Bruno Chassagne

Three-dimensional terahertz computed tomography of human bones

Three-dimensional terahertz computed tomography has been used to investigate dried human bones such as a lumbar vertebra, a coxal bone, and a skull, with a direct comparison with standard radiography. In spite of lower spatial resolution compared with x-ray, terahertz imaging clearly discerns a compact bone from a spongy one, with strong terahertz absorption as shown by additional terahertz time-domain transmission spectroscopy.

Terahertz tomographic imaging of XVIIIth Dynasty Egyptian sealed pottery

A monochromatic millimeter-wave imaging system coupled with an infrared temperature sensor has been used to investigate historic objects preserved at the Museum of Aquitaine (France). In particular, two-dimensional and three-dimensional analyses have been performed in order to reveal the internal structure of nearly 3500-year-old sealed Egyptian jars.

Photothermal converters for quantitative 2D and 3D real-time TeraHertz imaging

Recent advances for the measurement of TeraHertz (THz) radiation by using original IR temperature flux sensors are presented. The bolometer principle is used for designing simple thermal converters for THz radiations (measurement of the temperature increase of a sensitive absorber). Most of these sensors are efficient, sensitive and fast enough for quantitative measurement of THz source power as well as for 2D and 3D THz imaging. By combining optical and thermal technologies, we extend and adapt the use of thermal sensors to large THz wavelength till 3 mm (0.1 THz). A large variety of mono- or arrayed- thermal sensors is used and optimized for real-time room temperature THz imaging using adapted IR focal-plane microbolometers array (FPMA) camera. Optimisation and adaptation of such FPMA is discussed and a new arrayed prototype device of THz-Thermal Converter, “TTC”, for full-field real-time THz imaging is presented. This small size, low cost and efficient prototype design is discussed from the thermal point of view and is characterized using a compact powerful THz source. Their sensitivity is evaluated and the obtained 2D and 3D images clearly illustrates the high potential of this new kind of THz camera. Finally, it is shown that non-arrayed extended plane TTCs (EMIR sensitive screens) coupled to FPA cameras produce THz images free of diffraction phenomena.

Complex optical index of single wall carbon nanotube films from the near-infrared to the terahertz spectral range

We retrieve the complex optical index of single-walled carbon nanotube (CNT) films in the 0.6-800 μm spectral range. Results are obtained from a complete set of optical measurements, reflection and transmission, of free-standing CNT films using time domain spectroscopy in the terahertz (THz) and Fourier transform infrared (IR) spectroscopy in the visible-IR. Based on a Drude-Lorentz model, our results reveal a global metallic behavior of the films in the IR, and confirm their high optical index in the THz range.

Absolute self-calibrated room-temperature terahertz powermeter

Coupling optical and thermal properties of a terahertz (THz) thermal converter based on the Seebeck effect provides an unsupplied room-temperature measuring device dedicated to THz power metrology. Performance characteristics such as broadband response (0-30 THz), high sensitivity (<25 μW·Hz(-0.5)), and the possibility to develop an internal absolute self-calibration estimated at 9.93 W·V(-1) are reported. Advantages and drawbacks of this THz powermeter are discussed.

A Continuous Millimeter-Wave Imaging Scanner for Art Conservation Science

A monochromatic continuous millimeter-wave imaging system coupled with an infrared temperature sensor has been used to investigate artistic objects such as painting artworks or antiquities preserved at the museum of Aquitaine. Especially, 2D and 3D analyses have been performed in order to reveal the internal structure of a nearly 3500-year-old sealed Egyptian jar.

Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses

We demonstrate the advantage of combining non-diffractive beam shapes and femtosecond bursts for volume laser processing of transparent materials. By re-distribution of the single laser pulse energy into several sub-pulses with 25 ns time delay, the energy deposition in the material can be enhanced significantly. Our combined experimental and theoretical analysis shows that in burst-mode detrimental defocusing by the laser generated plasma is reduced, and the non-diffractive beam shape prevails. At the same time, heat accumulation during the interaction with the burst leads to temperatures high enough to induce material melting and even in-volume cracks. In an exemplary case study, we demonstrate that the formation of these cracks can be controlled to allow high-speed and high-quality glass cutting.

