Integrated nanostrip dipole antennas for coherent 30 THz infrared radiation

We report on the experimental study of infrared nanostrip dipole antennas which are connected to thin-film nanometer Ni-NiO-Ni diodes. The integrated Ni-NiO-Ni diodes are used to detect 30 THz (10 µm) CO₂-laser radiation.The diodes are deposited on 385 µm silicon substrates which are covered with a layer of 1.6 µm SiO₂ on both sides. We have found that in low-power applications 1.6 µm of SiO₂ yields excellent quarter-wave matching layers for wavelengths centered at ₀ = 10.8 µm. By this method 79% of the incident CO₂-laser radiation is transmitted into the Si substrate compared to 48% without SiO₂ layer. The use of SiO₂ quarter-wave matching layers considerably improves the efficiency of infrared nanostrip dipole antennas. This has been confirmed by the study of the laser-induced response of the Ni-NiO-Ni diode detectors as a function of the lengthL of the dipole antenna. Thus, we have observed that the laser-induced response strongly increases for shorter antennas and exhibits a distinct maximum atL=2.8 ± 0.3 µm. For the first time, we have investigated the 30 THz radiation patterns of nanostrip dipole antennas of different lengths. On this occasion, we have observed that the radiation pattern changes when the lengthL of the dipole antenna is varied. This observation indicates that antenna currents propagate on the nanostrip dipole antenna.     

Mixing of 30 THz laser radiation with nanometer thin-film Ni-NiO-Ni diodes and integrated bow-tie antennas

Mixing experiments with 30 THz CO₂-laser radiation as well as the detection of 35 ps 30 THz pulses of an optical-free-induction-decay CO₂-laser system have been performed with the first nanometer thin-film Ni-NiO-Ni diodes with a minimum contact area of 0.012 µm². Difference frequencies up to 85 MHz were detected by mixing two different CO₂-laser beams coupled to the diode with an integrated bow-tie antenna. The dependence of the beat signal on bias voltage, laser power and polarization of the infrared laser radiation was determined.     

Nanometer thin-film Ni-NiO-Ni diodes for mixing 28 THz CO2-laser emissions with difference frequencies up to 176 GHz

2 -laser emissions near 28 THz (10.7 μm) with thin-film nanometer-scale Ni-NiO-Ni diodes (MOM, MIM) connected to integrated bow-tie antennas and integrated rhodium waveguides. Difference frequencies up to 176 GHz were observed in mixing processes up to the fifth order by the addition of microwaves generated by a Gunn oscillator. The frequencies reported are up to a factor of 30 higher than those reported previously for thin-film diodes. The current–voltage characteristics of the diodes measured at radio frequencies correspond to their nonlinearity at frequencies in the mid-infrared. The integrated bow-tie infrared antennas show almost perfect polarization with respect to the incident radiation. The ratio of the polarized versus the cross-polarized signal amplitudes is over 34 dB. These results signify the extension of millimeter-wave and microwave thin-film techniques to the infrared. Received: 14 October 1997     

Frequency measurement chain to 30 THz using FIR schottky diodes and a submillimeter backward wave oscillator

An infrared frequency measurement chain is reported, the simplicity of which allows phase-coherent frequency measurements up to 30 THz. Frequency measurement is demonstrated on the 10P(28) line of the Lamb-dip stabilized¹³CO₂-laser.     

Extension of frequency measurements with Schottky diodes to the 4 THz range

The 11th harmonic mixing signals between a 386 GHz oscillator and a 4.25 THz laser with a signal to noise ratio of 25 dB in 100 kHz bandwidth have been obtained with a Schottky diode.     

Multi-color CARS for hydrogen-fueled scramjet applications

An approach to CARS, with considerable potential as a diagnostic for advanced airbreathing propulsion devices, is described and demonstrated. The technique is capable of providing simultaneous measurements of the major constitutents in H₂/air combustion. The method employs both broadband and narrowband Stokes beams to generate CARS via two, two-color and two, three-color wave mixing processes. Temperature and concentration information are simultaneously available from N₂, H₂, and H₂O. This permits the disappearance of fuel and appearance of product to be monitored. An analysis of the technique's capabilities and future improvements are discussed.     

Two-dimensional measurements of velocity using two rotating gratings

A two-dimensional vector velocimeter is proposed on the basis of the time-varying spatial filtering method using a rotating disk with two transmission gratings. The filtering characteristics of the spatial filter used in the velocimeter were studied theoretically. A preliminary experiment was performed to measure the velocity vector of a rotating random pattern. The experimental results show the usefulness of the present velocimeter for measurements of the velocity.     

A direct method of particle sizing based on the statistical processing of scattered photons from particles executing Brownian motion

A direct method of determining the mean diameter of particles executing Brownian motion is presented. The temporal coherence of the scattered field from submicroscopic particles illuminated by laser light is a function of both the integration time and the particle diameter. The temporal degree of coherence of the time-averaged scattered intensity decreases as the integration time increases. Statistical processing of the scattered photons leads to a method of particle sizing (average diameter), which circumvents the need for digital autocor-relation or power spectral estimation.     

