"no further doubts" is a correct and usable phrase in written English.
You can use it when you are certain about something and you want to make it clear that there is no room for doubt. Example sentence: After completing my research, I have no further doubts that the theory is correct.
But if the report of his promotion to the No. 2 post on the National Defense Commission is true, they said Wednesday, there can be no further doubts.
He left no further doubts as to his position when he elevated his son Honorius to Augustus in January 393 and thereby demonstrated that he would no longer tolerate any emperor other than himself and his sons.
Next, debriefing consisted of the application of the questionnaire to 6 individuals similar to the population under study, at which point the degree of understanding of each of the questions was assessed until there were no further doubts.
"No further doubt is possible.
If this choice were not clear already, the impending cap-and-trade legislation likely to pass the U.S. House this summer should leave no further doubt.
"The news created quite a jubilee among the governor's friends on board the train, who congratulated him on his being able to enter the capital of the nation as the actual president-elect, with no further doubt resting upon his title to the office".
The Thessalians, being bereft of their allies, did thereupon take the Persian part whole-heartedly and with no further doubt, so that in their acts they approved themselves men most useful to the king. 1 Cp.
Our observation casts further doubt over Canright's generalization.
There is no further room to doubt that Vladimir Putin definitely helped him win the election.
Recent data showed no outcome difference in patients with positive sentinel node between axillary dissection vs no further axillary surgery, raising doubts on the role of SLNB itself.
No further information being forthcoming, doubts were expressed both here and in America as to the accuracy of the observations, and Mr. McCook went to Texas in the summer of 1877 for the express purpose of testing them.
