Golay Cell Research Articles

Interferometer measurements of terahertz waves from Bi2Sr2CaCu2O8+d mesas

We fabricated rectangular mesa structures of superconducting Bi2Sr2CaCu2O8+d (Bi2212) using e-beam lithography and Ar ion beam etching techniques for terahertz (THz) emission. c-axis resistance versus temperature (R–T), current–voltage (I–V) characteristics and bolometric THz power measurements were performed to characterize Bi2212 mesas. The emission frequency of mesas was determined using a Michelson interferometer setup which also demonstrates polarized emission. Interference patterns of THz radiation from Bi2212 mesas were detected by various detectors such as a liquid helium cooled silicon composite bolometer, a Golay cell and a pyroelectric detector. An emitted power as high as 0.06 mW was detected from Bi2212 mesas. For the first time, most of the pumped power was extracted as THz emission from a Bi2212 mesa. The radiation at 0.54 THz was detected using the Michelson interferometric setup.

Experiment Studies on Two-Dimension Terahertz Raster Scan Imaging

In this article, two kinds of THz two-dimension raster scan imaging methods are investigated. An array scanning system, which uses a Pyrocam III camera as the detecting device, and a point-wise scanning system, which adapts a Golay cell as the detector, are designed and tested with imaging experiments. The speed, scale and quality aspects of the two systems are analyzed. The experimental results show the point-wise scanning system has higher contrast and precision performances, with a lower scanning speed, and it could be used to scan detailed small-scale textures. The array scanning system has faster scanning speed, with lower resolution, and it could be deployed for rapid, large-scale scans.

Performance of the continuous-wave imaging system based on a terahertz gas laser

Continuous-wave terahertz imaging was demonstrated based on an optically-pumped far-infrared gas laser and a Golay cell detector.The imaging system design and construction are discussed in the context of the choice and configuration of the involved terahertz optical components and devices.Performance characteristics of the system,including signal-to-noise ratio,spatial resolution,detector response and imaging speed were measured and analyzed in detail.With this system,terahertz transmission images of various samples were obtained,confirming the quality of our setup and supporting the feasibility of terahertz imaging technique for applications in security screening and quality control.A data processing method for automatic calibration of the image intensities in the background region was also proposed to remove the influence of laser power drift on the image quality.

A simple Fourier transform spectrometer for terahertz applications

A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors, sources, passive devices and materials in the terahertz (THz) range. It can be operated at frequencies between 0.3 and 1.5 THz, using a 50-μm-thick Mylar-film beam splitter. The spectral range can be changed by altering the thickness of the beam splitter. The highest frequency resolution is 750 MHz. We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers, direct detectors including an InSb semiconductor bolometer, superconducting tunnel junctions and the Golay cell, and sources including Gunn oscillators and a microwave source with its multipliers, as well as various materials and passive devices including Si wafers and metal mesh filters.

Terahertz Photometer to Observe Solar Flares in Continuum

Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with the well known microwaves component, bringing challenging constraints for interpretation. Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/s, smoothed for intervals larger than 4 s. For a 76 mm aperture, this corresponds to small solar burst intensities at THz frequencies. A system with 3 and 7 THz photometers is being built for solar flare observations on board of stratospheric balloon missions.

Uncooled detectors of continuum terahertz radiation

THz continuum spectral photometry has new and unique applications in different civil and military areas presenting a number of distinctive advantages on the well known microwaves or mid- to near-infrared technologies. THz sensing is essential to investigate the emission mechanisms by high energy particle acceleration processes. Technical challenges appear to diagnose radiation produced by solar flare burst emissions measured from space as well as radiation produced by high energy electrons in laboratory accelerators. THz filters and detectors have been investigated for the construction of solar flare high cadence radiometers to operate outside the terrestrial atmosphere. Experimental setups have been assembled for testing THz continuum radiation response from distinct detectors: adapted commercial microbolometer array, pyroelectric module, and opto-acoustic (Golay cell). The results permitted the final design of a THz double radiometer using Golay cells to be flown in stratosphere balloon missions.

Excitation wavelength dependences of terahertz emission from surfaces of InSb and InAs

The terahertz (THz) power radiated by the femtosecond laser excited semiconductor surfaces was measured by the Golay cell. Intrinsic InSb crystals as well as n- and p-type InAs were investigated by using three different wavelength, 780, 1030, 1550 nm, femtosecond lasers. It has been shown that p-type InAs crystal is the most efficient THz emitter for all three laser wavelengths with a nearly constant optical-to-THz power conversion efficiency of approximately 10−6.

