Praise be to Allah.
Whatever the Lawgiver has instructed us to leave alone of hair on the body, such as the beard and eyebrows, nothing should be removed from them, whether that is done whilst fasting or at any other time.
What we have been commanded to remove, may be removed as much as indicated by Islamic teaching, such as the armpit hair, pubic hair, and the moustache in the case of men.
Whatever has not been mentioned in the teachings is pardoned. That includes hair of the nose, chest, back, legs and forearms.
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
Removal of hair may be divided into several categories:
Hair which the Lawgiver has commanded us to remove, such as pubic hair, armpit hair and the moustache which we are commanded to trim.
Hair which the Lawgiver has forbidden us to remove: the hair of the beard. Plucking the eyebrows is also prohibited.
Hair concerning which the Lawgiver has not said anything, such as hair on the head, legs, arms and the rest of the body. With regard to that concerning which the Lawgiver has not said anything, some of the scholars stated that it is not allowed to remove it, because removing it is changing the creation of Allah, and changing the creation of Allah is something that is enjoined by the Shaytaan, because Allah, may He be exalted, tells us that he said (interpretation of the meaning): “and indeed I will order them to change the nature created by Allah” [an-Nisa’ 4:119]. Other scholars said that it is permissible to remove it, because nothing was said about it; sharee‘ah commands, prohibits and stays silent, and when it has stayed silent and said nothing, it is known that this is something that is neither enjoined nor prohibited, because if it was prohibited, sharee‘ah would have prohibited it, and if it was enjoined, it would have enjoined it.
The latter view is more likely to be correct, in terms of argument, because removing hair that it is not forbidden to remove is permissible.
End quote from Majmoo‘ Fataawa wa Rasaa’il al-‘Uthaymeen (11/205-206)
Please see also the answer to question no. 45557
Conclusion: with regard to removing hair from the body, what matters is whether the Lawgiver has given permission to remove it.
After that, it makes no difference whether it is done by laser or any other means of removing it.
The basic principle is that it is permissible to use a laser for that and for other permissible uses, unless trustworthy doctors state that the body may be harmed by that. In that case it is not permissible to use that which will cause harm to it.
Moreover, this matter has nothing to do with the fast at all, because fasting does not make it allowed or disallowed to remove hair whilst fasting, and the fast is not invalidated or enhanced by that. It has nothing to do with it.
But if a person removes any of his hair by way of sin and disobedience, then doing so in Ramadan is worse, because he should guard against sin and disobedience before he fasts by refraining from food, drink and physical pleasures.
Please see also the answer to question no. 14030
And Allah knows best.