Bulk Damage Research Articles

Accurate measurements of laser-induced bulk damage density

The laser damage community has long been searching for the reproducibility of damage measurements in the nanosecond (ns) regime. Here we show that laser-induced bulk damage density of frequency conversion crystals can be measured with high accuracy and repeatability in the range from 2 to 20 ns. The rasterscan test procedure (Lamaignère et al 2007 Rev. Sci. Instrum. 78 103105), previously developed in order to determine laser damage density of large aperture UV fused silica optics, has been adapted to bulk damage measurement. The large volume scanned during tests permits us to measure very low damage densities. For smaller optical components, small volumes are tested using the normalized 1/1 test procedure. Whatever test procedures, accuracy and repeatability are obtained by means of a suitable data reduction. For comparison between different procedures, the classical damage probability plot has to be converted in terms of damage density. The consideration of error bars on damage site distributions is compulsory to compare experimental data. A special emphasis is put on damage detection tools. When tests are carried out on diverse facilities, pulse duration, spatial distribution and beam overlap are the key parameters which are to be taken into account to compare experimental data. We describe the equipment, test procedures and data analysis to perform these damage tests with small beams (Gaussian beams, about 1 mm @1/e, and top-hat beams). Other tests are realized with larger beams (cm sized) which are compared with small beam results. The consistency of all the results gives confidence in the measurements. Reproducibility of measures is discussed in connection with current theoretical understanding of laser damage.

Degradation of high-resistivity float zone and magnetic Czochralski n-type silicon detectors subjected to 2-MeV electron irradiation

Particle-tracking detectors made on high-resistivity (HR) float zone (FZ) silicon are widely used in high-energy physics experiments. It is known that the incorporation of oxygen in the FZ Si can lead to some improvement in the radiation hardness of the material. In this contribution we investigate the effects of 2 MeV electron irradiation, up to a fluence of 5×10 16 e/cm 2, on the electrical and carrier lifetime properties of p-on-n silicon diodes fabricated on different substrate materials, including HR standard and oxygenated FZ, as well as HR magnetic Czochralski silicon, with a higher intrinsic oxygen contents. A progressive degradation of the characteristics is observed for all devices, pointing to a generation of bulk damage. Interestingly, a significant increase of the effective carrier concentration is observed after the highest fluences for all materials. Under the limited experimental conditions studied, no significant changes are observed for diode characteristics subjected to a thermal annealing treatment at 80 °C. This degradation in the electrical properties should be taken into account for the use of such HR Si materials under high-energy electron environments.

Ion bombardment of Fe-based amorphous metallic alloys

Fe74Cu1Nb3Si16B6 amorphous metallic alloy is investigated after ion irradiation by 110 keV N + and 593 MeV Au ions. The depth-profiles of the radiation damage were calculated by the SRIM2008 code. Applicability of transmission and conversion electron Mossbauer effect measurements to distinguish between the bulk and surface radiation damage is demonstrated by using different irradiation conditions. The investigated alloy is characterized by ferromagnetic interactions. The implantation does not depict appreciable changes of the samples’ surfaces. Changes in chemical short-range order (SRO) are revealed in N + irradiated alloys. Heavy Au ions caused pronounced effects in the position of the net magnetization though no impact on SRO was observed. After annealing, structural relaxation and annealing-out of the irradiation-induced stresses caused the rotation of the net magnetization back to its original position.

Bulk and surface laser damage of silica by picosecond and nanosecond pulses at 1064 nm

We measured bulk and surface dielectric breakdown thresholds of pure silica for 14 ps and 8 ns pulses of 1064 nm light. The thresholds are sharp and reproducible. For the 8 ns pulses the bulk threshold irradiance is 4.75 +/- 0.25 kW/microm2. The threshold is approximately three times higher for 14 ps pulses. For 8 ns pulses the input surface damage threshold can be made equal to the bulk threshold by applying an alumina or silica surface polish.