Collimation Lens Design using AI-GA Technique for Gaussian Radiators with Arbitrary Aperture Field Distribution

The genetic algorithm (GA) is applied to the optimization of a sub-millimeter wave horn-lens collimation equipment operating at 150 GHz, and measurement is carried out to validate the performance of the optimized geometry. The aperture-integration (AI) method is employed to formulate the fitness function of GA in dealing with complex field distribution from an arbitrary radiation source. A diagonal horn and the auxiliary lens are fabricated according to the GA-optimized geometry, and their radiation properties are measured employing a BWO (Backward-wave Oscillator) with a golay cell terahertz detector. The measurement indicates that the gain and near-field beam radius conform to the values predicted by GA.

TYDEX: Optics for THz Photonics

TYDEX offers a wide range of optics for THz photonics: passive components (lenses, windows, prisms, mirrors, spectral and beam splitters, and waveplates), built up components (low pass and band pass filters, polarizers, and attenuators), and devices (Golay detectors)

Modeling of Infrared Gas Sensors Using a Ray Tracing Approach

Many gas molecules absorb electromagnetic radiation at characteristic wavelengths in the infrared region. This absorption can be used to identify defined substances like CO2, ammoniac, and so forth. A lot of different types of gas sensors are based on the principle of infrared absorption like photoacoustic sensors (e.g., Golay cells), dispersive infrared instruments (e.g., utilizing a diffraction grating), or Fourier transform infrared (FTIR) spectrometers. However, the most commonly used types of infrared absorbing gas sensors are nondispersive infrared (NDIR) sensors. Such a NDIR gas sensor consists of some basic function blocks, i.e., an IR-source, the sensor cell or optical path containing the sample gas, a gas specific filter, and an IR-detector. One of the central issues in the design of this kind of sensors is the geometry of the sensor cell. In this paper we investigate the use of statistic ray tracing to predict the efficiency of 3-D cell geometries for NDIR gas sensors. We demonstrate the feasibility of the method and show examples on how to apply it on given 3-D sensor models where we illustrate the agreement between simulated and measured gas response data.

SixGey:H-based micro-bolometers studied in the terahertz frequency range

SiGe-based bolometers originally designed for infrared operation have been tested as detectors of terahertz radiation. The obtained values of the responsivity and noise equivalent power show that these detectors can compete with conventional room temperature detectors such as pyroelectric detectors and Golay cells having an advantage in their compatibility with the CMOS technology.

Toward a 1550 nm InGaAs photoconductive switch for terahertz generation

We report a terahertz (THz) photoconductive switch made from a composite of metal ErAs nanoparticles embedded in In(0.53)Ga(0.47)As and coupled to a square spiral antenna. The THz output power was measured in a 77 K cryostat by using a standard hyperhemisphere-lens package, a Golay cell outside the cryostat, and a quasi-optical filter bank for spot frequency spectral measurements. Results indicate an average output power of approximately 12 microW at 22 V bias using 140 mW of optical pump power from a subpicosecond fiber mode-locked laser. In addition, the THz spectra displayed invariance to bias voltage despite operating near impact ionization.

Calculable blackbody radiation as a source for the determination of the spectral responsivity of THz detectors

The spectral responsivity of the detector is important for the layout and quantitative interpretation of spectroscopic experiments. In the terahertz (THz) spectral range the knowledge of the total (integral) responsivity of a detector, as well as its spectral distribution, is often insufficient. PTB determined the spectral irradiance responsivity of two THz detectors, a pyroelectric DLATGS detector working at room temperature and a silicon-composite bolometer working at 4 K, in the wavelength range from 62 µm (4.82 THz) to 1340 µm (0.22 THz) with temperature radiation from blackbody radiators. Our approach is to use two THz cavity radiators in combination with THz bandpass filters to provide calculable spectral irradiances, according to Planck's law of radiation, at several wavelength bands in the THz spectral range. One cavity radiator is working at an adjustable fixed temperature in the range from 15 °C to 90 °C while the other cavity radiator operates at LN2 temperature. The radiation of the two cavity radiators is alternately imaged on the detector via a gold-coated chopper wheel. Hereby the background radiation is cancelled and also the necessary modulation for the lock-in detection is provided. The cavity of the high temperature radiator is coated with a dedicated paint providing high wall emissivity in the FIR and THz spectral range to ensure true blackbody behaviour of the radiator. The bottom of the low temperature radiator consists of THz absorber foam providing hereby also nearly blackbody behaviour. All individual filters and, additionally, the employed filter combinations are characterized for their transmittance in the entire wavelength range from 0.8 µm to 1700 µm to obtain a precise knowledge of the transmitted blackbody spectrum. The very reproducible results indicate that this setup allows a fast, simple and reliable determination of the spectral responsivity of THz detectors. In a next step, the uncertainty of this technique will be further evaluated and investigations will be extended to other types of detectors (e.g. LiTaO3 detectors and Golay cells).

