Astronaut Don Pettit was able to see a one watt laser pointed at the ISS from the ground by an amateur astronomy group. Two searchlights were directed at the Space Station intermittently while a laser was shone continuously, Pettit said he was able to see both.
宇航员唐·佩蒂特（Don Pettit）看到过一个业余天文学小组从地面对准国际空间站的一瓦激光。 佩蒂特说，他能够同时看见两个探照灯，间歇地对准空间站，同时不断发出激光。
He wrote about it…
Early Sunday morning, at 01:27 our time, the San Antonio Astronomical Association, an amateur astronomy group, succeeded in flashing the space station with a one-watt blue laser and a white spotlight as we passed overhead.
If you project a typical two-millimeter-diameter laser beam 400 kilometers, or 240 miles (the altitude of Space Station), the resultant beam diameter is about 1 kilometer. This has two significant impacts. First, precise tracking is needed to keep this 1-kilometer spot on the 200-meter cross-section of Space Station from a distance of 400 kilometers. This is no small feat, as the Station is a moving target in the sky.
如果发射的是典型的直径为2毫米的激光束，当它穿过400公里或240英里（空间站的高度），则所得的光束直径约为1公里。 这有两个重大影响。 首先，需要进行精确跟踪，以使这个1公里的范围能够覆400公里外的空间站200米横截面上。 这是一项不小的壮举，因为空间站是空中移动的目标。
Second, the intensity of the laser beam falls in proportion to its cross-sectional area. In this case, an initial beam of 2 millimeters expanded to 1 kilometer, reducing the intensity by a factor of about 250 billion. The rated output of the laser also will be reduced by this factor when viewed by the crew on Space Station, and so does not pose a threat to human eyesight. For the Space Station flash, the San Antonio astronomers used a one-watt laser and a gang of two 850-watt mercury-argon arc lamps. Both were clearly visible from my vantage point.
第二，激光束的强度与其横截面积成比例地下降。 在这种情况下，2毫米的初始光束扩展到1公里，从而使强度降低了约2500亿倍。 当空间站上的机组人员观察时，激光的额定输出也将减少此系数，因此不会对人类视力造成威胁。 对于能让空间站看到的闪光，圣安东尼奥市的天文学家使用了一瓦特的激光和两个850瓦特的汞-氩弧灯。 从我的角度来看，两者都是清晰可见的。
From Universe Today…
On March 4, about 65 amateur astronomers were in position at the Lazano Observatory in Springbranch Texas. They turned on the searchlights and waited as the ISS was set to make an appearance in the sky. At the precise time, they began flashing the two searchlights at a rate of two seconds on, then two seconds off, in a very non-technical, but effective manner.
3月4日，大约65名业余天文学家在德克萨斯州Springbranch的Lazano天文台就位。 他们打开了探照灯，等待国际空间站在空中露面。 在精确的时间，他们开始以非技术性但有效的方式，以两秒钟，然后两秒钟的频率闪烁两个探照灯。
“We had two people manually aiming the lights and two people holding plywood up over the lights, and they were manually tracking the space station,” Little told Universe Today.
Pettit, meanwhile, had no trouble seeing the flashes.
“Don sent us an email the next day,” Little said, “and he told us how bright it was, and how he could see the lights even before we started the flash system. He saw it from 10 degrees above from the west to 10 degrees from the Northeast.”
To everyone’s surprise, Pettit could also see the blue laser. “When the spotlights were off, he said he could still see the blue laser, which was shone steadily,” Little said. “I was pretty surprised that the laser light was that visible from space.”
令所有人惊讶的是，佩蒂特还看到了蓝色的激光。 利特尔说：“当聚光灯熄灭时，他说他仍然可以看到稳定发光的蓝色激光。” “我很惊讶激光在太空中是可见的。” 
The blue dot is the light directed at the ISS…
The view from the ground…
It’s worth pointing out that a 1 Watt laser is about 200 times as powerful as the standard, commercially-available laser pointer at 5 mW.
That is awesome! Especially the interaction between the astronaut and astronomers.
It’s not just the physics, which says it would be so. That we can seen, effectively, person-to-person, over such a distance, with such an expense to put the astronaut in space, and so little to flash a little laser light Is great!