WO2014200560A1 - High power air-cooled sampling device - Google Patents

Abstract

A laser beam sampling device including: a dual prismatic element, each element having at least one partially reflective surface, disposed in one housing with a rotation of about 90 degree between optical prismatic elements; an input aperture for the laser beam partially reflected by first prismatic element from its front surface towards a second prismatic element and reflected by its front surface to an output aperture. The prismatic elements are mounted on an optical bench and their first partially reflecting surfaces are rotated by 90 degrees. A special air connector with compressed air actively cleans and cools the partially reflecting surfaces. Most of laser power exits to prevent heat load to sampling elements.

Description

HIGH POWER AIR-COOLED SAMPLING DEVICE

Field of the invention

The invention relates to the field of high power air cooled sampling device, specifically to a method of beam attenuation by beam sampling with minimal distortion.

Background of the invention

Laser beam analysis frequently requires the beam to be attenuated by many orders of magnitude before reaching a measuring instrument input aperture. This is specifically true with high power lasers reaching the kilowatts power range. Beam attenuator frequently overheats and a non distorting cooling device is required. A novel beam attenuator with built in air cooling, non distorting optics and adjusting mechanics is disclosed.

The device comprises of an input aperture, two roof type prismatic elements rotated by 90 degrees to each other and a mechanical housing capable of rotating along the center of output aperture.

Attenuation is achieved by 90 degree reflection from each front surface of at least two prismatic elements orthogonally rotated to each other and actively cooled by

compressed gas.

The invention relates to the field of attenuation of high power lasers used for material processing.

Description of the Related Art

In known laser beam profilers, measurement is performed by exposing a detection area to an incoming input laser beam. Laser power level is adjusted by a set of optical filters disposed in the laser pathway to prevent damage to the detector. Various alternative methods are used for attenuating the intensity of light beams, for example beam sampling by a partially reflecting surface is used to greatly reduce the beam power reaching the detection surface.

Prior art systems based on beam sampling is effective for relative low power applications since they lack an intrinsic cooling device. Usually distortion of beams polarization will occur when reflective beam sampling is involved due to a well known effect governed by Brewster reflection angles. This effect causes the reflected beam to be differently polarized as a function of beams reflection angle In yet similar application beam sampling is performed by solid elements were the beam passes through a solid optical element and sampled, when the beam exits, sampling is achieved at the interface between the solid material and surrounding air. A typical system for beam attenuation by sampling using a solid optical element is described in US Patent Publication No. 2003/0223132A1. Attenuating a beam through such an optical arrangement will distort the original beam especially if it is converging or diverging and thus it is unpractical for direct highly accurate measuring method.

Moreover when high power laser are involved, unless effectively cooled, optical surfaces will distort and change reflected beam characteristics.

A specialized cooling technique that capitalizes on compressed air expanding through a nozzle is disclosed. This cooling enhancement technology is especially applicable in systems intended to examine high power lasers. The cooling increases performance by two mechanisms; compressed air cooling by expansion through an air nozzle and air flow on beam sampler creating a uniform temperature by heat convection on reflecting surface.

Secondly high power laser beams will frequently burn dust particles flowing in air, which later will be deposited on sampling surface will accelerating surface quality destruction. The cooling technique will also provide clean air which will blow away dust particles

Summary of the Invention

One feature of uniqueness of the present sampling device is that this device achieves and sometimes overcomes the performance of the systems existing in the market for measuring high power lasers without distortion. The apparatus is based on two prismatic elements rotated by 90 degree to each other having an actively cooled input aperture and output aperture where the beam power is greatly reduced. Most of laser power is redirected to pass through the sampling device at a different direction away from sampling device. The beam sample device will accept lasers of different power levels and the beam emerging from output aperture has same distribution as the original beam that incidents input aperture but with reduced power.

Due to the above features, the proposed beam sampling device is potentially usable for a large variety of high power lasers.

Another advantage of the proposed aesthetic treatment device is that it can be built of prismatic elements of different materials where the material best mach the lasers wavelength. Common materials are glass, fused silica, germanium, ZnS, ZnSe and others.

Many disadvantages of prior art optical attenuation and sampling devices are

advantageously solved by aspects of the present invention. A partial list is as follows:

In prior art systems a high power light or laser has to be attenuated by sampling or by optical filters before analysis. In case of focused beams, usually the attenuated beam is distorted. It is an aspect of the present invention to overcome this drawback by sampling a focused laser beam or light without any distortion.

Some prior art samplings are performed without polarization preservation. It is another aspect of the present invention to perform beam sampling while preserving the original laser polarization.

In some prior art devices, the irradiated area is not actively cleaned from burned dust particles, causing potentially catastrophic damage at input aperture area, it is yet another aspect of the present invention art to provide active cleaning by compressed clean air.

In prior art devices, there is no active air cooling to the sampling surface.

It is another aspect of the present invention to provide active cooling preventing thermal distortion.

