Pub Date : 2017-05-22DOI: 10.1117/2.1201705.006868
M. Ott
Within Earth’s warming climate system, the dynamics of the cryosphere (i.e., the frozen part of the Earth’s surface) are vitally important. Indeed, the climate depends heavily on what happens at the planet’s poles. For instance, melting sea ice can affect the large-scale ocean circulation patterns that buffer climate extremes. In addition, melting glaciers and ice sheets cause the sea level to rise. To fully understand Earth’s rapidly changing climate, it is thus important to understand how and where ice is flowing, melting, or growing, and to investigate the global impacts of these changes. NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat2) mission1 (a follow-up from the ICESat mission, which flew between 2003 and 2009) has therefore been designed to study different forms of frozen water in a variety of locations (i.e., on land, fresh water, and seawater). The satellite (currently due for launch in 2018) will carry a single instrument, the Advanced Topographic Laser Altimeter System (ATLAS): see Figure 1. Whereas the Geoscience Laser Altimeter on ICESat had a single laser beam (with a 70m spot on the ground) and a distance between spots of 170m, the ATLAS spot size will be 10m and will have a spacing of 70cm. In addition, six beams will be used to measure terrain height changes as small as 4mm. The ATLAS photon-counting laser altimeter will thus enable frequent and precise measurements of elevation for monitoring changes in the cryosphere. In our work in the Photonics Group2 of the NASA Goddard Space Flight Center (GSFC), we have developed custom optical fiber arrays that are part of the ATLAS optoelectronic subsystems.3 The ATLAS pulsed transmission system consists of two 532nm lasers, along with transmitter optics for beam steering, a diffractive optical element that splits the signal into six separate beams, receivers for start-pulse detection, and a wavelength-tracking system. In addition, our optical fiber Figure 1. Two separate views of the Advanced Topographic Laser Altimeter System (ATLAS) being integrated onto the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) satellite at NASA’s Goddard Space Flight Center.
{"title":"Custom fiber optic arrays for climate studies","authors":"M. Ott","doi":"10.1117/2.1201705.006868","DOIUrl":"https://doi.org/10.1117/2.1201705.006868","url":null,"abstract":"Within Earth’s warming climate system, the dynamics of the cryosphere (i.e., the frozen part of the Earth’s surface) are vitally important. Indeed, the climate depends heavily on what happens at the planet’s poles. For instance, melting sea ice can affect the large-scale ocean circulation patterns that buffer climate extremes. In addition, melting glaciers and ice sheets cause the sea level to rise. To fully understand Earth’s rapidly changing climate, it is thus important to understand how and where ice is flowing, melting, or growing, and to investigate the global impacts of these changes. NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat2) mission1 (a follow-up from the ICESat mission, which flew between 2003 and 2009) has therefore been designed to study different forms of frozen water in a variety of locations (i.e., on land, fresh water, and seawater). The satellite (currently due for launch in 2018) will carry a single instrument, the Advanced Topographic Laser Altimeter System (ATLAS): see Figure 1. Whereas the Geoscience Laser Altimeter on ICESat had a single laser beam (with a 70m spot on the ground) and a distance between spots of 170m, the ATLAS spot size will be 10m and will have a spacing of 70cm. In addition, six beams will be used to measure terrain height changes as small as 4mm. The ATLAS photon-counting laser altimeter will thus enable frequent and precise measurements of elevation for monitoring changes in the cryosphere. In our work in the Photonics Group2 of the NASA Goddard Space Flight Center (GSFC), we have developed custom optical fiber arrays that are part of the ATLAS optoelectronic subsystems.3 The ATLAS pulsed transmission system consists of two 532nm lasers, along with transmitter optics for beam steering, a diffractive optical element that splits the signal into six separate beams, receivers for start-pulse detection, and a wavelength-tracking system. In addition, our optical fiber Figure 1. Two separate views of the Advanced Topographic Laser Altimeter System (ATLAS) being integrated onto the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) satellite at NASA’s Goddard Space Flight Center.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72794744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-18DOI: 10.1117/2.1201703.006624
M. Bradley, Anne Moore, N. Krstajić
