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Lochmann is a German surname, and a possible origin. However, Loughman is an Irish surname that goes back several centuries, so your ancestor may have replaced his existing name with a similar sounding Irish name. I think Lukmann is also a German surname though I'm not certain.
Loch means "hole" in modern German, though there appears to have been a similar word that meant "wood, copse". So your eponymous ancestor might have lived in a place where a hole was a prominent local feature; he might have made a living digging holes, e.g., a well-digger; or he might have lived or worked in a wood.
On the other hand if the original name was more like Lukeman, forget that lot and start again.