Single crystal diamond elements having convex surfaces and methods of its fabrication

93:

• The method of claim 92, wherein the laser beam is applied to the blank in a direction perpendicular to the first axis, and the translation of the blank relative to the laser beam is in a plane perpendicular to the laser beam.

94:

• The method of claim 92, wherein the translation of the laser beam relative to the blank is achieved by translating the blank and keeping the laser stationary.

95:

• The method of claim 92, wherein the rotationally symmetrical surface is a spherical surface, the translation of the laser beam relative to the blank following a path substantially described by an arc of a circle having a central axis passing through the centre of curvature of the spherical surface;
• whereby the simultaneous rotation of the blank and translation of the laser beam relative to the blank results in the substantially spherical surface being cut in the blank.

96:

• The method of claim 95, wherein the path followed by the laser beam relative to the blank deviates in a predetermined manner from the arc of the circle when the laser beam is close to the axis of rotation of the blank.

97:

• The method of claim 92, wherein the blank is mounted on a rod rotatable about the first axis.

98:

• The method of claim 97, wherein the blank is brazed onto the rod.

99:

• The method of claim 98, wherein the diamond element remains attached to the rod in final use.

100:

• A method of polishing a spherical surface on a single crystal diamond element, comprising:
• rotating the element about a first axis at a first rate of rotation;
• pressing a cup having a polishing surface against the spherical surface, the polishing cup rotating about a second axis at a second rate of rotation much higher than the first rate.

101:

• The method of claim 100, wherein the cup additionally rotates about a third axis at a third rate lower than the first rate, the third axis being perpendicular to the first axis and passing through the first axis at the centre of curvature of the spherical surface, the rotation about the third axis being an oscillatory motion describing less than a full circle.

102:

• The method of claim 101, wherein the rate of rotation about the third axis is variable.

103:

• The method of claim 102, wherein the rate of rotation about the third axis is randomly variable.

104:

• The method of claim 100, wherein the first axis is aligned along the crystallographic <100> direction.

105:

• The method of claim 100, wherein the first axis is aligned along the crystallographic <111> direction.

106:

• The method of claim 100, wherein the polishing surface comprises a layer of diamond powder embedded in a former.

107:

• The method of claim 106, wherein the former is resin.

108:

• The method of claim 100, wherein the polishing surface is concave and substantially matches the shape of the spherical surface.

109:

• The method of claim 100, wherein the polishing surface is initially substantially flat, the polishing surface being worn by being pressed against the spherical surface into a complementary concave spherical shape.

110:

• The method of claim 100, wherein the spherical surface is first formed.

111:

• A single crystal diamond element having a spherical surface formed or polished using the method of claim 92.

112:

• An element of single crystal diamond material having a convex surface formed thereon, the convex surface having a root mean square roughness of less than about 30 nm, the element further having at least one of the properties from the following list:
• the convex surface including a spherical segment for which the maximum peak to valley deviation from a perfect spherical surface is less than about 5 μm;
• the convex surface including a spherical segment for which the RMS deviation of the spherical segment, as measured by averaging over the square of deviations over the spherical segment, is less than or equal to about 500 nm.

113:

• The element of claim 112, wherein the convex surface further has at least one of the properties from the following list:
• a radius of curvature less than about 20 mm;
• the convex surface including a spherical segment having a conical half-angle greater than about 10°.

114:

• The element of claim 112, wherein the element is formed substantially in the shape of a sphere.

115:

• The element of claim 112, further comprising a flat surface on a side of the element opposite to the convex surface.

116:

• The element of claim 115, wherein the flat surface has a surface roughness at least as low as the convex surface.

117:

• The element of claim 115, further comprising a tapered section between the convex surface and the flat surface.

118:

• The element of claim 117, wherein the tapered section comprises a plurality of polished facets.

119:

• The element of claim 115;
• wherein the element has a thickness in a direction substantially normal to the flat surface correct to within at least 2 μm of an ideal thickness.

120:

• The element of claim 119, wherein the element has a generally hemispherical shape with an ideal thickness equal to the radius of curvature of the hemisphere.

121:

• The element of claim 119, wherein the element has a generally super-hemispherical shape and an ideal thickness given by t=r(1+1/n), where t is the thickness of the element in a direction substantially normal to the flat surface, r is the radius of curvature of the super-hemisphere, and n is the refractive index of the diamond material from which the element is formed.

122:

• The element of claim 112, wherein the single crystal diamond material is natural diamond.

123:

• The element of claim 112, wherein the single crystal diamond material is synthetic diamond.

124:

• The element of claim 123, wherein the synthetic diamond material is formed by High Pressure and High Temperature synthesis.

125:

• The element of claim 123, wherein the single crystal diamond material is CVD diamond.

126:

• A single crystal diamond lens comprising a diamond element as claimed in claim 112.

127:

• A single crystal diamond solid immersion lens comprising a diamond element as claimed in claim 112.

130:

• A tool tip for use in a metrology apparatus comprising a diamond element as claimed in claim 112.

131:

• A reference sphere for use in measuring hole diameters comprising a single crystal diamond element as claimed in claim 111.

132:

• A reference sphere for use in calibrating measurement instruments comprising a single crystal diamond element as claimed in claim 111.

133:

• A reference sphere for use as a reference spacer or as a spacer for defining a surface comprising a single crystal diamond element as claimed in claim 111.