Fiber-integrated terahertz spectrometer driven by ultrafast ytterbium doped fiber laser

Keskin, Hakan
In this thesis, development of a Terahertz time domain spectrometer (THz-TDS) driven by an ultrafast Ytterbium (Yb) doped ber laser, whose repetition rate can be tuned, was investigated to show that it can be used in Optical Sampling by Cavity Tuning (OSCAT) technique which enables the fast acquisition of THz pulse pro les. Central wavelength of the Yb-doped laser developed for this study is 1031 nm. The output average power was measured to be 90 mW which corresponds to about two nanojoule per pulse at 51 MHz repetition rate, and the pulse duration was measured with an autocorrelator to be 80 fs. Average output power and pulse duration stability of Yb-doped ber laser oscillator was examined at di erent repetition rates in order to test convenience of system for THz measurements. By tuning the repetition rate at 51 MHz by 25 kHz, we can scan a 100 ps time-window for the THz pulse measurement. This corresponded to a 6 mm cavity length tuning which altered the repetition rate of oscillator from by 53 kHz. Afterwards, THz-TDS system was built to understand the dependence of THz pulse pro le on the repetition rate of the Yb-doped ber laser. In this system InGaAs based photoconductive antenna (PCA) was used for THz generation and 2 mm thick <110> orientation ZnTe crystal was used in the detection part. Due to the limitation of the balanced photodetector with respect to the central wavelength of the laser, only a bandwidth up to 0.5 THz with a signal to noise ratio(S/N) of 60 was observed. THz signals measured at di erent cavity lengths overlap in both time domain and magnitudes which mean that THz measurements were not a ected by tuning the repetition rate of Yb-doped ber laser. In order to achieve this result, source parameters such as pulse duration and power of Yb-doped ber laser should be constant between measurements while scanning cavity length. By comparing THz signals at di erent repetition rates, it was shown that repetition rate tuning of Yb-doped oscillator can be used in OSCAT technique. In other words, we have shown that a Yb-doped ber laser can be used to rapidly scan the THz pulse pro le for future measurements.


Applications in broadband THz spectroscopy towards material studies
Türkşen, Zeynep; Altan, Hakan; Department of Physics (2011)
The purpose of this work was to construct and analyze a THz time domain spectroscopy (THz-TDS) system by using a nanojoule energy per pulse ultrafast laser (non-amplified ultrafast laser or oscillator) source and a non-linear optical generation method for THz generation. First a THz-TDS system, which uses photoconductive antenna (PCA) method for THz generation, was built to understand the working principles of these types of systems. This THz-TDS system which used PCA for generation and a 2mm thick <110> Zn...
Broadband THz Modulators Based on Multilayer Graphene on PVC
KAYA, Emine; Kakenov, Nurbek; Kocabas, Coskun; Altan, Hakan; Esentürk, Okan (2016-09-30)
In this study we present the direct terahertz timedomain spectroscopic measurement of CVD-grown multilayer graphene (MLG) on PVC substrate with an electrically tunable Fermi level. In a configuration consisting MLG and injected organic dopant, the transmitted intensity loss of terahertz radiation was observed with an applied voltage between 0 and 3.5 V.We showed that MLG on PVC devices provided approximately 100 % modulation between 0.2 and 1.5 THz at preferentially low operation voltage of ca. 3V. The obse...
End effect evaluation in rheological measurement of drilling fluids using Coutte coaxial cylinder viscometer
Gücüyener, I. Hakki; Kök, Mustafa Verşan; Batmaz, Taner (2002-05-01)
This paper demonstrates the order of influence of end effects on the application of a theory to determine and correct the end effects in Couette coaxial cylinder rotational viscometers, which are commonly used for the rheological evaluation of drilling fluids. It is found that higher shear stresses are measured due to end effects and, consequently, this error bearing shear stress-shear rate data leads to unreliable predictions of the rheological parameters. Evaluation of the shear stress-shear rate data obt...
Repetition Rate Tuning of an Ultrafast Ytterbium Doped Fiber Laser for Terahertz Time-Domain Spectroscopy
Keskin, Hakan; Altan, Hakan; Yavas, Seydi; İLDAY, Fatih Ömer; Yagci, M. Emre; Aydin, Ozan; Eken, Koray; Sahin, Behzat (2013-09-06)
Repetition rate tuning enables the fast acquisition of THz pulse profiles [1]. By using this method we demonstrate a compact and broadband terahertz time domain spectroscopy system (THz TDS) driven by ytterbium doped fiber laser source. The importance of this method is realized in that Yb: doped fiber lasers can be amplified to sub-millijoule pulse strengths more easily than other types of fiber lasers [2]. Hence, it has the potential to be used in excite-THz probe experiments. Furthermore, the repetition r...
Free vibration characteristics of a 3d mixed formulation beam element with force-based consistent mass matrix
Soydas, Ozan; Sarıtaş, Afşin (2017-09-01)
In this analytical study, free vibration analyses of a 3d mixed formulation beam element are performed by adopting force-based consistent mass matrix that incorporates shear and rotary inertia effects. The force-based approach takes into account the actual distribution of mass of an element in the derivation of the mass matrix. Moreover, the force-based approach enables accurate determination of free vibration frequencies of members with varying geometry and material distribution without any need for specif...
Citation Formats
H. Keskin, “Fiber-integrated terahertz spectrometer driven by ultrafast ytterbium doped fiber laser,” M.S. - Master of Science, Middle East Technical University, 2013.