This is a fascinating question and is very complicated to answer, and depends on quite a few factors. The things I will attempt to cover in this answer are:

What would soil look like?

What will happen to cities?

What would the atmosphere look like immediately after the glassing occurs?

Answering this question does require a few assumptions, and for the sake of simplicity I will take everything you say at face value. I am working on the assumption that by the weapon's temperature you mean how hot the target becomes. I will also assume that in "land that can hold infrastructure" you include largely uninhabited areas, like deserts and arctic regions.

The first dependency is whether 3,000 degrees is in fahrenheit or celcius. The result will depend heavily on which measurement is being used, and I will try to include both. It does also depend on how long the weapon remains on the target, I will assume long enough to heat everything until the bedrock up to 3,000 degrees, also accounting for fahrenheit and celcius.

For the sake of my own time (and sanity) I won't be going into every aspect of it, and as of writing this it took me roughly an hour to just figure out what clay would look like post-glassing.

If I don't cite a source, it was something I could figure out through a few google searches (I'm not saying that to be demeaning, this still took a long time and I fully do not blame you for asking instead of doing this yourself)

Now for the actual answer:

When it comes to soil, this actually depends on 3 things itself: the composition in amounts of clay, silt, and sand.

Clay first: the chemical composition of clay is such that when it is heated to ~1,200 celcius, or ~2,200 fahrenheit during the firing process, it shrinks and releases H2O into the air. At ~1400 celcius or ~2250 fahrenheit, the most common type of clay (Kaolinite) will decompose into what is described as "mullite-like glass" (source 1), a cloudy white stone.

Now onto silt:

Seeing as silt is just eroded rock, I feel more confident in less in-depth research, along with the fact that saying exactly what silt would become is nearly impossible, and would be drastically different based on the precise location, so instead of focusing on the exact chemical composition of the rock like I had to do with clay (as I couldn't find any studies where they heated up clay to 3,000 degrees) I will simply focus on silicate rocks as a whole.

Thankfully (For the sake of my sanity) the heat of the lasers is enough to melt all silicates within rock at about 1200 celcius or 2200 fahrenheit (source 2). These would cool into extrusive igneous rocks, such as basalt or obsidian. Since obsidian requires near-instant cooling, it would mostly be slower cooled rocks like basalt or pumice, especially pumice considering that the melted soil would likely have a high water content (even more so in silty clay).

The final soil type is sand: sand is also made primarily of silicates, so would likely give glassy rocks such as trinitite, with a more greenish hue than the usual black landscapes.

Depending on the measurements, much of the ground would actually be vaporized. If it's in celcius, the boiling point of silicon is around 2900 celcius. It wouldn't be an explosion, but the lava would be boiling. If the measurement was in fahrenheit though, it would only be enough to melt, not vaporize. The vaporization of the stone would put countless deadly chemicals, including heavy metals, into the air, making it inhospitable to anything but the hardiest of microorganisms for decades, likely longer without extensive terraforming efforts.

Onto the next question, what would happen to cities:

For this I am going to assume the buildings are made similar to buildings on earth, made of concrete and steel. Concrete has a melting point of around 1500 celcius, or around 2800 fahrenheit, but it can go up to almost exactly 3000 fahrenheit, or 1650 celcius. the melting point of steel varies a lot depending on what kind, but all of them are under the temperature of the weapons provided. Given that, cities would essentially become large piles of melted concrete and steel.

The final question, the atmosphere:

Because of the fact that the given temperatures are more than enough to instantly combust any kind of organic matter, the soot that would enter the atmosphere would be akin to a nuclear winter. These are hypothesized to last several decades, so your colonists would likely have to wait quite a while before life can become sustainable for them. Considering the advanced technology required for glassing I don't doubt the ability to purify the air in whatever they live in, the issue would more be of electricity. With nothing to burn, and all previously existing rivers being reduced to slightly lowered divots of volcanic rock, and the sun being blocked out, electricity would be a huge concern. Anywho, back to the actual question-

The atmosphere would be largely unlivable for almost any sort of complex life, due to soot in the air and the toxic chemicals that would likely be released by the melting stone and burning plants. The temperatures would also likely remain dangerously hot for a very long time. It's also worth noting that despite the fact that oceans are not targeted in this scenario, the winter would decimate the oceanic ecosystem, just like it did after the chicxulub impact.

It really doesn't need to be said, but any permafrost the planet may have had is now gone. If the weapons targeted the arctic regions, then the ice was vaporized in moments. If they didn't, it was melted by the heat of the ground entering the atmosphere. Either way, all of the history and information that was stored in that ice, along with the CO2 and soot from past eruptions and such are all released into the water and into the atmosphere, acidifying the oceans even more with the worldwide fires and poisoning them with soot.

In conclusion:

Most of the planet would be black volcanic rock. Deserts could consist of more greenish rocks like trinitite. Areas with a high clay content would be more grayish. The atmosphere would be full of silt for decades, blocking out almost all light while also trapping in the heat from the lasers, keeping it dangerously hot for a long time, possibly for anywhere from years to decades. Cities would be turned to misshapen hills of concrete and steel. Life on land would be set back billions of years, likely only the hardiest extremophiles surviving. Any mining operations would be dangerous for months to years after the glassing while the lava cools. And the soot in the air would be very bad for the morale of any colonists. Even the oceans are mostly dead, collateral damage of the complete and total collapse of the energy cycle and poisoned by the fires and incinerated life across the world. Hope that answers your question!

Sources:

Source 1: Luo P, Tang Y, Li R, Ju M. Effects of Minerals Type and Content on the Synthetic Graphitization of Coal: Insights from the Mixture of Minerals and Anthracite with Varied Rank. Minerals. 2023; 13(8):1024. https://doi.org/10.3390/min13081024

Source 2: Melting Points of Rocks and Minerals. (n.d.). http://hyperphysics.phy-astr.gsu.edu/hbase/Geophys/meltrock.html