Trimedyne Executive to Leave Irvine Firm : Resignation: CEO Howard Cooper is credited for steering the maker of laser systems through its most tumultuous period.

In an unexpected announcement, Howard Cooper said Thursday that he is resigning as chief executive of Trimedyne Inc., the maker of medical laser systems, “to pursue other business opportunities.”

Cooper, who guided the company through the most tumultuous three years of its history, will remain as a consultant for one year. His resignation is effective March 22.

In an interview Thursday, Cooper, 56, said he is leaving Trimedyne “mostly because I feel the company is in a better position now to achieve its long-term goals and there are other things I want to do.” He said he was evaluating several employment prospects.

Wall Street reacted negatively to the news. Trimedyne’s stock dropped 87.5 cents to $4.625 on volume of 195,300 shares.

David Duclos, medical technology analyst for Wessels, Arnold & Henderson, based in Minneapolis, said Cooper’s resignation was a surprise.

“I thought the company was making very good progress under his leadership,” Duclos said. He credited Cooper for deciding that Trimedyne should diversify its technology after sales of its thermal laser catheter took a steep dive.

While Trimedyne’s thermal catheter originally was hailed as a technological breakthrough and worked for opening blocked arteries of the leg, it failed to win federal approval for use in the heart, which is a potentially more lucrative market.

And much of the medical community began to prefer the “cold laser” that breaks through plaque and is believed to cause less damage to surrounding tissue than the thermal laser. Cooper also instigated major belt-tightening measures at Trimedyne, selling off the company’s non-medical subsidiary in Florida last year and cutting the staff from about 200 workers in 1988 to 70. This year the firm moved from Tustin to smaller quarters in Irvine.