Last year, with only a grainy, self-produced independent film to his credit (the watchable “Following”), Christopher Nolan exploded onto the film scene with the brilliant, critically lauded corkscrew noir “Memento.”

Telling the story of a semi-amnesiac patsy on a futile mission of revenge in a backwards-linear inversion of time and memory, Nolan created one of the most bold and acute syntheses of form and characterization since Orson Welles used his cinematic puzzle boxes to tell the story of Charles Foster Kane.

Nolan?s “Memento” grossed over $25 million, and convinced Warner Brothers to toss him the keys to “Insomnia,” a risky $50 million adaptation of a Norwegian psychological thriller starring Oscar winners Al Pacino, Robin Williams and Hilary Swank. It was a private screening of “Memento” that convinced Pacino to take the lead role in “Insomnia” as an ethically embattled cop whose sleep deprivation in Alaska?s perpetual daylight tragically clouds his judgment and memory as he attempts to track down the killer of a teenage girl.

The rapid emergence of a unique talent like Christopher Nolan, especially at a time when Hollywood conceives its movies mere branches on their sequoia-sized, ancillary-marketing juggernauts, is nothing short of remarkable.

Bunkered down all day in a San Francisco hotel, doing interview after interview to promote his imminent major studio debut, Nolan is the portrait of the exhausted English gentleman: soft-spoken, rumpled and erudite.

Nolan began making Super 8 films at the age of seven, and if nothing else “Insomnia” establishes Nolan as a born filmmaker, capable of executing his vision with or without a big budget.

“Overall, the process of moving from the smallest kind of film to something bigger has been reassuringly similar,” said Nolan. “Creatively, it?s still about figuring out what shots you need to tell the story.”

Nolan, who lists Hitchcock, Welles, Ridley Scott and Nicolas Roeg as his biggest influences, claimed that the jump from the self-financed “Following,” to the $5 million “Memento” was greater than the jump to the major studio-financed “Insomnia.” “There?s just an overall sense of an increased grind, and the shoot ends up going twice as long,” Nolan said. Principal photography on “Insomnia” lasted 54 days, compared to the 25-day “Memento” shoot.

Robin Williams is effectively cast against type in “Insomnia” as an unsettlingly banal murder suspect who enters into a relationship of manipulation and cooperation with Pacino?s cop. “Having cast Al Pacino as the veteran cop, you?ve created a very weighty iconic figure,” Nolan said, explaining his casting choices. “What we were looking for is someone who would be very striking in terms of balancing, someone who came from a very different angle.”

“When they first meet, you should be thinking, ?Why are these two guys together?? They?re not supposed to be together, and the conversation they?re having is totally unacceptable and weird.Having Robin Williams and Al Pacino on the screen … their whole star baggage just feeds into that feeling of inappropriate contact.”

Unlike Nolan?s previous films, “Insomnia” is constructed in fairly conventional, front-to-back fashion, although it does invoke the same questions of moral ambiguity and malleable memory and identity that ran through “Following” and “Memento.”

“In real life, the questions worth asking are the ones that are unanswerable,” said Nolan, addressing the often-perplexing nature of his films. “To me, it?s pointless to construct a pretend miniature model universe in which you can answer those questions. I?m much more interested in constructing something that has a little more reality as I perceive it, and therefore some of those questions are left hanging, because I can?t answer them.”

In adapting the 1997 Norwegian thriller “Insomnia” (which starred Stellan Skarsgaard in the Pacino role), the British-born Nolan sought to transform the material by making it into “a very American film.” The Alaskan locale was a key component in articulating this vision.

“Alaska is sort of the last frontier, and it is a very uniquely American place,” said Nolan. “What you have in Alaska is small towns full of people from all over the country who come there for all kinds of different reasons, so it?s an oddly cosmopolitan place.”

All of Nolan?s films have dealt with themes of criminal behavior and moral relativism.

“We?re making a film that is concerned with the gray area between pragmatism and idealism,” Nolan said. “To me, that is fundamentally unanswerable, and that?s why it?s fascinating. And that?s why cop movies have forever referenced the gray area that cops operate in.”

“What I wanted to do, and what Al very much wanted to do, was to really delve into that, to create a movie that existed entirely in the gray area, and to really get dirty with it.”

“Insomnia” was scripted by rookie screenwriter Hillary Seitz, and it marks the first time that Nolan has directed from someone else?s script.

Asked about the adjustment, he said, “It was liberating in a lot of ways, because you?re able to just engage with the material as a director. You?re coming in to it at a later stage, so you?re given a quite effective, objective view of the material before you dive in. On the other hand, you inherit a lot of problems from somebody else?s brain.”

Nolan is currently working on a script about Howard Hughes for Castle Rock, which he intends to direct with Jim Carrey attached to star as Hughes. “This is a role that he has a passion to play,” Nolan said.

Considering the prospects of making another independent film just as his cerebral $50 million thriller is set to open on May 24, one week after “Attack of the Clones,” Nolan said, “I?d love to, but in a way, you can?t really go back. It?s never going to be the same. You?re never going to have nothing to lose.”