Influence of Terrestrial Cosmic Rays on the Reliability of CCD Image Sensors—Part 2: Experiments at Elevated Temperature

An aging effect in solid-state image sensors is studied: the generation of hard errors resulting in hot spots, warm pixels, or white pixels. This effect even occurs in image sensors that are simply stored on the shelf. The first paper described experiments that were set up to prove that the main origin can be found with neutrons that create displacement damage in the silicon bulk. These neutrons are part of terrestrial cosmic rays. This second paper is based on measurements done on devices that were stored on the shelf, but at elevated temperatures. In addition, annealing experiments were performed on packaged devices. The creation of these hot spots is independent of technology, architecture, sensor type, or sensor vendor, and it is observed in CCDs as well as in CMOS image sensors. However, the generation, and particularly the stability, of the hot spots seems to depend strongly on the storage temperature or on the annealing temperature.

The effect of material, thermal and laser conditioning on the damage threshold of type II tripler‐cut DKDP crystals

AbstractBy using the traditional temperature‐reduction method, KD2PO4 (DKDP) crystals were grown from 85%‐deuterated aqueous solution synthesized by different kind of KH2PO4 (KDP) raw materials. An experimental technique was employed to measure the variation of bulk damage threshold in plates of DKDP crystals. Bulk laser damage in unconditioned, thermal‐conditioned and laser‐conditioned type II tripler‐cut DKDP crystals has been studied using 1064 nm (ω) and 355 nm (3ω) laser at pulse lengths of 5ns, 5ns respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The energy coupling efficiency of multiwavelength laser pulses to damage initiating defects in deuterated KH2PO4 nonlinear crystals

The bulk damage performance of potassium dihydrogen phosphate crystals under simultaneous exposure to 1064, 532, and 355nm nanosecond-laser pulses is investigated in order to probe the mechanisms governing damage initiation during frequency conversion. The results provide insight into the dependence on laser parameters of the defect-assisted excitation process responsible for coupling of the laser energy into the lattice under exposure to high power laser light. In addition, it is suggested that the damage performance can be directly related to and predicted from the damage behavior of the crystal at each wavelength separately.

Pulse-duration dependency of femtosecond laser refractive index modification in poly(methyl methacrylate)

Refractive index modification of pure poly(methyl methacrylate) (PMMA) is investigated as a function of pulse duration using femtosecond lasers at 800 and 387 nm wavelength. It is observed that at 800 nm, the refractive index is modified more efficiently as the pulse duration decreases below 100 fs, whereas at 387 nm, efficient index modification is accomplished with longer, 180 fs pulses. Results suggest that three- and two-photon absorption is responsible for modification of pure PMMA at 800 nm and 387 nm, respectively. Repeated irradiation with short pulses of low laser fluence allows control of the photomodification via incubation, thus reducing bulk damage.

Evaluation of the Proton Induced Bulk Damage in SDRAM Utilizing 90 nm Process Technology

We describe proton induced bulk damage observed in 90 nm process SDRAM. The degradation of the data retention ability was evaluated. The effect due to the difference of process technology and memory cell structure was discussed. The result indicates that the value of the capacitance of the storage capacitor and the volume of the depletion region are key parameters concerning the failures caused by bulk damage.

Charge collection properties of Monolithic Active Pixel Sensors (MAPS) irradiated with non-ionising radiation

Monolithic Active Pixel Sensors (MAPS) have been proposed as sensing devices for the vertex detectors at the International Linear Collider (ILC), of the STAR upgrade and of the Compressed Baryonic Matter (CBM) experiment. These applications require substantial tolerance to non-ionising doses, which range up to ∼ 10 13 n eq / cm 2 . Intense studies were undertaken in order to measure the, so far widely unknown, radiation hardness of MAPS optimised for charged particle tracking and to identify the dominating effects of non-ionising radiation on these devices. This paper focuses on the recombination of signal electrons in the sensitive volume, which is the dominating problem provoked by bulk damage in MAPS. The dependence of this effect on some aspects of the pixel architecture is discussed, aiming to optimise the latter with respect to radiation tolerance.