Dash line glass- and sapphire-cutting with high power USP laser

Glass cutting is a subject of high interest for flat panel display and consumer electronics industries. Among laser-based, water jet-based and diamond tool-based existing solutions, ultra-short pulses (USP) appear as a promising technology since this laser technology has the unique capacity to produce highly localized bulk modification owing to non-linear absorption. The cutting using USP lasers could be performed either by full ablation which is slow and generates a lot of dust, by controlled fracture propagation which is slow as well and may lead to path deviation, by stealth dicing which produces rough sidewalls, or by self-breaking induced by in-volume laser irradiation. The laser treatment is often continuous which is not necessary to perform glass cutting and may lead to over-exposure. In this paper we report on single pass glass and sapphire cutting using an USP laser (20W @200kHz or 8W@2MHz) using dash line laser treatment along the cutting trajectory. In-volume energy deposition was done along the glass thickness owing to a Bessel beam. The results will be discussed in terms of sidewall profile and roughness, path deviation, rim sharpness, energy dose and feed rate. Dash line treatment enables to tune the energy deposition and to produce the cutting effect but with a narrower heat affected zone, a better sidewall quality and a more accurate trajectory control of the cutting path.

Glass cutting using ultrashort pulsed bessel beams

Glass cutting is a subject of high interest in flat panel display and smart-electronics industries. The key issue is to combine high throughput, low residual thermal load and good sidewall quality. The process must be energy-efficient and material-efficient as well. Among laser-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology. Indeed, USP enables to produce internal modification owing to non linear absorption. Under specific irradiation conditions, this internal modification can lead to a free separation of the two glass parts.In this paper we report on recent investigations dealing with soda lime glass and Sapphire cutting using an USP Bessel beam. In fact, the long and uniform spot of zero-order non-diffractive Bessel beam can be turned into advantage in order to produce an elongated modification along the glass thickness (more than 1 mm long), and to achieve stealth dicing or controlled fracture propagation. The influence of pulse duration, pulse energy, and repetition rate will be discussed in terms of cutting feasibility, extend of heat affected zone and sidewall morphology. The results will be compared to those obtained with Gaussian beams under elongated-spot focusing conditions.Glass cutting is a subject of high interest in flat panel display and smart-electronics industries. The key issue is to combine high throughput, low residual thermal load and good sidewall quality. The process must be energy-efficient and material-efficient as well. Among laser-based and diamond tool-based existing solutions, ultrashort pulses (USP) appears as a promising technology. Indeed, USP enables to produce internal modification owing to non linear absorption. Under specific irradiation conditions, this internal modification can lead to a free separation of the two glass parts.In this paper we report on recent investigations dealing with soda lime glass and Sapphire cutting using an USP Bessel beam. In fact, the long and uniform spot of zero-order non-diffractive Bessel beam can be turned into advantage in order to produce an elongated modification along the glass thickness (more than 1 mm long), and to achieve stealth dicing or controlled fracture propagation. The influence of pulse duration, puls...

Ultrahigh wavelength range (300nm-2μm) polarization-independent 500gs/s single-shot pulse, all-optical real time oscilloscope

The development of ultra-broadband oscilloscopes is mainly governed by the needs of future telecom networks. But other applications are requesting the availability of true real-time acquisition oscilloscopes. Systems able to be used in single-shot operation are of prime interest for Inertial Confinement Fusion (ICF) and for the related R&D for plasma physics. We previously demonstrate a single-shot, 100GHz design of an all-optical sampling oscilloscope at 1μm (MULO). This laboratory system has been improved in stability and compactness to make an all-in-one box prototype. More, by the addition of an opto-electro-optics (OEO) sub-system at the input, we developed the ability to use this oscilloscope to analyze an electrical input signal up to 60GHz. This new integrated subset also increases the range of wavelength for optical input signal, from 300nm up to 2μm. Furthermore, it allows the use of inexpensive opto-electronic components at telecom wavelength for this system regardless of the signal to be analysed. In parallel with these improvements, by optimizing the heart of the system, we get a very high sampling rate, up to 500Gs/s and more; this allows considering much higher bandwidths in the future. In this talk, we will present latest developments and integration of this system. It will also allow us to give more details on the innovative OEO sub-system.