The beam gives unprecedented sensitivity to chemical analysis and allows researchers to create an hour-by-hour picture of what an individual has eaten.
They can even tell where a person has been by examining the chemicals which are in their hair.
Previous techniques had burned hair samples but the new method breaks them down instead and allows far more precise readings.
The researchers hope that it could be used for forensic science or by biologists exploring ruins - in theory they will be able to find out far more about the diet of ancient fossils they find.
Standard chemical analysis involves taking samples and putting them in mass spectrometers, machines which weigh and identify samples.
Until now lasers have been used to create the tiny 50 micron-wide samples but they scorch them because the beam is too powerful.
A team from U.S. Pacific Northwest National Laboratory got around the problem by using ultraviolet rays instead. Read More