O-FIB: far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment

Abstract

Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting “knife edge” is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (λ/40, with λ being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing.

光学频率梳技术与应用的 20 年发展回顾与展望

与展望

图片来源 iStock/yuyanga

撰文 |J.Z.

近期,两位NIST的学者,Tara Fortier和Esther Baumann在Nature旗下的《Communications Physics》对光学频率梳技术的原理,技术实现,应用和未来发展趋势进行了全面讨论。

点击这里查看原文

1

历史背景

光学频率梳的产生于人们对更加准确的时间基准和在此基础上的高精密测量技术的追求国际标准时间单位定义基于微波铯原子钟。其定义铯原子两个超精细能级间跃迁辐射9192631770次震荡所持续的时间为1秒。相比于微波原子钟,原子内对应于光学频率的跃迁可以作为比微波原子钟精度高出100倍的时间基准。

由于光波段和微波段巨大的频率差,传统方法需要大量多级振荡器链接起光波段频率与铯原子钟来实现光波段精密测量。基于锁模激光器的光学频率梳的出现使得仅使用单一系统既可快速简易的搭建起光学频率波段和微波频率波段之间的转换,使得微波时序信号得以直接从光学原子钟获取。

由于其产生过程涉及到非线性光学效应,光学频率梳可以进一步扩展到其他不同波段,其光谱覆盖范围可以从近红外波段一直到极紫外波段。因而光学频率梳的应用扩展到了许多不同的领域,诸如阿秒脉冲的产生,基于分子特征谱的气体探测,精密测距,分子光谱校正,以及光通信和精密测距。

2

光学频率梳基本原理

光学频率梳可简单理解为频率和相位稳定的锁模激光器。锁模激光器产生周期性的激光脉冲串。时间域内的周期性的激光脉冲序列转换到频率空间里,则可表示为包含了等间隔频率的光谱。该光谱的整体强度由激光秒冲的包络调节。因而在频率域其类似一把光学尺子,最小刻度等于锁模激光的重复频率frep(周期的倒数。尺子起点与零频之间有一定的差值f0 。这个差值由激光脉冲的载波和包络之间的相对相位来直接决定。因而,简单的描述光学频率可将其第N个频率VN表示为重复频率frep和f之和:

实际的锁模激光器的参数由于外界噪音干扰和激光本身功率不稳定等诸多因素是时刻在变化的。通过对激光腔长和内部介质的色散负反馈调节可以稳定住frep和f从而得到稳定的光学频率梳。其中对frep的测量相对容易可以直接通过光电器件完成,而f的直接测量一直到光纤技术发展到足以通过超连续过程将光谱展宽一个倍频才得以实现。

图1 光学频率梳的基本原理

3

光学频率梳光源的不同实现方法

光学频率梳光源的实现主要有两大类:一是基于锁模激光器实现的光学频率梳;二是基于微谐振腔和半导体激光器技术等实现的小型化和芯片级光学频率梳。

3.1 基于锁模激光器的光学频率梳

常规的通过稳频锁模激光得到的光学频率梳根据其所用的增益介质不同,主要分为基于晶体的固态系统光学频率梳和基于光纤的光学频率梳两类。这两类常规系统可以覆盖的波长范围从400纳米到4微米。其中商业化最为成功的光学频率梳是基于掺铒光纤系统的光学频率梳。对于其他极端波段的光学频率梳,例如从中红外波段到太赫兹波段,一般通过基于非线性光学过程的光学参量振荡器或者差频法去实现,这类方法产生的光学频率梳可达到27微米波长。而对于波长短于400nm的极紫外波段,光学频率梳的产生主要是通过腔增强的激光脉冲与惰性气体作用产生高次谐波,这里技术可以将光学频率梳延伸至11纳米。未来基于锁模激光器的光学频率梳的发展主要集中于实现高性能的同时 降低系统的尺寸重量和功率。

