The term "laser harp" and the first working laser harp were invented and made by Bernard Szajner in 1980.. It has subsequently been used in a number of different designs, including a MIDI version invented by Philippe Guerre, and a recent one created by Yan Terrien They have also been used in public art installations such as those created by Jen Lewin on display at Lincoln Center in 2000 and Burning Man 2005.
In this design, only a binary (on / off) trigger is created by the breaking of the beam, which is sufficient to trigger any number of events (musical or otherwise) as determined by the data analyzer / software in question. In order to generate more control data, such as a continuous range of values like those found in many MIDI controllers, several approaches are available: 1) using an infrared or ultrasonic rangefinder attached to the instrument, such that the position of the hand "plucking the string" is determined; 2) using a laser-based rangefinder to determine the distance from the hand to the laser's starting or ending point (and possibly using this laser itself as the string); and 3) using a camera to track the position and motion of the laser dot on the hand, or the length of the exposed beam if visible, then calculating a continuous value based upon a reference. Other possibilities no doubt exist. Each of these possibilities poses particular challenges and costs, though the first one is relatively inexpensive and straightforward to implement, and can use the same microcontroller which drives the lasers and reads the detectors.
The laser harp may be framed or frameless, the framed type using an array of photodiodes or photoresistors inside the upper part of the frame to detect blocking of the laser beams. The frameless design is somewhat more elaborate, relying on the light being reflected back to a single photodiode. The fan of laser beams is actually a single beam being scanned into a fan pattern. By matching the timing of the reflected beam, it can be determined which of the beams is being blocked and which note needs to be heard. Alternative designs make use of multiple lasers; in these designs, each laser can be independently controlled (pulsed on and off) to simulate playback of prerecorded notes.
The laser harp was not used on his Aero concert but it was revived in 2004 and has been used since then, mostly on his tracks Second Rendez-Vous and Chronologie Part 3.
Although the laser harp makes no actual sound itself, (merely triggering a note on a synthesizer) Jarre has consistently used it to trigger a particular sound which has become synonymous with his use of the laser harp, which is based on a preset from the Elka Synthex synthesizer.
Many people suspect the laser harp, as well as some other custom instruments, is a fake; careful inspection of concert footage of Jarre playing the harp occasionally indicates that striking the same beam produces different notes, suggesting that the harp is simply designed to trigger the next correct note irrespective of which beam is broken. However, this method is unreliable, as videos are invariably edited before release. As an example, in the live recording of the Paris La Défense concert as broadcast on the Europe 2 radio station, it can be clearly heard that the laser harp is malfunctioning, and in fact after a while gets replaced by a different synthesizer. In the video release, no trace is left of this malfunction. Also the harp is fitted with foot pedals for selecting scales, making it quite eligible that the same beam can house different notes.
Others believe that the laser harp has been proven to work and has been played by Jarre live occasionally, especially on his 1997 concert tour and Oxygen in Moscow. Other notable live playings of the harp occurred during Chronologie 3 at Beijing as well as at Hymn to the Akropolis and during Calypso 2 at Paris La Defense. In the European Tour 1997 Jarre played Laser Harp for the first song on that concert, the famous first notes of Oxygene VII, played three times without any other instrument or sound. Also, there was a laser harp on display at the 1989 Concert d'Images exhibition in Paris, which could be played by the public.
However, the harp at the Manchester venue of the Europe in Concert tour was certainly fake, as the laser failed during the performance but the lead line, actually played on stage by Francis Rimbert, continued.
Recently, Steve Hobley was able to reproduce a working model of Jarre's harp using a 250mw green laser, scanner and some inexpensive components (including a Wii Remote). Plans and source code can be found here