DE4139865C2 - Tunable two-wavelength laser for super heterodyne interferometers - Google Patents

Description

The invention relates to a tunable two-wavelength laser according to the preamble of claim 1.

Such a laser is known from EP 0 443 902 A2. To build absolute measuring super heterodyne interferometers Laser light sources required, which on the one hand have the lowest possible Line width, on the other hand, two different laser waves generate lengths, which differ in frequency by about 0-30 GHz other can be detuned, so that when they are superimposed a synthe table wavelength arises, the wavelength between 1 cm and almost can be tuned infinitely.

From US 4,504,950 it is known to close an air gap for frequency tuning use which is at an angle to the optical axis and in its extent can be varied.

DD 123 498 is a laser mirror for Mode reflection is known, which consists of two broad-shaped transparent to the laser radiation Bodies exist that enclose a gap that at the Brewster angle to Laser radiation is available and its extent can be varied.

The object of the present invention is a system of a solid body to show lasers of the type mentioned, which, constructed as semiconductor laser-pumped solid-state laser, on the one hand extremely compact thirdly, has a narrow line width essential properties is two polarized perpendicular to each other To generate beams which have a frequency around the entire range of 0-30 GHz can be detuned against each other.

This object is achieved by the measures indicated in claim 1. Further details of the invention emerge from the subclaims and the description in which an embodiment with reference to the drawing is described.

The system presented here is based on the single-frequency lasers the short absorption length, as z. B. by Kintz and Baer in "IEEE J. QE, Vol. 26, No. 9, Sept. 1990, pp 1457-1459 ". The laser material (eg Nd: YVO₄)  or the doping and the pump line are chosen so that the formation of only one longi tudinal fashion is guaranteed. However it must be taken into account that the absorption length is sufficiently long, to allow a detuning around 30 GHz without fashion jumps. The minor Laser line width is due to a quasi-monolithic structure high mecha stability achieved.  

The construction of such a laser, which two perpendicular to each other Polarized rays emitted is shown in drawing 1. A suitable Neter laser crystal of originally cuboid shape is under an angle α with respect to the optical axis [α = (90 ° -Brewster angle)] cut.

The area 1 is formed as a coupling mirror of a conventional laser (highly transmissive for the pump wavelength and highly reflective for the laser wavelength) and forms the mirror which is common to both partial beams. At the first cut surface 2 , part of the radiation is polarized 100% parallel to the plane of incidence and deflected to the surface 3 due to the Brewster angle, which, like the surface 4 , is partially reflective for the laser radiation.

This partial beam forms the portion of the laser radiation which is in its frequency is fixed and thus serve as an absolute frequency standard can. A tuning of this frequency can, for example, by heating tion of the crystal piece can be achieved.

The remaining portion of the laser radiation passes through the cut surfaces 2 and is reflected on the surface 4 , with radiation generated in the second prism perpendicular to this being reflected on the second cut surface towards the air gap in the direction of the surface 5 . However, a fashion cannot develop between surface 5 and surface 4 , since surface 5 has no mirror coating. By varying the air gap, which is delimited by the cut surfaces 2 , the resonator length for the partial beam passing through both prisms can be varied and thus its frequency can also be changed.

Thus, two partial beams polarized perpendicular to each other are available that detune each other and to an absolute frequency can be coordinated.  

The variation of the air gap can on the one hand by piezoelectric Actuators take place, on the other hand polymer films, as described in DE 40 39 455 A1, or flexible adhesives can be used. The latter are characterized by high adhesive strength, high flexibility high thermal expansion and electrical conductivity, so that an ohmic heater uses the adhesive layer for tuning can be.

Such a structure is characterized by high mechanical stability from what brings small line widths with it.

Claims (5)

1. Tunable two-wavelength laser, in which a vibration mode is split into two mutually perpendicularly polarized partial modes and the frequency of one partial mode can be detuned relative to the frequency of the other partial mode, characterized in that

• the laser-active medium is a single-frequency laser crystal that is pumped with a semiconductor laser,
• the laser crystal consists of two parts which include an air gap which runs at the complement angle of the Brewster angle of the laser-active medium with respect to the optical axis of the laser resonator,
• - The width of the air gap can be changed, whereby the frequency of a partial mode can be detuned.

2. Laser according to claim 1, characterized in that the frequency at other partial mode serves as a reference frequency, which is by means of temperature changes can be coordinated. 3. Laser according to claim 1 or 2, characterized in that the Length change of the air gap by means of an adhesive of high thermal Expansion and good electrical conductivity through ohmic heating is achieved, the adhesive simultaneously connecting the serves both crystals. 4. Laser according to claim 1 or 2, characterized in that the Change in length of the air gap by means of a piezoelectric polymer foil is effected. 5. Laser according to claim 1 or 2, characterized in that the The length of the air gap is changed using a piezoceramic.