Femtosecond laser-induced damage of gold films

Single- and multi-shot ablation thresholds of gold films in the thickness range of 31–1400 nm were determined employing a Ti:sapphire laser delivering pulses of 28 fs duration, 793 nm center wavelength at 1 kHz repetition rate. The gold layers were deposited on BK7 glass by an electron beam evaporation process and characterized by atomic force microscopy and ellipsometry. A linear dependence of the ablation threshold fluence F th on the layer thickness d was found for d ≤ 180 nm. If a film thickness of about 180 nm was reached, the damage threshold remained constant at its bulk value. For different numbers of pulses per spot ( N-on-1), bulk damage thresholds of ∼0.7 J cm −2 (1-on-1), 0.5 J cm −2 (10-on-1), 0.4 J cm −2 (100-on-1), 0.25 J cm −2 (1000-on-1), and 0.2 J cm −2 (10000-on-1) were obtained experimentally indicating an incubation behavior. A characteristic layer thickness of L c ≈ 180 nm can be defined which is a measure for the heat penetration depth within the electron gas before electron–phonon relaxation occurs. L c is by more than an order of magnitude larger than the optical absorption length of α −1 ≈ 12 nm at 793 nm wavelength.

Development of DAST crystals with high damage tolerance

We carried out the damage test of DAST crystals due to identify the causes of laser damages. DAST laser damages were classified into two regions; surface and bulk. The smooth surface tended to suppress the surface damage. As for the bulk, crystal defects such as twin boundary and narrow-line defect (NLD) were the main causes of bulk damages. Twin-free and NLD-free crystal showed high damage tolerance (over 2.8GW/cm2). Growing in the low-supersaturated solution and introducing the solution stirring were effective to obtain DAST crystals with high damage tolerance.

Influence of Terrestrial Cosmic Rays on the Reliability of CCD Image Sensors—Part 1: Experiments at Room Temperature

An aging effect in solid-state image sensors is studied: the generation of hard errors resulting in hot spots, warm pixels, or white pixels. These effects even occur in image sensors that are simply stored on the shelf. This paper describes experiments that are set up to prove that the main origin can be found with neutrons that create displacement damage in the silicon bulk. These neutrons are part of terrestrial cosmic rays. This statement is based on measurements done on devices that we stored on the shelf, that were flown around the world in airplanes, that were stored at high altitude, and that were stored in an underground laboratory. The creation of the hot spots is independent of technology, architecture, sensor type, or sensor vendor, and it is observed in charge-coupled devices as well as in complementary metal-oxide-semiconductor image sensors. In other words, it is a typical issue of the semiconductor base material: silicon! The paper is split up into two parts: this paper (part 1) describes the experiments done at room temperature, part 2 will concentrate on experiments done at higher temperatures.

Effects of Gamma and Heavy Ion Damage on the Impulse Response and Pulsed Gain of a Low Breakdown Voltage Si Avalanche Photodiode

Effects of displacement and ionization damage on the impulse response of a high-bandwidth low breakdown voltage Si Avalanche Photodiode was investigated using a picosecond laser system. Damage was generated using either Co60 gamma-irradiation or by scanning the device with an MeV ion microbeam. No shift in the impulse response characteristics and gain was observed for gamma doses as high as 100 kGy(Si). However, dark current measurements for irradiations with biases close to typical operating levels, exhibited enhanced ionization damage orders of magnitude higher than for no bias. Displacement damage introduced by the microbeam was used to differentiate between ionization damage in the guard ring isolation oxide and bulk damage. The absence of any marked change in the impulse response is discussed, as are possible mechanisms for the enhanced ionization damage

Radiation damage studies of detector-compatible Si JFETs

We have largely improved the performance of our detector-compatible Si JFETs by optimizing the fabrication technology. New devices feature thermal noise values close to the theoretical ones, and remarkably low 1/ f noise figures. In view of adopting these JFETs for X-ray imaging and HEP applications, bulk and surface radiation damage tests have been carried out by irradiating single transistors and test structures with neutrons and X-rays. Selected results from static and noise characterization of irradiated devices are discussed in this paper, and the impact of radiation effects on the performance of JFET-based circuits is addressed.