One of the greatest challenges facing modern medicine is the inexorable rise of multidrug-resistant infections. In addition to better antibiotic stewardship, this challenge demands improved methods of diagnosis and treatment. Pulmonary diseases, which are responsible for a significant burden of disease and death worldwide, are among the conditions for which diagnosis must be improved. Little is currently known about the processes that drive lung disease. The ability to accurately diagnose and stratify patients would thus help clinicians overcome one of the main challenges presented by patients with severe respiratory diseases in the intensive care unit (ICU), and would help prevent the overuse of antibiotics. In conjunction with flexible bronchoscopy, which is routinely used in the ICU, microendoscopy can be used for in vivo examination of the lung. In this process, a narrow optical-fiber imaging bundle is inserted through the working channel of a bronchoscope, thus allowing images to be obtained from deep within the lung. Single-color confocal microendoscopy has previously been evaluated for distal lung imaging (generally with green fluorescence).1 Tissue autofluorescence will, however, often mask disease targets at this excitation wavelength (488nm). As a result, there is a pressing need to shift fluorescence microendoscopy into the red and near-IR region, where autofluorescence is much weaker. The lack of tools and approaches that can be used to interrogate the biology of the distal human lung in situ has been a significant hurdle in developing and evaluating new treatments of pulmonary infection and inflammation. Driven by this requirement, we are hoping to empower clinicians to perform a molecular optical biopsy with immediate bedside results. To this end, we are developing camera-based solutions2 that provide a robust and economical route to multicolor fluorescence detection. Our initial two-color widefield fluorescence microendoscopy system3 (see Figure 1) comprises off-the-shelf commercial components. Light from two LEDs (with center Figure 1. System diagram of our two-color fluorescence system. Two LEDs (with center wavelengths of 470 and 625nm) are combined with a dichroic mirror. Illumination from these LEDs is sent to the microscope objective via the emission filter and another two-band dichroic mirror. Fluorescence that is returned from the imaging bundle is then focused onto the color CMOS camera via a tube lens with a focal length of 200mm.
{"title":"Microendoscopy for molecular imaging inside the human lung","authors":"M. Bradley, Anne Moore, N. Krstajić","doi":"10.1117/2.1201703.006624","DOIUrl":"https://doi.org/10.1117/2.1201703.006624","url":null,"abstract":"One of the greatest challenges facing modern medicine is the inexorable rise of multidrug-resistant infections. In addition to better antibiotic stewardship, this challenge demands improved methods of diagnosis and treatment. Pulmonary diseases, which are responsible for a significant burden of disease and death worldwide, are among the conditions for which diagnosis must be improved. Little is currently known about the processes that drive lung disease. The ability to accurately diagnose and stratify patients would thus help clinicians overcome one of the main challenges presented by patients with severe respiratory diseases in the intensive care unit (ICU), and would help prevent the overuse of antibiotics. In conjunction with flexible bronchoscopy, which is routinely used in the ICU, microendoscopy can be used for in vivo examination of the lung. In this process, a narrow optical-fiber imaging bundle is inserted through the working channel of a bronchoscope, thus allowing images to be obtained from deep within the lung. Single-color confocal microendoscopy has previously been evaluated for distal lung imaging (generally with green fluorescence).1 Tissue autofluorescence will, however, often mask disease targets at this excitation wavelength (488nm). As a result, there is a pressing need to shift fluorescence microendoscopy into the red and near-IR region, where autofluorescence is much weaker. The lack of tools and approaches that can be used to interrogate the biology of the distal human lung in situ has been a significant hurdle in developing and evaluating new treatments of pulmonary infection and inflammation. Driven by this requirement, we are hoping to empower clinicians to perform a molecular optical biopsy with immediate bedside results. To this end, we are developing camera-based solutions2 that provide a robust and economical route to multicolor fluorescence detection. Our initial two-color widefield fluorescence microendoscopy system3 (see Figure 1) comprises off-the-shelf commercial components. Light from two LEDs (with center Figure 1. System diagram of our two-color fluorescence system. Two LEDs (with center wavelengths of 470 and 625nm) are combined with a dichroic mirror. Illumination from these LEDs is sent to the microscope objective via the emission filter and another two-band dichroic mirror. Fluorescence that is returned from the imaging bundle is then focused onto the color CMOS camera via a tube lens with a focal length of 200mm.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"553 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76065315","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-15DOI: 10.1117/2.1201702.006839
S. Boden, Xiaoqing Shi
An emerging lithographic technique offers a promising alternative to electron beam lithography for fabricating new semiconductor devices with both traditional and non-traditional resists.