An integrated optical sensor for measuring glucose concentration

We used an optical sensor combined with a Mach-Zehnder interferometric waveguide and optical fibers to measure slight changes of aqueous sugar concentrations. The merits of this sensor are simplicity, reliability, high sensitivity and continuous monitoring. The technique is based on the fact that the refractive index of sugar solution changes with the concentration of sugar. In the experiment, one arm of the interferometer is clad with glue and is thus isolated from the sugar solution. The other one is exposed to the sugar solution. A single mode fiber is directly glued onto the interferometric waveguide, to guide the light into the interferometer. If the concentration of sugar covering the waveguide changes, the phase of propagating light in the exposed arm will be changed, while the phase in the other arm is fixed. Hence the output intensity from the interferometer is directly related to the concentration of the sugar solution. The result of this experiment yields the relation between the sugar concentration and output signal. From 0% to 1% concentration of sugar solution, there is only a 1.4×10^–3 refractive index difference. Two sets of experimental data have been obtained, showing a linear relation between the sugar concentration and the output signal from our sensor. This sensor could be used for continuous monitoring of blood sugar in the human body.     

Two-Frequency waveguide CO2 laser for atmospheric pollution monitoring

The present paper suggests and discusses a method allowing one to produce a two-frequency switching mode between any two adjacent transitions of a CO₂ laser. Switching is achieved by means of simple modulation of the resonator length by a piezoelement. The use of conventional electronic circuits ensures the maintainance of a high power balance (10^–2–10^–1%) vs. switching rate) at the generation frequencies. The data of the two-frequency CO₂ laser with a waveguide resonator used for various systems, based on a differential absorption technique and designed to control the atmospheric pollutions, are presented.     

Principles and development of spatial filtering velocimetry

As one of the interesting optical techniques for measurements of the velocity, the spatial-filtering method is treated briefly in this review. The basic theory of the method is examined by analyzing the filtering characteristics of a spatial filter using the power spectral density function. The signal analyses are summarized as one of the techniques used in the spatial filtering method. Various configurations of the spatial filtering velocimeter are classified into typical four groups and outlined according to a variety of spatial filters employed in the velocimeters.     

Optical frequency counters

Realization of optical subharmonic generation enables us to devise various kinds of optical frequency counters. In contrast to the optical frequency measurement with a chain of servo-controlled oscillators, proposed optical frequency counters are composed of nonlinear optical components and amplifiers without using laser oscillators or frequency stabilization. It is possible to construct the proposed optical frequency counter by using available components of the present state-of-the-art in the visible and near-infrared region of the spectrum. Then a compact and universal frequency counter for optical oscillations will appear.Prof. F. P. Schäfer on the occasion of his 65th birthday.     

The ellipticity introduced by interferential mirrors on a linearly polarized light beam orthogonally reflected

Modifications of the state of polarization of a light beam trapped in a multipass cavity formed by interferential mirrors were studied. It was found that the mirrors analysed introduced ellipticities ranging from 3×10^–5 to 2×10^–4 per reflection.     

Measurement of the birefringence properties of the reflecting surface of an interferential mirror

We have set up an apparatus to measure the ellipticity acquired by a linearly polarized light beam after a single quasi-normal reflection on an interferential mirror. Results of measurements performed on a standard 10 cm diameter interferential mirror are presented.     

Achievement of laser fusion of biological cells using UV pulsed dye laser beams

This paper reports a successful achievement of laser-induced biological cell fusion using an excimer laser excited dye laser. To our knowledge, we examined for the first time the dependence of fusion rate on laser pulse energy, number of laser pulses, and laser wavelength. Maximum fusion rate of approximately 50% was obtained by this laser fusion technology.     

Rotational temperature and density measurements in a hypersonic flow by dual-line CARS

Rotational temperature and nitrogen number density are measured in the shock wave/boundary layer interaction region in the vicinity of a two-dimensional compression corner disposed in a low pressure, 55 K, Mach 10 hypersonic air flow. Spatially-resolved data are recorded using a nonlinear optical technique named dual-line coherent anti-Stokes Raman scattering (DLCARS). Averaged temperature and density profiles are compared with those predicted by a Navier-Stokes solver. Good agreement is found.     

A novel method of DNA transfection by laser microbeam cell surgery

A new technique is presented to incorporate exogeneous gene materials (DNA) into cells with a microbeam irradiation from an uv pulsed laser. A frequency-multiplied Nd:YAG laser, 355 m wavelength, 5 ns pulse duration, punches a self-healing hole of submicrometer aperture in cell membrane under selected irradiation conditions. It takes a fraction of a second for the aperture to close, long enough to allow the foreign DNA, contained in the medium, to slip into the cell. The method offers a clear advantage over existing methods: increases the success rate of DNA transfection as well as the efficiency of cell modification by orders of magnitude.     

Surface plasmon enhanced transient thermoreflectance

It is shown that optically excited surface plasmons can be used for measurements of the surface temperature of a metal with nanosecond time resolution. This method is closely related to transient thermoreflectance, but its sensitivity is considerably higher. We give a survey on the mechanisms involved, briefly discussing the dependence on the sample properties. Experimental confirmation of the proposed sensitivity enhancement as well as the time resolution is presented.     

First evidence for the linear magnetic birefringence of the reflecting surface of interferential mirrors

-9 . Received: 20 July 1998 / Revised version: 27 November 1998 / Published online: 24 February 1999     

Self-supporting thin-film beam splitter for far-infrared interferometers

Commercially available plastic films have been examined, in the spectral range up to 1200 cm⁻¹, for use as a beam splitter in far-infrared Michelson interferometers. The materials reported include polyethylene terephthalate, polycarbonate, polyvinylchloride, polypropylene, cellulose and polyethylene.