A single slit of width $$a$$ is illuminated by a monochromatic light of wavelength $$600$$ nm. The value of $$a$$ for which first minimum appears at $$\theta = 30°$$ on the screen will be :

A

$$1.2 \ \mu$$m

B

$$3 \ \mu$$m

C

$$1.8 \ \mu$$m

D

$$0.6 \ \mu$$m