{"title":"Helium ion beam lithography for sub-10nm pattern definition","authors":"S. Boden, Xiaoqing Shi","doi":"10.1117/2.1201702.006839","DOIUrl":"https://doi.org/10.1117/2.1201702.006839","url":null,"abstract":"An emerging lithographic technique offers a promising alternative to electron beam lithography for fabricating new semiconductor devices with both traditional and non-traditional resists.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"185 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72695869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-12DOI: 10.1117/2.1201702.006836
D. Marpaung
Radio-frequency (RF) filtering, an important signal-processing function in wireless communications, is used to separate an information signal from unwanted noise and interference. Traditionally, sharp and high-extinction electronic filters operating at a fixed central frequency are used to remove interference. This approach severely limits the flexibility of the system, however. In modern software-defined radios, where wireless systems are expected to share the RF spectrum, high-quality filters that are tunable over a wide frequency range are desired.1 These filters must meet a number of requirements, including wide-frequency tuning, high resolution, high suppression, and low insertion loss. Achieving all of these requirements with electronic filters is extremely difficult, however, as a result of their performance degradation when tuned over a large bandwidth. Microwave photonic (MWP) filters,2–4 a technology that uses a tunable optical filter to select RF signals that are modulated onto an optical carrier, represent an alternative approach that can readily achieve frequency tuning of tens of gigahertz with no performance loss. These filters face their own challenges, however. For one, their resolution is on the order of a few GHz, which is at least two orders of magnitude lower than that required for RF signal processing. Additionally, they suffer from trade-offs between resolution and filter suppression. Because of the losses that are associated with optical modulation and detection processes, MWP filters also suffer from a high insertion loss that can be prohibitive for real-world applications. Finding solutions to these challenges will lead to a unique signal-processing technology with wide-ranging applications, from wireless communications to radar and radio astronomy. In our work,5 we have focused on the development of MWP bandstop filters with all-optimized performance. These filters are free from any tradeoffs, and as a result, their tuning range, resolution, suppression, Figure 1. Conceptual steps toward building an ideal microwave photonic (MWP) bandstop filter based on stimulated Brillouin scattering (SBS).
{"title":"Building an ideal microwave photonic bandstop filter","authors":"D. Marpaung","doi":"10.1117/2.1201702.006836","DOIUrl":"https://doi.org/10.1117/2.1201702.006836","url":null,"abstract":"Radio-frequency (RF) filtering, an important signal-processing function in wireless communications, is used to separate an information signal from unwanted noise and interference. Traditionally, sharp and high-extinction electronic filters operating at a fixed central frequency are used to remove interference. This approach severely limits the flexibility of the system, however. In modern software-defined radios, where wireless systems are expected to share the RF spectrum, high-quality filters that are tunable over a wide frequency range are desired.1 These filters must meet a number of requirements, including wide-frequency tuning, high resolution, high suppression, and low insertion loss. Achieving all of these requirements with electronic filters is extremely difficult, however, as a result of their performance degradation when tuned over a large bandwidth. Microwave photonic (MWP) filters,2–4 a technology that uses a tunable optical filter to select RF signals that are modulated onto an optical carrier, represent an alternative approach that can readily achieve frequency tuning of tens of gigahertz with no performance loss. These filters face their own challenges, however. For one, their resolution is on the order of a few GHz, which is at least two orders of magnitude lower than that required for RF signal processing. Additionally, they suffer from trade-offs between resolution and filter suppression. Because of the losses that are associated with optical modulation and detection processes, MWP filters also suffer from a high insertion loss that can be prohibitive for real-world applications. Finding solutions to these challenges will lead to a unique signal-processing technology with wide-ranging applications, from wireless communications to radar and radio astronomy. In our work,5 we have focused on the development of MWP bandstop filters with all-optimized performance. These filters are free from any tradeoffs, and as a result, their tuning range, resolution, suppression, Figure 1. Conceptual steps toward building an ideal microwave photonic (MWP) bandstop filter based on stimulated Brillouin scattering (SBS).","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78135575","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-11DOI: 10.1117/2.1201701.006833
