An electron of specific charge \( \frac{e}{m} \) enters an electric field, \( \vec{E} = -E_0 \hat{i} \) at a time \( t = 0 \) with an initial velocity \( \vec{v}_1 \). If \( \lambda_0 \) is its initial de Broglie wavelength, then its de Broglie wavelength at a time ‘t’ is