الفهرس 
Femtosecond lasers in time and frequency domainsOnly 14 pages are availabe for public view
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Abstract
Precise distance measurement is of a great importance for several applications such as metrology and large-scale manufacturing. There are numerous optical techniques used to measure distances. Some of these techniques depend on frequency (wavelength) measurement, while others depend on time-of-flight. In frequency (or wavelength) dependent methods, such as multiwavelength interferometry and frequency scanning interferometry, optical frequency is considered as the reference for measured distance. In time dependent techniques, such as phase modulation, the distance is measured by accurately determining the time taken by the optical signal to a target.
The invention of a femtosecond optical frequency comb (OFC) opens a new era for optical length metrology. Its ultrashort pulses offer an accurate way for time detection and consequently a precise distance measurement tool. In frequency domain, the OFC has an extremely stable comb lines which are used as a frequency reference.
There are several techniques introduced to measure absolute distances using femtosecond lasers. One of the most common techniques is femtosecond pulses autocorrelation detection. There are two autocorrelation schemes used for distance measurement, collinear autocorrelation (interferometric) CAC and non-collinear autocorrelation (intensity). In this thesis, the non-collinear autocorrelation (NCAC) between femtosecond pulses is investigated as an alternative for the collinear autocorrelation for precise absolute distance measurement (ADM). In This study, the research compares between both techniques in terms of precision, accuracy, uncertainty and signal-to-noise ratio (SNR). In order to perform that, an autocorrelator is exploited to measure distances up to 21 meters using both techniques. Although both techniques showed similar precision, the NCAC technique enables longer distance measurement since it has higher SNR at higher gains without the coherence limitation of the CAC technique.
Electronic distance meters (EDMs) are widely used in different fields such as civil engineering and surveying. In this thesis and as an application for the investigated autocorrelation techniques, an indoor baseline is designed, constructed and accurately measured using femtosecond laser pulses to be used as a tool for EDM calibration. The baseline consists of 13 fixed bases that cover a total distance of 58 meters. In order to accurately measure the distances between the bases, autocorrelation between femtosecond pulses of the OFC is employed. The measurement shows an average standard deviation of 7 μm over the 58 meters distance. Although this deviation is dominated mainly by the inaccurate placement of the target mirror, it is fairly sufficient to calibrate the highest-accuracy EDM devices available in the market. The stability of the baseline is tested by measuring the inter-base distances over a period of one year.
Thesis chapters are presented as follows: Chapter 1 introduces briefly the main units especially the SI unit of length. It also explains the importance of using lasers in realizing this unit and in different length metrology applications.
Chapter 2 includes a description of femtosecond pulsed lasers in both time and frequency domains as well as mode-locking fundamentals. Laser mode-locking using both active and passive regimes as well as different schemes for mode-locking are discussed. Chapter 2 also includes a description of optical frequency comb and its main degrees of freedom.
Chapter 3 briefly describes some different techniques for distance measurement using femtosecond lasers. It also shows the use of optical femtosecond laser characteristics in measuring the absolute distance.
Chapter 4 includes the results of the experiments, where collinear and noncollinear autocorrelation schemes for femtosecond laser pulses used in distance measurement. The two schemes are described in detail. Distance up to 21 m is measured in a controlled environment using both techniques. A comparative study is made and uncertainty budget is calculated.
Chapter 5 describes a practical application for measuring distance using the femtosecond laser. A commercial electronic distance meter is calibrated using an indoor baseline. This baseline is constructed and well measured over one year to be used in performing the calibration process. All measurements and the uncertainty budget are included and discussed in this chapter.