V. Rose, N. Shirato, D. Rosenmann, S. Hla
{"title":"Characterizing physical, chemical, and magnetic properties at the nanoscale","authors":"V. Rose, N. Shirato, D. Rosenmann, S. Hla","doi":"10.1117/2.1201701.006833","DOIUrl":"https://doi.org/10.1117/2.1201701.006833","url":null,"abstract":"","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"95 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87692708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-09DOI: 10.1117/2.1201702.006870
K. Strawbridge, B. Firanski, M. Travis
Tropospheric ozone, aerosols, and water vapor are important atmospheric constituents that affect air quality and climate. For instance, ozone is a short-lived climate pollutant that is photochemically active with nitrogen oxides, and its concentration in the troposphere can be significantly increased by stratospheric– tropospheric exchange events. In addition, aerosols contribute to the radiative budget, are a tracer for pollution transport, and they affect visibility, cloud formation, and air quality. Lastly, water vapor plays a pivotal role in climate change and atmospheric stability because it influences many atmospheric processes (e.g., cloud formation and photochemical atmospheric reactions). It is therefore important to measure the abundance of these atmospheric components in a synergistic way, to support the development of air-quality forecasts and diagnostic models. Such measurements can also be used for validating satellite observations that provide a regional to global perspective. Lidar (light detection and ranging) technology has rapidly advanced over the past several decades. From a number of different platforms, this technique can now be used to measure a variety of atmospheric constituents with ever increasing accuracy and at ever finer scales. Although the number of lidar instruments continues to increase worldwide, these platforms generally require an operator (particularly high-powered lidar systems).1, 2 To overcome the need for a lidar operator, our team at Environment and Climate Change Canada (ECCC) have previously designed several autonomous aerosol lidar systems3 to support a number of research objectives. For example, we have recently developed an autonomous mobile lidar system (see Figure 1) Figure 1. Photograph of the Autonomous Mobile Ozone Lidar Instrument for Tropospheric Experiments (AMOLITE) mounted in a climatecontrolled mobile trailer.
{"title":"Autonomous ozone, aerosol, and water vapor profiling of the atmosphere","authors":"K. Strawbridge, B. Firanski, M. Travis","doi":"10.1117/2.1201702.006870","DOIUrl":"https://doi.org/10.1117/2.1201702.006870","url":null,"abstract":"Tropospheric ozone, aerosols, and water vapor are important atmospheric constituents that affect air quality and climate. For instance, ozone is a short-lived climate pollutant that is photochemically active with nitrogen oxides, and its concentration in the troposphere can be significantly increased by stratospheric– tropospheric exchange events. In addition, aerosols contribute to the radiative budget, are a tracer for pollution transport, and they affect visibility, cloud formation, and air quality. Lastly, water vapor plays a pivotal role in climate change and atmospheric stability because it influences many atmospheric processes (e.g., cloud formation and photochemical atmospheric reactions). It is therefore important to measure the abundance of these atmospheric components in a synergistic way, to support the development of air-quality forecasts and diagnostic models. Such measurements can also be used for validating satellite observations that provide a regional to global perspective. Lidar (light detection and ranging) technology has rapidly advanced over the past several decades. From a number of different platforms, this technique can now be used to measure a variety of atmospheric constituents with ever increasing accuracy and at ever finer scales. Although the number of lidar instruments continues to increase worldwide, these platforms generally require an operator (particularly high-powered lidar systems).1, 2 To overcome the need for a lidar operator, our team at Environment and Climate Change Canada (ECCC) have previously designed several autonomous aerosol lidar systems3 to support a number of research objectives. For example, we have recently developed an autonomous mobile lidar system (see Figure 1) Figure 1. Photograph of the Autonomous Mobile Ozone Lidar Instrument for Tropospheric Experiments (AMOLITE) mounted in a climatecontrolled mobile trailer.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"4 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74183567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-08DOI: 10.1117/2.1201612.006785
Willie J Padilla, Christian C. Nadell
