Not necessarily 100% reflectivity. The sail may be thin enough to allow some light to pass through, thicker material may reduce the acceleration due to the mass increasing faster than the propulsive force increases. Thicker material may also increase the thermal absorption.

Thermal control can be performed in a variety of ways. An effective way is to adjust the laser energy directed toward the sail; too much and the sail melts, not enough and you lose valuable acceleration. Whiskers grown on the opposite side of the sail could aid in radiating away heat energy.

There have been several tests of solar sails, including on-orbit tests and an interplanetary test with the IKAROS, flown by Japan. Deployment and attitude control have been the main points of research, but as these are being worked out, actual propulsion tests seem to be the new phase of development.

As the article mentions in four sentences, Breakthrough Initiatives plans to test the idea of sending nanosats to Alpha Centauri in a flyby mission.

A little more detail here:
https://breakthroughinitiatives.org/News/4
“$100 million research and engineering program will seek proof of concept for using light beam to propel gram-scale ‘nanocraft’ to 20 percent of light speed. A possible fly-by mission could reach Alpha Centauri within about 20 years of its launch.”

As Robert stated, individuals are getting back into the business/hobby/charity of funding science. Many of our early observatories and telescopes were funded by individuals. As with rocketry and spacecraft, we Americans have grown weary of waiting for government to do what we want.

When you let government make all the decisions, they will do what they want, not what we want. Governments have a condescending attitude when it comes to their citizens; in the movie “The Giver,” the chief government official said, “When people have the freedom to choose, they choose wrong. Every single time.”

What government considers to be wrong is what We the People wanted in the first place. According to We the People, those for whom the government is supposed to work, the government chooses wrong. Every single time. Since government is supposed to represent We the People, it is we who are right, not the tyranny-aspiring government or its ruling class.

Power to We the People! Go Zuckerberg, Milner, and Hawking.

Maybe a light sail turns out to be impossible to make, but it is certainly worth trying until so has been concluded. Now it is open for research. Tiny probes might fly by the nearest star before this century ends.

Making the laser gun, the solar sail, and the payload.

Oh, wait. That’s what you meant.

Sure, if it’s not just an excuse to do nothing.

It strikes me as funny that those that imagine going to other stars consider mars colonization as too hard!

This is why we’ve been stuck going in circles for 50 years.

Perhaps non-reachable today, but once we are colonizing the Moon and Mars, wouldn’t it be nice to have something to aspire to?

Perhaps some believe it’s better to have a well funded non reachable goal?