3.2 小型化和芯片级光学频率梳

基于半导体激光器的光学频率梳代表性的系统是通过量子级联激光器和锁模的垂直腔半导体激光器产生光学频率梳。而基于微谐振腔系统的光学频率梳则是通过非线性光学的四波混频过程将单频泵浦光展宽为光学频率梳。这两类系统目前是唯一有希望真正实现芯片级集成化光学频率梳的技术,但是其尚不成熟仍然面临诸多技术挑战,尚处于进一步发展中。其未来发展方向主要是进一步与光波导和半导体激光器集成化去发展出亚瓦级高性能并易于大规模制造的产品来满足实际应用需要。除此之外,基于相位调制单频激光的电光频率梳和基于超连续谱产生的光学频率梳也是两类重要的小型化光学频率梳光源。

图2 光学频率梳光源近些年的发展趋势

4

光学频率梳的应用

光学频率梳的应用大致可划分为两类:

第一类应用是以高精度测量为主,对光学频率梳各项技术要求极为苛刻,一般需要通过以原子钟为基准来完成,主要在实验室内完成。例如在绝对频率测量的应用中,光学频率梳可以用来测量光学原子钟的跃迁频率。由此推进的光学原子钟技术已经可以比现有的微波原子钟拥有更高的频率/时间分辨率。并且传统的微波原子钟发展已经进入平台期,难以有大大的突破,而基于光学频率梳的光学原子钟技术依然有较大提升空间。此外,光学频率梳通过对不同地区光学时钟的对比和同步,帮助建立全球光学时钟网络以及协助实现不同地区物理事件时间上的同步,这将有助于高精度测量的完成。其他领域的应用中,光学频率梳也被用于超低噪音微波频率产生以及天文光谱图像校正等等。

第二类应用主要是商业化应用,这类应用主要需要对变化的环境的稳健性要高,而对于光学频率梳的稳定性精确度要求降低。例如光学频率梳应用于光学雷达测距中,其测距的分辨率已经远远超过了传统光源,在平均时间为60毫秒下已经达到10纳米精度。不足之处在于目前的光学频率梳系统相对复杂昂贵,在商业应用上的研究集中于推进简单小型化低成本的光学频率梳系统的发展。此外,由于光学频率梳的宽光谱,高空间相干性以及高频率分辨率的特性,其在基于双光梳系统的光谱学应用中也取得了极大成功。

图3双光梳测距应用

5

光学频率梳的未来展望

光学频率梳未来发展主要集中在以下几个方面:

一是发展集成了便携式光学时钟的光学频率梳。这类光学频率梳将有助于建立新的全球时间基准。并且基于此类光学频率梳的洲际间的时间和频率转换将有助于获取高精度的测量大地水准面,从而促进基础物理的研究。

二是发展基于太空载体的光学频率梳。在太空运转的光学频率梳将有助于提高全球定位系统的精度以及促进大气光谱学的研究。同时基于太空载体的光学频率梳由于其低震动噪音的环境以及远离地球重力势能,将有助于实现精度超过10-19量级对基础物理量的测量实验。

三是发展新型量子光学频率梳。此类量子光学频率梳有助于解决非经典统计问题。

原标题:Nature – 通讯物理学(综述):光学频率梳技术与应用的20年发展回顾与展望

来源:中国光学

https://new.qq.com/omn/20200212/20200212A0CTR100.html

Green Industrial Revolution to Create 250,000 Jobs

t SHARE

Mark Powney , 18th November 2020

The Prime Minister has outlined his Ten Point Plan for a Green Industrial Revolution for 250,000 jobs

Covering clean energy, transport, nature and innovative technologies, the Prime Minister’s blueprint will allow the UK to forge ahead with eradicating its contribution to climate change by 2050, particularly crucial in the run up to the COP26 climate summit in Glasgow next year.

The plan – which is part of the PM’s mission to level up across the country – will mobilise £12 billion of government investment to create and support up to 250,000 highly-skilled green jobs in the UK, and spur over three times as much private sector investment by 2030.

At the centre of his blueprint are the UK’s industrial heartlands, including in the North East, Yorkshire and the Humber, West Midlands, Scotland and Wales, which will drive forward the green industrial revolution and build green jobs and industries of the future.