Most modern imaging systems function in a parallel acquisition scheme.1, 2 For example, the ubiquitous digital optical cameras of today employ arrays of pixels that each detect local light intensity, and simultaneously generate proportional electrical signals to construct an image. However, assembling the large quantities of detectors that are required for parallel imaging is not always feasible for other frequencies of light. In particular, there is a
{"title":"Metamaterial modulators enable new terahertz imaging techniques","authors":"Willie J Padilla, Christian C. Nadell","doi":"10.1117/2.1201612.006785","DOIUrl":"https://doi.org/10.1117/2.1201612.006785","url":null,"abstract":"Most modern imaging systems function in a parallel acquisition scheme.1, 2 For example, the ubiquitous digital optical cameras of today employ arrays of pixels that each detect local light intensity, and simultaneously generate proportional electrical signals to construct an image. However, assembling the large quantities of detectors that are required for parallel imaging is not always feasible for other frequencies of light. In particular, there is a","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"33 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90301820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-04DOI: 10.1117/2.1201612.006807
Z. Gan, Y. Chu, Xiaoyan Liang, Lianghong Yu, Cheng Wang, Yanqi Liu, Xiaoming Lu, Y. Leng, Ruxin Li, Zhi‐zhan Xu
The chirp-pulsed amplification (CPA) technique involves stretching and compressing a laser pulse in the temporal domain before and after amplification.1 Since this technique was first proposed in 1985, it has been used to successfully solve the problem of how to achieve ultrashort laser pulse amplification.2 In addition, the development of mode-locking lasers—particularly the advent of the self-mode-lock titanium-sapphire (Ti:S) laser— has allowed the duration of ultrashort laser pulses to reach the femtosecond (fs) domain.3 Since the 1990s, the Ti:S/CPA technique has thus been used to rapidly develop ultra-intense and ultrashort lasers. Theoretically, the amplified output energy of such lasers can be greatly improved with the use of large-aperture Ti:S crystals. When larger-aperture Ti:S crystals are pumped at higher pump fluence and energy, however, the transverse amplified spontaneous emission (TASE) and parasitic lasing (PL) within the booster-amplifier volume are easier to suppress than the amplified pulse energy.4 This is the main barrier to realizing high-energy Ti:S/CPA amplifiers, even as Ti:S crystals with increasing diameters are produced. At present, there are two main approaches to suppress transverse PL in these laser systems. First, the matched-index cladding (passive) technique can be used to increase the loss of spontaneous emission. In the second (active) technique, optimization of the time delay and lightly doped Ti:S crystals are used to control the transverse gain. To date, several countries have built petawatt-level ultra-intense and ultrashort laser systems (of which the focused intensity can be used to achieve 1021W/cm2) that are based on the Ti:S/CPA approach.5–7 Many Figure 1. Schematic diagram of the chirp-pulse amplification (CPA) experimental setup. Ti:S: Titanium sapphire. CW-SLM: Continuouswave single-longitudinal-mode. R.A: Regenerative amplifier. : Change in wavelength. amp: Amplifier.
{"title":"High-energy large-aperture titanium:sapphire chirp-pulsed amplification laser system","authors":"Z. Gan, Y. Chu, Xiaoyan Liang, Lianghong Yu, Cheng Wang, Yanqi Liu, Xiaoming Lu, Y. Leng, Ruxin Li, Zhi‐zhan Xu","doi":"10.1117/2.1201612.006807","DOIUrl":"https://doi.org/10.1117/2.1201612.006807","url":null,"abstract":"The chirp-pulsed amplification (CPA) technique involves stretching and compressing a laser pulse in the temporal domain before and after amplification.1 Since this technique was first proposed in 1985, it has been used to successfully solve the problem of how to achieve ultrashort laser pulse amplification.2 In addition, the development of mode-locking lasers—particularly the advent of the self-mode-lock titanium-sapphire (Ti:S) laser— has allowed the duration of ultrashort laser pulses to reach the femtosecond (fs) domain.3 Since the 1990s, the Ti:S/CPA technique has thus been used to rapidly develop ultra-intense and ultrashort lasers. Theoretically, the amplified output energy of such lasers can be greatly improved with the use of large-aperture Ti:S crystals. When larger-aperture Ti:S crystals are pumped at higher pump fluence and energy, however, the transverse amplified spontaneous emission (TASE) and parasitic lasing (PL) within the booster-amplifier volume are easier to suppress than the amplified pulse energy.4 This is the main barrier to realizing high-energy Ti:S/CPA amplifiers, even as Ti:S crystals with increasing diameters are produced. At present, there are two main approaches to suppress transverse PL in these laser systems. First, the matched-index cladding (passive) technique can be used to increase the loss of spontaneous emission. In the second (active) technique, optimization of the time delay and lightly doped Ti:S crystals are used to control the transverse gain. To date, several countries have built petawatt-level ultra-intense and ultrashort laser systems (of which the focused intensity can be used to achieve 1021W/cm2) that are based on the Ti:S/CPA approach.5–7 Many Figure 1. Schematic diagram of the chirp-pulse amplification (CPA) experimental setup. Ti:S: Titanium sapphire. CW-SLM: Continuouswave single-longitudinal-mode. R.A: Regenerative amplifier. : Change in wavelength. amp: Amplifier.","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78087986","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-05-03DOI: 10.1117/2.1201704.006895
