First of all, I think it is important to define what a laser is. LASER is anacronym that stands for Light Amplification by the Stimulated Emission of Radiation.

According to several online definitions a laser is: A device that creates a uniform and coherent light that is very different from an ordinary light bulb. Many lasers deliver light in an almost-perfectly parallel beam (collimated) that is very pure, approaching a single wavelength. Laser light can be focused down to a tiny spot as small as a single wavelength.

Laser output can be continuous or pulsed and is used in a myriad of applications. In other words, lasers typically emit only one color of light(one wavelength or frequency), and lasers often focus this light into a very narrow beam.

There have been a few studies investigating the effects of different types of lasers on the growth and physiology of plants. One study I found exposed plants to UV-B ultraviolet radiation in order to damage their tissues. The scientists then exposed the plants to either He-Ne (helium-neon) lasers or to normal red light radiation. They found that the plants exposed to the lasers repaired their tissues more rapidly and grew faster after being damaged by ultraviolet compared to the plants exposed to red radiation. This study indicated that certain lasers can help plants recover from damage by ultraviolet light.

Another study suggested that red laser light can increase the growth of rice stalks, while blue laser light stimulates flowering of rice and the production of grain.

Some scientists are now working to find combinations of blue and red lasers that maximize the yield (grain production) and growth rates of rice in a process called photonics.

In contrast, another view is that the high intensity light beams that lasers emit typically cause necrosis, or death, of plant tissues. In other words, if you shoot a laser at a plant, it will often leave a spot of dead plant tissue on the leaf where the laser energy contacted the plant.

Whether a laser harms a plant, assists its growth, or has no affect probably depends on a number of factors including the plant type, the tissue type (whether leaf, stem, root,etc.), the laser wavelength (or frequency), the laser intensity (number of photons per square cm per second), how focused or narrow the laser beam is, and the duration of time for which the plant is exposed to the laser.

I am not sure what studies have looked at the effect of lasers on plant growth through different objects.

I am not sure how much is actually known about how lasers effect the growth of plants through different objects. I do know that how lasers effect growth of both plants and animals is being studied. Lasers are even used for different types of surgeries these days which makes the knowledge of any effects including growth of cells very important.

There is new research underway about the effects of light emitting diodes (LEDs) on cell growth. LED's can give off light in the near-infrared (a longer wavelength than the red that we see) which can penetrate more tissue --useful for photo(light) therapy. If you were to hold a flashlight into the palm of your hand and you look at the light coming out, you would notice it looks red. This is because of the colors that we see only red light makes it all the way through (the other colors are absorbed).