N.J. Stat. § 40A:14-136
Leave of absence without pay may be granted by the authority in charge, to a member or officer of a municipal police department or force, in order that his services may be made available to the State or a county, or to a State or county department or agency. A request for a leave of absence shall be made in writing by the member or officer and the State or county, or the State or county department or agency, desiring his service, but no such leave of absence shall be used to displace an incumbent. Any such leave of absence shall not be for more than one year, but may be extended, in the same manner as originally granted, but in the aggregate, shall not exceed 5 years. Neither membership in the municipal police department or force, nor pension or retirement rights shall be affected by such leaves of absence, but pension contributions shall be payable notwithstanding such leaves of absence. Upon the expiration of any such leave of absence, the member or officer shall return to his original duties and resume his office, position or employment with the said department or force and be entitled to all salary adjustments, increments, seniority and pension rights, as if no leave had been granted.
N.J.S. § 40A:14-136