Best of 2011: How To Turn A Laser Into A Tractor Beam?

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Published by MIT

How To Turn A Laser Into A Tractor Beam

Physicists work out how to generate a backward pulling force from a forward propagating beam

A photon has a small momentum which it can impart to anything it hits, as Arthur Compton and Peter Lebedev discovered at the beginning of the last century. We now know that photons can be used to push anything from electrons to solar sails.

Today, Jun Chen from Fudan University in China and a few pals demonstrate the counterintuitive result that photons can pull things too. In other words, they've worked out how to generate a backward pulling force from a forward propagating beam.



Chen and buddies say this is possible when the system meets two conditions. First, it works only for beams in which the momentum in the direction of propagation is small, as is the case for beams that merely glance off an object. Second, the photons must simultaneously excite several multipoles within the particle, which scatter the beam.

If the scattering angle is just right, the total momentum in the direction of propagation can be negative, meaning the particle is pulled back towards the source and the light becomes a tractor beam.

This must not be confused with various "optical tweezer" type mechanisms in which particles trapped in a beam follow the intensity gradient of the light. In this case, the particles always reach some point of equilibrium where the intensity reaches a maximum.

Chen and co's new force works when there is no gradient. Given the chance, their tractor beam will pull a particle all the way back to the source.

That's a handy additional tool in the nanomanipulator's box of tricks. "This may open up new avenues for optical micromanipulation, of which typical examples include transporting a particle backward over a long distance and particle sorting," say Chen and co.

This is a theory paper so there's one piece of the puzzle left to fit. All they have to do now is demonstrate that their tractor beam works.

Ref: arxiv.org/abs/1102.4905: Backward Pulling Force From A Forward Propagating Beam

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What is the need for work and play means?

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The need for work and play

WORKABLE TIPS By PAUL KAM

Employers may not take too kindly to the current generation of employees who see a great need for work-life balance.

THE Human Resources manager looked up from the stack of papers in front of him and asked the young applicant why there was a gap from the time of his graduation and his work application. She took a few seconds to think before she gave a slight shrug and replied that she needed time and wasn’t sure of the jobs she wanted to apply for.

Then to justify her answer, she said that her mother financially supported her during that period.

The manager then asked her if she had any questions about the company since she had stated in her resume that she was looking “to grow her career and find the right company”.

An interviewer would be more impressed when a young applicant talks about her commitment towards her job instead of explaining the need for work-life balance.
 

She queried if it would be a nine-to-five job and added that she would not be able to work on weekends as she had church commitments.

I must say that she should not have responded in that manner as it was not appropriate.

This highlights the lack of drive and determination of the individual and raises doubts about the applicant’s commitment towards the job.



“Gap year” is a trendy term tossed around, and one commonly associated with the privilege of an affluent graduate. Indeed it means taking that fully financially supported time off for soul- or career-searching.

On the other hand, if the applicant had said she had taken the year off to gain working experience in the field she was planning to enter and to be sure that it was what she wanted, it would paint an entirely different picture.

In the present job market, employers are looking to hire people with more than just paper qualifications. Usually those who can afford to take a gap year to gain working experience and to determine their career path, would have an edge.

However, it has to be communicated in a manner that does not connote that a person has no direction or is not trying hard enough to look for a job and therefore making an excuse.

The other “demand” that interviewees tend to naively convey is work-life balance. This has to be earned and should not be considered a right of any new employee. In life, one needs to strike a balance.

Too much of one thing means less of another. Success is about hard work.

It is impossible to find an individual who has achieved success in the corporate world, or any other field by working regular hours, enjoying a five-day week and taking the contractual 14 or 21 days off to see the world.

Work-life balance should be considered a juggling act of the mind, and not the physical hours of work. In developed countries, there is great emphasis on work-life balance, so much so that some executives believe it is their right to demand that they work no more than eight hours a day, and yet be able to lead the lifestyle of many wealthy people.

I have been told by young travellers around the world about how they could afford to go on their journeys as there were apparently no limits to the number of credit cards they could obtain! However, recent surveys have also highlighted the number of bankrupts who were below the age of 30!

Having a work-life balance is not something that is totally unacceptable, but if I were in my 20’s and speaking to a prospective employer, I would keep my other priorities that are not work-related expressedly silent at the job interview. Employers are fair but like all human beings, they would like to believe that it is the job that is your most important priority at that point of time.

To me, work-life balance is not about equally distributing your time between work and personal life. It means being able to find the time to relax and do the things you love without compromising your work responsibilities.

I would also highlight to my employer of my objectives and goals for work life and social life and show how they complement each other. Find that balance and tailor your career for success.

