Hermann Harde

Helmut Schmidt University, Electrical Engineering, Faculty Member

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Biography
1966-1970 studies with focus on atomic and laser physics at the Technical University Hannover.
1971-1974 scientific assistant and PhD at University of Kaiserslautern.
1975 Professor for Laser-Engineering
1982 Professor for Laser-Engineering and Materials Science at the Helmut-Schmidt-University Hamburg.
1990 and 1992 Visiting Scientist at IBM Watson-Research Center, Yorktown Heights, New York
1995 and 1996 Visiting Scientist at Oklahoma State University, Stillwater, Oklahoma
1995 - 1997 Dean of School of Electrical Engineering, Helmut-Schmidt-University, Hamburg
1997 - 1999 Vice-President of Helmut-Schmidt-University, Hamburg
2010 retired

Research fields:
- generation and detection of ultrashort light pulses
- propagation of ultrashort light pulses in optical fibers
- quantum interference effects in atoms and molecules
- gas sensors for medical and environmental applications
- cleaning and micro-structuring with lasers
- far IR-spectroscopy with femtosecond terahertz pulses
- propagation of electromagnetic radiation in the atmosphere
- influence of greenhouse gases on climate

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Papers by Hermann Harde

The Detection and Attribution of Northern Hemisphere Land Surface Warming (1850–2018) in Terms of Human and Natural Factors: Challenges of Inadequate Data

Climate, Aug 27, 2023

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Pulse Evolution in Birefringent Fibers under the Influence of Four-Wave Mixing and Stimulated Raman Scattering

Nonlinear Optics: Materials, Fundamentals, and Applications

The propagation of high power laser pulses through glass fibers is affected by nonlinear optical ... more The propagation of high power laser pulses through glass fibers is affected by nonlinear optical effects which can be described by the third order nonlinear susceptibility χ(3) = χ′(3)+ iχ″(3). The real part contains self- and cross-phase-modulation (SPM and XPM) causing spectral broadening, and it is responsible for the parametric four wave-mixing process (FWM) which leads to the generation of a Stokes/anti-Stokes wave pair and requires phase matching. The imaginary part describes Stokes frequency conversion due to stimulated Raman Scattering (SRS). This process is always self phase matched. Most of the research work published has treated the effects of SRS and FWM independently [1] even though they may act simultaneously [2]. A simultaneous treatment becomes necessary when the frequency shift at which phase matching occurs falls within the Raman amplification profile. In this paper we present experimental and theoretical results of the combined action of FWM and SRS in a birefring...

<title>Nonlinear Propagation Effects In Birefringent Fibers</title>

Nonlinear Optical Materials, 1989

ABSTRACT Nonlinear propagation effects in birefringent optical fibers are investigated and their ... more ABSTRACT Nonlinear propagation effects in birefringent optical fibers are investigated and their implications for generating ultrashort light pulses in the IR are discussed. Stable compression of intense Nd:YAG laser pulses is obtained due to combined action of self-phase modulation, stimulated Raman scattering, and group-velocity dispersion. First operation of a fiber-grating Raman laser with subpicosecond output is demonstrated in the regime of positive group-velocity dispersion.

Time-domain spectroscopy of molecular vapors with subpicosecond pulses of THz radiation

Measurement of First-Order Free-Induction-Decay in Cs

Methods of Laser Spectroscopy, 1986

We present a new approach for observation of first-order free-induction-decay (FID), which can se... more We present a new approach for observation of first-order free-induction-decay (FID), which can sensitively be detected by means of polarization selective devices. FID in Cs vapor is measured with picosecond time resolution, and for the first time beats due to the hyperfine splitting of the ground and first excited state with 9.2 GHz and 1.2 GHz can be observed on the fast decay curve.

EDP Sciences, Les Ulis DOI: 10.1051/jp4:2005125178 Isotope-selective sensor for medical diagnostics based

Abstract. Development of new optical sensor technologies has a major impact on the progression of... more Abstract. Development of new optical sensor technologies has a major impact on the progression of diagnostic methods. Of the permanently increasing number of non-invasive 13C-breath tests, the Urea Breath Test for detection of Helicobacter pylori is the most prominent. However, many recent developments go beyond gastroenterological applications. We present a new detection scheme for breath analysis that employs an especially compact and simple set-up based on Photoacoustic Spectroscopy. Using a wavelength-modulated DFB-diode laser and taking advantage of acoustical resonances of the sample cell, we performed very sensitive isotope-selective measurements on CO2. Detection limits for 13CO2 of a few ppm and for the variation of the 13CO2 concentration of approximately 1 % were achieved.