The Prime Minister’s ten points, which are built around the UK’s strengths, are:

  1. Offshore wind: Producing enough offshore wind to power every home, quadrupling how much we produce to 40GW by 2030, supporting up to 60,000 jobs.
  2. Hydrogen: Working with industry aiming to generate 5GW of low carbon hydrogen production capacity by 2030 for industry, transport, power and homes, developing the first town heated entirely by hydrogen by the end of the decade.
  3. Nuclear: Advancing nuclear as a clean energy source, across large scale nuclear and developing the next generation of small and advanced reactors, which could support 10,000 jobs.
  4. Electric vehicles: Backing our world-leading car manufacturing bases including in the West Midlands, North East and North Wales to accelerate the transition to electric vehicles, and transforming our national infrastructure to better support electric vehicles.
  5. Public transport, cycling and walking: Making cycling and walking more attractive ways to travel and investing in zero-emission public transport of the future.
  6. Jet Zero and greener maritime: Supporting difficult-to-decarbonise industries to become greener through research projects for zero-emission planes and ships.
  7. Homes and public buildings: Making our homes, schools and hospitals greener, warmer and more energy efficient, whilst creating 50,000 jobs by 2030, and a target to install 600,000 heat pumps every year by 2028.
  8. Carbon capture: Becoming a world-leader in technology to capture and store harmful emissions away from the atmosphere, with a target to remove 10MT of carbon dioxide by 2030, equivalent to all emissions of the industrial Humber today.
  9. Nature: Protecting and restoring our natural environment, planting 30,000 hectares of trees every year, whilst creating and retaining thousands of jobs.
  10. Innovation and finance: Developing the cutting-edge technologies needed to reach these new energy ambitions and make the City of London the global centre of green finance.

Prime Minister Boris Johnson said:

“Although this year has taken a very different path to the one we expected, I haven’t lost sight of our ambitious plans to level up across the country. My Ten Point Plan will create, support and protect hundreds of thousands of green jobs, whilst making strides towards net zero by 2050.

“Our green industrial revolution will be powered by the wind turbines of Scotland and the North East, propelled by the electric vehicles made in the Midlands and advanced by the latest technologies developed in Wales, so we can look ahead to a more prosperous, greener future.”

Welsh Secretary Simon Hart said:

“The Prime Minister’s announcement is hugely ambitious and will turbo-charge a green industrial revolution across the UK.

“With its established offshore wind, nuclear and electric vehicle industries, Wales is exceptionally well-placed to drive forward decarbonisation of energy, industry and domestic heating and be a centre for innovation in green technology like carbon capture.

“This means new investment and jobs across Wales as we level up the UK’s economy.”

To deliver on six points of the plan, the Prime Minister has announced new investment, including:

Carbon capture: To revitalise the birthplaces of the first industrial revolution, the UK will be at the global forefront of carbon capture, usage and storage technology, benefiting regions with industries that are particularly difficult to decarbonise.

An extra £200 million of new funding to create two carbon capture clusters by the mid-2020s, with another two set to be created by 2030. This increased the total invested to £1 billion, helping to support 50,000 jobs, potentially in areas such as the Humber, Teesside, Merseyside, Grangemouth and Port Talbot.

Hydrogen: Up to £500 million, including for trialling homes using hydrogen for heating and cooking, starting with a Hydrogen Neighbourhood in 2023, moving to a Hydrogen Village by 2025, with an aim for a Hydrogen Town – equivalent to tens of thousands of homes – before the end of the decade. Of this funding, £240 million will next year go into new hydrogen production facilities.

Nuclear: £525 million to help develop large and smaller-scale nuclear plants, and research and develop new advanced modular reactors.

Electric vehicles: Following extensive consultation with car manufacturers and sellers, the Prime Minister has confirmed that the UK will end the sale of new petrol and diesel cars and vans by 2030, ten years earlier than planned. However we will allow the sale of hybrid cars that can drive a significant distance without emitting carbon until 2035.

The UK car industry already manufactures a significant proportion of electric vehicles in Europe, including one of the most popular models in the world.

