated by the doping process. The doping protocol also generates a distribution of dipole moments, as opposed to fxed dipoles in the lattice of a crystalline material; thus, when excited by a suitable pump laser, these dipoles radiate a broadband frequency that range from 0.1 THz to ~ 30 THz. A terahertz time-domain spectrometer (TeraSpectra) was designed with this DDE terahertz source. As a test of the spectrometer functionality, a standard polyethylene calibration was conducted. It was found that TeraSpectra reproduces several known absorbance peaks of polyethylene. It also produces additional absorbance peaks not observed before. It is surmised that the ultra-high sensitivity of T-ray enables observation and discovery of additional absorbance peaks that are not visible via other spectroscopy such as visible, UV, FTIR or Raman. Figure 1: Molecular structure of a dendrimer. The terminal groups each have two sites available where dopant molecules may be attached. Thus a distribution of dipoles per molecule is possible via chromophore doping. (a) (b) Figure 2: (a) Interaction geometry for difference frequency generation and (b) Energy-level diagram of difference frequency generation [4].