Numerical aperture dependence of damage and supercontinuum generation from femtosecond laser pulses in bulk fused silica

Competing nonlinear optical effects are involved in the interaction of femtosecond laser pulses with transparent dielectrics: supercontinuum generation and multiphoton-induced bulk damage. We measured the threshold energy for supercontinuum generation and bulk damage in fused silica using numerical apertures (NAs) ranging from 0.01 to 0.65. The threshold for supercontinuum generation exhibits a minimum near 0.05NA and increases quickly above 0.1 NA. For NAs greater than 0.25, we observe no supercontinuum generation. The extent of the blue broadening of the supercontinuum spectrum decreases significantly as the NA is increased from 0.01 to 0.08, showing that weak focusing is important for generating the broadest supercontinuum spectrum. Using a light-scattering technique to detect the onset of bulk damage, we confirmed bulk damage at all NAs studied. At a high NA, the damage threshold is well below the critical power for self-focusing.

Understanding and predicting the damage performance of KDxH2−xPO4 crystals under simultaneous exposure to 532- and 355-nm pulses

Laser-induced initiation of bulk damage sites in KDxH2−xPO4 crystals is investigated under simultaneous exposure to 532 and 355nm nanosecond laser pulses in order to simulate the operational conditions during harmonic conversion as well as probe the damage mechanisms. The results demonstrate synergetic damage effects under the dual-wavelength excitation. Furthermore, the damage performance is directly related to and can be predicted from the damage performance at each wavelength separately. The measured relative effective absorption coefficients at the two wavelengths are found to depend on the laser fluence.

Complex morphology of laser-induced bulk damage in K2H(2−x)DxPO4 crystals

We present a detailed study of the morphology of laser-induced bulk damage in K2H(2−x)DxPO4 crystals. We see three distinct regions of the internal damage sites: a rubble filled core, a shell that has probably been melted and compacted, and a larger outer region of slightly modified shocked material. The nature of these regions is important for understanding the impact of laser-induced damage on light scattering, which can be significant for high-power laser operation. We propose a simple model to explain the morphology and light scattering we observe.

Degradation induced by 2-MeV alpha particles on AlGaN/GaN high electron mobility transistors

We studied the degradation of AlGaN/GaN High Electron Mobility Transistors (HEMT) after 2-MeV alpha irradiation for two different fluences, namely 10 13 α/cm 2 and 10 14 α/cm 2. After the exposure and depending on the irradiation fluence, we observed a drop both in drain current and transconductance, and a reduction in the leakage current of the gate diode. We attributed these effects to bulk damage, radiation-induced formation of deep-level trap sites in the channel layer, and doping compensation/removal in the barrier layer.

Techniques for qualitative and quantitative measurement of aspects of laser-induced damage important for laser beam propagation

Characterizing laser-induced damage in optical materials is important for laser design and operation. Previous methods of evaluating optical materials damage resistance to high-power laser irradiation have typically suffered from shot-to-shot uncertainties in laser energy output and/or have insufficient sensitivity. More importantly, such methods do not address the aspects of laser-induced damage important to laser beam propagation, namely the amount of light scattered by the damage. We present a method for the quantitative correlation of material modification on the surface or in the bulk of optical materials to laser parameters, which deconvolutes the effects of laser output instability. In image analysis, two images, one a fluence spatial profile and the other a visible light scatter image of the damage, are directly compared to extract scatter as a function of fluence. An automated microscope is used to record the location and number of bulk damage sites and determine a calibration factor between the scatter signal observed and damage density. We illustrate the method with a determination of both bulk damage density as a function of laser fluence and of a representative size distribution in a DKDP crystal. Our method is capable of determining damage densities with an absolute uncertainty of ±0.3 pinpoint damage sites per cubic millimetre (pp mm−3) in the range 1–100 pp mm−3 with our minimum detectable density being 0.01 pp mm−3. We also determined the pps produced by laser pulses of 351 nm, 3 ns light to have a mean diameter of 5.5 ± 2.5 µm (1/e2).