To support this acceleration, the Prime Minister has announced:

  • £1.3 billion to accelerate the rollout of chargepoints for electric vehicles in homes, streets and on motorways across England, so people can more easily and conveniently charge their cars.
  • £582 million in grants for those buying zero or ultra-low emission vehicles to make them cheaper to buy and incentivise more people to make the transition.
  • Nearly £500 million to be spent in the next four years for the development and mass-scale production of electric vehicle batteries, as part of our commitment to provide up to £1 billion, boosting international investment into our strong manufacturing bases including in the Midlands and North East.

This will help protect and create thousands of new jobs, particularly in the Midlands, North East, and North Wales.

We will also launch a consultation on the phase out of new diesel HGVs to put the UK in the vanguard of zero emission freight. No date has been set yet.

Homes and public buildings: £1 billion next year into making new and existing homes and public buildings more efficient and comfortable, extending the Green Homes Grant voucher scheme by a year and making public sector buildings greener and cutting bills for hospitals and schools, as part of the Public Sector Decarbonisation Scheme.

Low Carbon Industrial Strategy: A vision

The transition to a low carbon world will transform our whole economy. Lord Stern’s landmark Review in 2006 set out the economic case for action on climate change and for investment in a low carbon economy. Recognising that economic necessity, the UK has through the Climate Change Act become the first country in the world to adopt a legally binding target to reduce carbon emissions – by at least 26% by 2020 and by 80% by 2050.

UV Ozone production and destroy

UV light will create ozone from atmospheric oxygen at short wavelengths of less than 240 nanometers (nm). UV light will also destroy ozone and break ozone back down into atomic oxygen (O) and diatomic oxygen (O2) at wavelengths from about 200 nm to 315 nm. Therefore, the ozone layer does a great job filtering UV wavelengths from about 100 – 315 nm. This is important as these are the harmful wavelengths of UV light that cause sunburn, and DNA damage in living tissues.

Ozone generated from UV light

The ozone layer is an important part of our world’s stratosphere. The level of ozone in the stratosphere ranges from 2 to 8 ppm in the ozone layer, therefore most of the atmospheric oxygen remains in the diatomic form (O2).

Commercial Ozone Production from UV Light

The heart of every Ozone System is the Ozone Generator. Ozone (O3) is created from Oxygen (O2) in nature and also in Ozone Generators for commercial or industrial applications. However, Ozone (O3) quickly reverts back to molecular Oxygen (O2). Ozone cannot be stored due to a short half-life and must be produced on-site and on-demand. Therefore, the Ozone Generator is the most important component of any successful Ozone System.

Ozone can be produced commercially from an Ozone Generator using UV light. Ozone is produced from UV light wavelengths between 100 and 240 nm. A shortwave, low pressure UV lamp can be used for this purpose. These lamps will produce UV light with two peaks in the UV light band, one at 254 nm, and another at 185 nm. The 185 nm light is what is referred to as an “ozone producing” lamp, while the 254 nm light is referred to as a “germicidal” lamp.

Note: the 254 nm UV light is also used to break down ozone in air or water as UV light above 240 nm will photolyze ozone back to oxygen.

TiO2 optical constant

361.20 2.73000 0.02550
370.20 2.67700 0.01100
380.10 2.62800 0.00510
390.80 2.58100 0.00300
400.60 2.54400 0.00250
411.30 2.50900 0.00200
420.40 2.48300 0.00160
433.00 2.45300 0.00131
441.10 2.43800 0.00089
449.70 2.42300 0.00077
465.10 2.39900 0.00076
482.10 2.37700 0.00075
500.80 2.35700 0.00044
521.80 2.33800 0.00029
540.50 2.32400 0.00020
572.50 2.30500 0.00007
590.60 2.29600 0.00000
610.50 2.28700 0.00000
632.50 2.27901 0.00015
674.60 2.26700 0.00030
694.00 2.26300 0.00029
715.00 2.25800 0.00027
800.00 2.25000 0.00000
1000.00 2.25000 0.00000