Linearity calibration of amplitude and power measurements in terahertz systems and detectors

We describe a device consisting of a set of silicon plates to be employed for calibrating the linearity of amplitude/power measurements of terahertz systems and detectors. The device is used to test a time-domain spectrometer, a pyroelectric sensor, and a Golay cell. The results demonstrate that the linearity of amplitude/power measurement cannot be assumed but must be experimentally verified.

Investigation of p-GaAsSb as a THz Emitter

Our purpose was to determine if GaAsSb might be made to emit THz-frequency electromagnetic radiation. Our result is that, with a suitable electric field imposed and under illumination by ultrashort pulses of near-infrared radiation, GaAsSb indeed emits THz radiation. To the best of our knowledge this is the first report of high-temperature-grown GaAsSb acting as a THz source. THz emission has been observed both by incoherent (pneumatic Golay cell) and by coherent (time-domain spectroscopy using electro-optic detection) experimental configurations. Both simple Ag paint and photolithographically formed Au on Ti antenna structures have been found to produce THz radiation. We compare our results with those from the better-known THz emitter, GaAs. In the case of GaAs, THz radiation is emitted even in the absence of applied bias. This is not the case for GaAsSb. We conclude that the photoconductive mechanism dominates in the emission of THz radiation from epitaxial single-crystal GaAsSb. A further proposal is made that such materials can be used with nanostructured surfaces for special THz-emission characteristics.

Low-Temperature Grown GaAsSb with Sub-Picosecond Photocarrier Lifetime for Continuous-Wave Terahertz Measurements

We report on continuous-wave optoelectronic terahertz (THz) measurements using low-temperature grown (LTG) GaAsSb as photomixer material. A broadband log-periodic antenna and a six interdigital finger photomixer with 1μm gap is fabricated on LTG-GaAsSb for THz generation and detection. At 0.37THz, the resonance frequency of the inner most antenna tooth, we obtained a power of 6.3nW. A Golay cell was used as detector. The photocarrier lifetime of the material was determined to be 700fs by pump-probe experiments with an optical wavelength close to the band gap of LTG-GaAsSb. The band gap was 1.0eV, measured by wavelength dependent pump-probe measurements.

A Simple Interferometer for the Analysis of Terahertz Sources and Detectors

The design and performance of a simple and compact far-infrared Fourier transform spectrometer is described. The spectrometer works as a Michelson interferometer without a beam splitter, and uses a Golay cell or a pyroelectric sensor for detection. A pair of flat lamellar mirrors with a computer-controlled displacement introduces a precisely defined phase difference between two parallel beams of nearly equal radiated power. The interferometer is intended for operation at frequencies between 0.1 and 3 THz with a frequency resolution of 6 GHz, and is used to characterize both continuous-wave and pulsed terahertz emitters, as well as different terahertz detectors.

From bolometers to beetles: the development of thermal imaging sensors

PurposeThis paper seeks to describe and discuss the historical development of IR sensors used in thermal imaging and to identify and consider some recent research trends.Design/methodology/approachThis paper first considers cooled semiconductor photon detectors and their limitations and then traces the historical development of un‐cooled IR sensing technologies and their commercialisation. It then discusses certain present‐day developments and research trends.FindingsThis paper shows that military‐funded research by the USA in the 1980s led to families of un‐cooled IR sensors, pyroelectric detectors and microbolometers, that have since been widely commercialised. Research continues in the search for a technology that can yield un‐cooled sensors offering the sensitivity of cooled devices, such as Golay cells, microcantilever arrays and biomimetics.Originality/valueThis paper traces the technological evolution of un‐cooled thermal imaging sensors and identifies and considers recent research.

A simple interferometer for the characterization of sources at terahertz frequencies

The design and performance of a simple and compact far-infrared Fourier-transform spectrometer for the characterization of sources is described. The spectrometer works as a Michelson interferometer without a beam splitter and employs a Golay cell or a pyroelectric detector. A pair of flat lamellar mirrors with a computer-controlled displacement introduces a precisely defined phase difference between two parallel beams of nearly equal radiated power. The interferometer is intended for operation at frequencies between 0.1 and 3 THz with a frequency resolution of 6 GHz, and is used to characterize both continuous-wave and pulsed sources.

Terahertz imaging: materials and methods

Terahertz (THz) imaging is rapidly developing. We present two new methods, based respectively on (a) a broadband thermal source (globar) and (b) a coherent, monochromatic source (optically-pumped THz laser). A room-temperature detector (Golay cell) is employed. Image quality is similar to that reported by others using more complex sources (quantum cascade lasers) and detectors (superconducting tunneling junctions).