You have two options:
1. Thalys: high speed train, takes 1:45. You need to pre-book a ticket for specific date/time. Airline-style pricing. Assigned seats.
2. Intercity train: somewhat slower 2:25. You can buy a ticket and use on any train for the day the ticket is valid. Some discount if you book early. No assigned seats (train could be full if very busy, rarely happens)
Both can be booked on
https://treintickets.nsinternational.nl