THz Time-Domain Spectroscopy on Ammonia

The Journal of Physical Chemistry A, 2001

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Isotope-selective sensor for medical diagnostics based on PAS

Journal de Physique IV (Proceedings), 2005

Development of new optical sensor technologies has a major impact on the progression of diagnosti... more Development of new optical sensor technologies has a major impact on the progression of diagnostic methods. Of the permanently increasing number of non-invasive 13C-breath tests, the Urea Breath Test for detection of Helicobacter pylori is the most prominent. However, many recent developments go beyond gastroenterological applications. We present a new detection scheme for breath analysis that employs an especially compact

High Precision Measurements of Atomic Level Splittings by Means of Periodic Pumping with Picosecond Light Pulses

Laser Spectroscopy VI, 1983

Cascade Free Lifetime Measurements by Laser Excitation of Foil- or Gas-Excited Beams

Retraction Watch

I presented an alternative concept for the carbon cycle, which different to the IPCC mainstream a... more I presented an alternative concept for the carbon cycle, which different to the IPCC mainstream also includes time and temperature dependent variations in the natural emission-absorption cycle of CO2. We have many indications that the various mechanisms, along with their dependence on temperature and other environmental properties have not remained constant during the pre-industrial era. This inconsistency invalidates the fundamental assumption, that natural emission and absorption during the pre-industrial period did remain constant. Even less this is valid over the industrial era, a period which is characterized by the IPCC as the fastest rise in temperature over the Holocene or even the last interglacial. Science always has to question if the assumptions on which a theory is based, are reliable, and this cannot be decided by voting or by religion, only by facts and arguments which are in agreement with all physical laws.

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Optical cooling of trapped ions by self-induced Zeeman coherence

Trapped ions are widely discussed as candidates for new frequency standards. For this, such effic... more Trapped ions are widely discussed as candidates for new frequency standards. For this, such efficient cooling of the ion motion which limits the ultimate resolution is required and has successfully been achieved by optical sideband cooling.1,2 Here we discuss a new approach to the cooling of ions in a Paul trap, which is based on self-induced Zeeman coherence in conjunction with optical pumping.

Thz Studies Of Rotational Line Shapes

QELS '97., Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 1997

significant in the confined systems. Second, the faster dipole relaxation, which has been associa... more significant in the confined systems. Second, the faster dipole relaxation, which has been associated with hydrogen bond formation, is of the same order in size as the b u k however, as seen in Fig. 2, this contribution is of increasing importance in smaller micelles. Finally, both relaxation processes observed here are faster in the confined systems. *Present address: Rice University, ECE Dept., MS366, 6100 Main St., Houston, Texas 77005; E-mail: daniel@rice.edu **Present address: Rice University, Chemistry Dept., MS60, 6100 Main St., Houston, Texas 77005; E-mail: colvin@ruJrice.edu

Optical pulse train interference spectroscopy with an injection laser

We report on the use of ultrashort light pulses from an injection laser for extremely accurate le... more We report on the use of ultrashort light pulses from an injection laser for extremely accurate level splitting measurements in atoms. Use of optical pulse train interference spectroscopy (OPTIS)1,2 allows resolution of the well-known hyperfine splittings of the Rb and Cs ground state comparable with the best rf experiments published so far. We can observe resonance widths for 10-GHz splitting frequencies down to 50 Hz and measure small frequency shifts which are due to buffer gases. These results are obtained with a pure optical excitation and detection scheme.

Systematic studies of ion motion in a Paul trap by means of self-induced coherences

Tunable ultrashort pulse generation with a fiber grating Raman laser

Terahertz coherent transients from N 2 O vapor

An experimental and theoretical study of coherent THz transients is reported. Compared to coheren... more An experimental and theoretical study of coherent THz transients is reported. Compared to coherence effects for nuclear and electron spin systems, the work reported here involves samples many wavelengths in length, so that in addition to the point response, propagation effects are also important. In contrast to infrared and optical investigations, where coherent transients are detected as pulse intensities or as beat notes on a carrier, our experiments directly measure the actual electric field of the transmitted radiation pulse and that radiated by the N2O vapor sample.

High Precision Level Splitting Measurements with Picosecond Light Pulses from an Injection Laser

Coherence and Quantum Optics V, 1984

Modulated pumping1, 2 is a well-known principal in high-resolution spectroscopy and can be used t... more Modulated pumping1, 2 is a well-known principal in high-resolution spectroscopy and can be used to create atomic coherence between close lying or even degenerate atomic or molecular states and allows to measure energy splittings between adjacent states3. In this context the possibility of optical pumping by a periodic pulse train has been mentioned by several authors4. So far, however, its potentiality and ability for quantitative measurements has only scarcely been employed.

Observation of 517 Ghz Fine Structure Quantum-Beats in Na

Methods of Laser Spectroscopy, 1986

The feasibility of time-resolved coherence spectroscopy for measurement of atomic level splitting... more The feasibility of time-resolved coherence spectroscopy for measurement of atomic level splittings with frequencies up to the THz-range is demonstrated in this contribution. For the first time quantum-beats, which are due to the fine structure splitting of the first excited electronic state in Na, have been measured. With a beat frequency of 517 GHz this is the fastest quantum-beat signal observed so far.

OBSERVATION OF COMPLETE POPULATION TRAPPING IN AN EXCITED STATE OF Yb IONS

Ion traps are of current interest for high precision measurements of atomic splitting frequencies... more Ion traps are of current interest for high precision measurements of atomic splitting frequencies and they are widely discussed as new frequency standards [1, 2]. Recently they have also successfully been used to perform quantum jump experiments [3, 4]. The ion storage technique can successfully be applied to observe ions for long periods without perturbations and thus to eliminate transit time broadening and collisional effects. We were interested to make high resolution level splitting measurements with Yb ions which are proposed as a proper candidate in ion trap frequency standards [1]. When resonantly exciting the ions to the 6p2P1/2-state we measured a rapidly decreasing fluorescence signal. In order to explain this phenomenon we have investigated the excitation scheme of Yb+ in more detail (see Fig. 1).