N. Guan, X. Dai, J. Eymery, C. Durand, M. Tchernycheva
Nitride LEDs are coming to replace other light sources in almost all general lighting, as well as in displays and life-science applications. Inorganic semiconductor devices, however, are naturally mechanically rigid and cannot be used in applications that require mechanical flexibility. Flexible LEDs are therefore currently a topic of intense research, as they are desirable for use in many applications, including rollable displays, wearable intelligent optoelectronics, bendable or implantable light sources, and biomedical devices. At present, flexible devices are mainly fabricated from organic materials. For example, organic LEDs (OLEDs) are already being used commercially in curved TV and smartphone screens. However, OLEDs have worse temporal stability and lower luminescence (especially in the blue spectral range) than nitride semiconductor LEDs. Substantial research efforts are thus being made to fabricate flexible inorganic LEDs.1
{"title":"Nitride-nanowire-based flexible LEDs","authors":"N. Guan, X. Dai, J. Eymery, C. Durand, M. Tchernycheva","doi":"10.1117/2.1201704.006895","DOIUrl":"https://doi.org/10.1117/2.1201704.006895","url":null,"abstract":"Nitride LEDs are coming to replace other light sources in almost all general lighting, as well as in displays and life-science applications. Inorganic semiconductor devices, however, are naturally mechanically rigid and cannot be used in applications that require mechanical flexibility. Flexible LEDs are therefore currently a topic of intense research, as they are desirable for use in many applications, including rollable displays, wearable intelligent optoelectronics, bendable or implantable light sources, and biomedical devices. At present, flexible devices are mainly fabricated from organic materials. For example, organic LEDs (OLEDs) are already being used commercially in curved TV and smartphone screens. However, OLEDs have worse temporal stability and lower luminescence (especially in the blue spectral range) than nitride semiconductor LEDs. Substantial research efforts are thus being made to fabricate flexible inorganic LEDs.1","PeriodicalId":22075,"journal":{"name":"Spie Newsroom","volume":"75 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81204128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2017-04-25DOI: 10.1117/2.1201702.006825
R. Halir, A. Ortega-Moñux, P. Cheben, G. Wanguemert-Perez, J. Schmid, Í. Molina-Fernández
On-chip optical and photonic devices are key to major advances in fields as diverse as optical communications, sensing, and quantum physics. These integrated devices enable complex optical functionalities on a single chip (i.e., within a few square millimeters) that might otherwise occupy an entire optical table when implemented with bulk optical components. Currently, many commercial photonic chips are made from group III–V materials (i.e., containing elements in groups 13 and 15 of the periodic table), such as indium phosphide. Over the past decade, integrated photonic systems based on group IV materials—elements in group 14, particularly silicon and germanium—have drawn a lot of attention and are being developed by research groups around the world as well as industrial players, such as IBM and Intel. The main advantage of silicon photonics is that the CMOS infrastructure of the micro-electronics industry can be leveraged, potentially leading to high-volume and low-cost fabrication. However, in terms of performance and optical bandwidth—the range of optical wavelengths (colors) that a device can process accurately—many integrated photonic devices cannot yet compete with their bulkoptics counterparts. Here, we present a new silicon optical waveguide device that offers high performance and ultra-broad bandwidth operation with a very compact footprint. In photonic devices, the flow of light is governed by variations in refractive index, which engineers exploit in a range of materials to enable optical functionalities (e.g., for optical waveguides). In silicon photonics, the choice of materials is limited to silicon (with a refractive index n 3.5), silicon dioxide (n 1.4), and several polymers (n 1.6), which hinders the fabrication of high-performance, high-bandwidth devices. This limitation can be overcome using layers of materials with different thicknesses, which produce different Figure 1. A schematic representation of a new on-chip optical beamsplitter based on a nanostructured silicon multimode interference coupler showing the input (left) and output (right) light waves.
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