According to an aspect of the present invention, a miniature beam sampling device for high laser power applications attenuates the incoming beam by partial reflection from first surface of an optical material. Sampled beam is further redirected to a second optical surface which is rotated by 90 degrees. Second surface since rotated will sample the incoming beam and correct its polarization distortion coursed by first reflection. The amount of partial reflection from each surface is a function of optical material used for example this material could be glass, sapphire, ZnS, ZnSe, Germanium or other commonly used optical materials.

The two prismatic elements are preferable made of glass and having a partial reflection of about 3% to 4%. Since it is used in an arrangement of minimum two consecutive reflections the expected attenuation of sampled beam for this case would be about 0.001 from original beam.

There is provided in accordance with an embodiment of the present invention, a laser beam sampling device comprising: dual optical prismatic element, rotated at 90 degree to each other, an input aperture for laser power partially reflected by first prismatic element, toward the second prismatic element partially reflected towards an output, a cooling orifice connected to external compressed air cooling and cleaning the device, an opening for main beam to pass through without heating the device, a rotating Mechanism centered to output aperture allowing rotational adjustment along the output axis causing the output aperture is rotated along its optical According to an embodiment the prismatic elements are from different optical materials or have various surface coating according to application

Brief Description of the Drawings

FIG. 1 is a 3D schematic representation of an actively cooled beam sampling device

FIG. 2 is a side view of the cooled beam sampler as disclosed in fig. 1

FIG. 3 is a front view of the actively cooled sampler as shown in FIG. 1 ;

FIG. 4 is a view of the device shown in FIG. 1 along with mechanical enclosure.

Fig 5 is a 3D view showing the rotation axis of beam sampling

These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

Detailed Description of Embodiments Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.

Aspects of the present invention disclose a beam sampling device enabling sampling of focused and non-focused light beams to be examined directly on an analyzing detector for power measurement and beam profiling.

Aspects of the present invention disclose a cooled beam sampling with built in optical attenuator.

Aspects of the present invention disclose a beam sampling device were the beam is sampled by partial reflection of two prismatic elements rotated by 90 degrees to each other. The rotation will cancel any distortion in original beam polarization caused by the partial reflection of first prism.

FIG. 1 is a 3D schematic representation of a beam sampling device. A prismatic element 1 having a partially reflective surface 2 is disclosed. Other prismatic element 3 is rotated by 90 degrees around the reflected beam from first prismatic element. An incoming beam 4 is partially reflected by first prismatic element. This reflection is denoted as 5 while main beam 6 passes through the prismatic elements, its direction is according to laws of refraction when passing through a glass element. Prismatic element 3 has a front surface (not shown) which samples the beam again denoted as 7. The detection area 8 receives the beam after dual sampling from first and second prismatic elements.

Detection area 8 could be laser powers meter, a beam profiler or some other generic detection system. The miniature device 9 is an air nozzle supplied with compressed air, preferably, but not necessarily air, which actively cools the surface 2 to prevent excessive heating and distortion. This cooling is also an active cleaning device preventing torched particles to deposit on prismatic elements. The cooling device may be connected to a compressed air supply by a miniature hose denoted as 10. An additional beam damping is provided and in this case is a metal piece 11 and is a part of housing. Beam 12 will be damped at 11 and transformed to heat.

In FIG. 2 a side view of FIG 1 is disclosed clearly showing the incoming main beam 4 its reflected part 5 and transmitted main part beam 6. Fig 3 is a front view clearly displaying sampled beam 5 from first prismatic element and sampled beam 7 from second prismatic element. Sampled beam 7 is partially reflected by surface 13 towards detection area 8. Sampling is provided by natural reflection from front surfaces of prismatic elements. For glass these front surfaces will reflect 3 to 4 percent each. Coating front surfaces with antireflection coating can reduce reflection and thus sampling ratio as low as .1 percent per surface is achievable

Fig 4 shows the sampling prismatic elements with its mechanical housing 14, its sensing detector 8 and the mechanical rim 15 which permits relative angular rotation of sampling device. Angular rotation is relative to housing. Prismatic elements are bonded to housing at points 16.

Fig 5 is a 3D view of sampling element and its rotation direction.

Known methods use an optical filter or beam sampler that will distorted the beam due the lack of effective front surface cleaning and cooling. For example, an absorptive or reflecting filter can withstand low power densities especially absorptive filters, while reflective filters will back reflect with possible damage to the incoming beam. Moreover lack of active cleaning and cooling will limit filter life span and distort the beam.

One of the main limitations of existing methods is the difficult way to adjust the direction of input aperture to the direction of incoming beam, which is solved on our beam sampler by the capability of rotating the beam sampler along its output axis.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims

What is claimed is:

A laser beam sampling device comprising:

Dual optical prismatic elements rotated by 90 degree to each other

An input aperture for laser to be partially reflected by first prismatic

Element towards the second prismatic element partially reflected to an

Output

A cooling orifice connected to external compressed air

The laser beam sampling device according to claim 1 wherein the output aperture is rotated along its optical axis

The laser beam sampling device according to claim 1 wherein the Prismatic elements are from different optical material or have various Optical coating according to application