Paul Kam is a lawyer by training. He has worked with private and public sector leaders and has designed and led several transformation, alignment and strategic change initiatives. With his understanding of market conditions in various industries, he is passionate about shifting and aligning mindsets and behaviours of leaders and employees. He is a member of the Malaysian Institute of Management and is also a certified team profiler and a life and wealth coach.

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All work and no play !

Beggars banned from French popular tourist hotspots

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Paris bans beggars from popular tourist hotspots

The Champs Elysées is one of three popular tourist and shopping areas in Paris decreed as no-go zones for beggars. Photograph: Alamy

The glittering Christmas window displays in Paris's luxury stores are often offset by a shivering person begging for coins nearby, huddled behind a cardboard sign saying "hungry".

French authorities have to decided to ban beggars from popular Christmas shopping streets and tourist hotspots over the Christmas period

Authorities in Paris have introduced a controversial ban on beggars in several parts of the French capital, in a move they say is aimed at protecting foreign visitors. Police have been ordered to arrest or fine 'aggressive beggars' in popular shopping locations and tourist hotspots.

The ban was first introduced on the Champs Elysée, intially from September until January, but has now been extended to next summer. Other no-go zones include the areas surrounding the Galeries Lafayette and Printemps department stores, as well as the Louvre museum and Tuileries Gardens.

The ban is said to target beggars organised by Mafia gangs. Three hundred cases of illegal activity, including fraudulent money making petitions, have already been reported over the past three months on the Champs Elysée.

The move has faced criticism from the Paris' socialist mayor, Bertrand Delanoë. He says it is a 'PR stunt' designed to stigmatise part of the population. He added that fighting poverty with repression and fines at such a time when the government is failing its own obligations to house vulnerable young people and provide emergency accommodation, is shocking.



Paris bans beggars from most popular shopping and tourist hotspots

French authorities claim no-go zones aim to stop pestering of foreign visitors by 'delinquents' run by criminal gangs 

By Angelique Chrisafis in Paris - guardian.co.uk

With the French economy in crisis and the looming spectre of another recession, Paris's poor and homeless people are more present than ever in doorways and metro entrances. Campaigners have demanded action on the country's housing crisis. Instead President Nicolas Sarkozy has launched a war on beggars, setting himself against Paris's popular mayor.

Sarkozy's interior minister and long-time right-hand man, Claude Guéant, has issued a series of decrees banning begging around Paris's most popular Christmas shopping and tourist spots. He says arresting and fining beggars is crucial to stop foreign visitors being pestered by begging "delinquents" run by organised mafia gangs.

The Champs Elysées was first on his list with a begging ban from September to January, which has been extended to next summer. Now two more Christmas begging no-go zones have been created: around the famous Galeries Lafayette and Printemps department stores, as well as the Louvre and the Tuileries Gardens.

Critics call it the latest round in Sarkozy's campaign against Roma and Gypsies. Guéant claimed that the anti-begging decrees were part of a "merciless fight" against "Romanian criminality".

He said Romanian criminals accounted for one in six appearances in Paris courts and half of those arrested were minors. The anti-begging policy targets practices such as collecting money for bogus petitions, said to be carried out by Roma girls and teenagers.

Guéant has contracted 33 Romanian police officers to help the Paris force round up beggars on the Champs Elyssés. He said of the 300 cases of illegal activity recorded in three months on the Champs Elyseés, almost all were Romanian nationals, adding that organised crime networks were "particularly cruel".

But the Socialist mayor of Paris, Bertrand Delanoe, France's most popular politician, called it a cheap "PR stunt" designed only to "stigmatise part of the population". He said: "Wanting to fight poverty by repression and fines is shocking at a time when the state isn't fulfilling its obligations in housing vulnerable young people or providing emergency accommodation."

He said Guéant was targeting some of the city's poshest areas while ignoring real problems in other neighbourhoods.

With four months until the presidential election, Sarkozy's party is prioritising security and crime in an effort to win back voters who have crossed to Marine Le Pen's extreme-right Front National.

Last year, Sarkozy caused international outrage when he linked immigration to crime and promised to expel Roma migrants and destroy illegal camps. The number of Roma in France has not changed since the destructions of the camps but NGOs warn they now live in greater poverty with a climate of fear and intimidation towards them.

Anti-begging decrees have long caused controversy in France, with one rightwing mayor outside Paris criticised in 2005 for a summer ban on homeless beggars because they "smelt offensive". Temporary anti-begging rules have been put in place in cities from Marseille to Boulogne, some challenged in court by human rights groups.

Guéant, recently dubbed "the voice of Le Pen" by the leftwing Libération, is also under fire for this latest promise to cut legal immigration to France, limiting the rights of non-EU graduates to stay in France after their studie